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Is 456 2000 Is 456 2000 Document Transcript

  • IS 456 : 2000 Indian Standard PLAIN AND REINFORCED CONCRETE - CODE OF PRACTICE ( Fourth Revision ) ICS 91.100.30 0 BIS 2000 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002July 2000 Price Rs 260.00
  • IS456: 2000 Indian Standard PLAINAND REINFORCEDCONCRETE- CODEOFPRACTICE ( Fourth Revision )FOREWORDThis Indian Standard (Fourth Revision) was adopted by the Bureau of Indian Standards, after the draft finalixedby the Cement and Concrete Sectional Committee had been approved by the Civil Engineering Division Council.This standard was first published in 1953 under the title ‘Code of practice for plain and reinforced concrete forgeneral building construction’ and subsequently revised in 1957. The code was further revised in 1964 andpublished under modified title ‘Code of practice for plain and reinforced concrete’, thus enlarging the scope ofuse of this code to structures other than general building construction also. The third revision was published in1978, and it included limit state approach to design. This is the fourth revision of the standard. This revisionwas taken up with a view to keeping abreast with the rapid development in the field of concrete technology andto bring in further modifications/improvements in the light of experience gained while using the earlier versionof the standard.This revision incorporates a number of important changes. The major thrust in the revision is on the followinglines: a) In recent years, durability of concrete structures have become the cause of concern to all concrete technologists. This has led to the need to codify the durability requirements world over. In this revision of the code, in order to introduce in-built protection from factors affecting a structure, earlier clause on durability has been elaborated and a detailed clause covering different aspects of design of durable structure has been incorporated. b) Sampling and acceptance criteria for concrete have been revised. With tbis revision acceptance criteria has been simplified in line with the provisions given in BS 5328 (Part 4):1990 ‘Concrete: Part 4 Specification for the procedures to be used in sampling, testing and assessing compliance of concrete’.Some of the significant changes incorporated in Section 2 are as follows: a) All the three grades of ordinary Portland cement, namely 33 grade, 43 grade and 53 grade and sulphate resisting Portland cement have been included in the list of types of cement used (in addition to other types of cement). b) The permissible limits for solids in water have been modified keeping in view the durability requirements. cl The clause on admixtures has been modified in view of the availability of new types of admixtures including superplasticixers. d) In Table 2 ‘Grades of Concrete’, grades higher than M 40 have been included. e) It has been recommended that minimum grade of concrete shall be not less than M 20 in reinforced concrete work (see also 6.1.3). 0 The formula for estimation of modulus of elasticity of concrete has been revised. 8) In the absenceof proper correlation between compacting factor, vee-bee time and slump, workability has now been specified only in terms of slump in line with the provisions in BS 5328 (Parts 1 to 4). h) Durability clause has been enlarged to include detailed guidance concerning the factors affecting durability. The table on ‘Environmental Exposure Conditions’ has been modified to include ‘very severe’ and ‘extreme’ exposure conditions. This clause also covers requirements for shape and size of member, depth of concrete cover, concrete quality, requirement against exposure to aggressive chemical and sulphate attack, minimum cement requirement and maximum water cement ratio, limits of chloride content, alkali silica reaction, and importance of compaction, finishing and curing. j) A clause on ‘Quality Assurance Measures’ has been incorporated to give due emphasis to good practices of concreting. k) Proper limits have been introduced on the accuracy of measuring equipments to ensure accurate batching of concrete. 1
  • IS 456 : 2000 m) The clause on ‘Construction Joints’ has been modified. n) The clause on ‘Inspection’ has been modified to give more emphasis on quality assurance.The significant changes incorporated in Section 3 are as follows: a) Requirements for ‘Fire Resistance’ have been further detailed. b) The figure for estimation of modification factor for tension reinforcement used in calculation of basic values of span to effective depth to control the deflection of flexural member has been modified. cl Recommendations regarding effective length of cantilever have been added. 4 Recommendations regarding deflection due to lateral loads have been added. e) Recommendations for adjustments of support moments in restrained slabs have been included. 0 In the detemination of effective length of compression members, stability index has been introduced to determine sway or no sway conditions. g) Recommendations have been made for lap length of hooks for bars in direct tension and flexural tension. h) Recommendations regarding strength of welds have been modified. j) Recommendations regarding cover to reinforcement have been modified. Cover has been specified based~on durability requirements for different exposure conditions. The term ‘nominal cover’ has been introduced. The cover has now been specified based on durability requirement as well as for fite requirements.The significant change incorporated in Section 4 is the modification-of the clause on Walls. The modified clauseincludes design of walls against horizontal shear.In Section 5 on limit state method a new clause has been added for calculation of enhanced shear strength ofsections close to supports. Some modifications have also been made in the clause on Torsion. Formula forcalculation of crack width has been-added (separately given in Annex P).Working stress method has now been given in Annex B so as to give greater emphasis to limit state design. Inthis Annex, modifications regarding torsion and enhanced shear strength on the same lines as in Section 5 havebeen made.Whilst the common methods of design and construction have been covered in this code, special systems ofdesign and construction of any plain or reinforced concrete structure not covered by this code may be permittedon production of satisfactory evidence regarding their adequacy and safety by analysis or test or both(see 19).In this code it has been assumed that the design of plain and reinforced cement concrete work is entrusted to aqualified engineer and that the execution of cement concrete work is carried out under the direction of a qualifiedand experienced supervisor.In the formulation of this standard, assistance has been derived from the following publications: BS 5328-z Part 1 : 1991 Concrete : Part 1 Guide to specifying concrete, British Standards Institution BS 5328 : Part 2 : 1991 Concrete : Part 2 Methods for specifying concrete mixes, British Standards Institution BS 5328 : Part 3 : 1990 Concrete : Part 3 Specification for the procedures to be used in producing and transporting concrete, British Standards Institution BS 5328 : Part 4 : 1990 Concrete : Part 4 Specification for the procedures to be used in sampling, testing and assessing compliance of concrete, British Standards Institution BS 8110 : Part 1 : 1985 Structural use of concrete : Part 1 Code of practice for design and construction, British Standards Institution BS 8110 : Part 2 : 1985 Structural use of concrete : Part 2 Code of practice for special circumstances, British Standards Institution AC1 3 19 : 1989 Building code requirements for reinforced concrete, American Concrete Institute AS 3600 : 1988 Concrete structures, Standards Association of Australia 2
  • IS 456 : 2000 DIN 1045 July 1988 Structural use of concrete, design and construction, Deutsches Institut fur Normung E.V. CEB-FIP Model code 1990, Comite Euro - International Du BelonThe composition of the technical committee responsible for the formulation of this standard is given inAnnex H.For the purpose of deciding whether a particular requirement of this standard is complied with, the final value,observed or calculated, expressing the result of a test or analysis shall be rounded off in accordance withIS 2 : 1960 ‘Rules for rounding off numerical values (revised)‘. The number of significant places retained in therounded off value should be the same as that of~the specified value in this standard.
  • As in the Original Standard, this Page is Intentionally Left Blank
  • IS456:2000 CONTENTS PAGE SECTION 1 GENERAL 111 SCOPE 112 REFERENCES 113 TERMINOLOGY 114 SYMBOLS SECTION 2 -MATERIALS, WORKMANSHIP, INSPECTION AND TESTING 135 MATERIALS 13 5.1 Cement -13 5.2 Mineral Admixtures 14 5.3 Aggregates 14 5.4 Water 15 55 Admixtures 15 5.6 Reinforcement 15 5.7 Storage of Materials 156 CONCRETE 15 6.1 Grades 15 6.2 Properties of Concrete 17 7 WORKABILITY CONCRETE OF 17 8 DURABILITY CONCRETE OF 17 8.1 General 18 8.2 Requirements for Durability 22 9 CONCRETE Mrx PROPORTIONING 22 9.1 Mix Proportion 22 9.2 Design Mix Concrete 23 9.3 Nominal Mix Concrete 23 10 PRODUCTION CONCRETE OF 23 10.1 Quality Assurance Measures 24 10.2 Batching 24 10.3 Mixing 25 11 FORMWORK 25 11.1 General 25 11.2 Cleaning and Treatment of Formwork 25 1I .3 Stripping Time 25 12 ASSEMBLY REINFORCEMENT OF 26 13 TRANSPORTING, PLACING, COMPACTION CURING AND 26 13.1 Transporting and Handling 26 13.2 Placing 26 13.3 Compaction
  • IS 456 : 2000 PAGE 13.4 Construction Joints and Cold Joints 27 13.5 Curing 27 13.6 Supervision 2714 CONCRERNG UNDER SPECIAL CONDITIONS 27 14.1 Work in Extreme Weather Conditions 27 14.2 Under-Water Concreting 27 15 SAMPLING STRENGTH DESIGNED AND OF CONCRETE Mrx 29 15.1 General 29 15.2 Frequency of Sampling 29 15.3 Test Specimen 29 15.4 Test Results of Sample 29 16 ACCEPTANCE CRITERIA 29 17 INSPECI-ION TEFXJNG STRWTURE AND OF 30 SECTION 3 GENERAL DESIGN CONSIDERATION 18 BASESFORDEIGN 32 18.1 Aim of Design 32 18.2 Methods of Design 32 18.3 Durability, Workmanship and Materials 32 18.4 Design Process 32 I 9 LOADS FORCES AND 32 19.1’ General 32 19.2 Dead Loads 32 19.3 Imposed Loads, Wind Loads and Snow Loads 32 19;4 Earthquake Forces 32 19.5 Shrinkage, Creep and Temperature Effects 32 19.6 Other Forces and Effects 33 19.7 Combination of Loads 33 19.8 Dead Load Counteracting Other Loads and Forces 33 19.9 Design Load 33 20 STABILITY THESTRUCTURE OF 33 20.1 Overturning 33 20.2 Sliding 33 20.3 Probable Variation in Dead Load 33 20.4 Moment Connection 33 20.5 Lateral Sway 33 2 1 FIRERESISTANCE 33 22 ANALYSIS 34 22.1 General 34 - 22.2 Effective Span 34 22.3 Stiffness 35 6
  • IS456:2000 PAGE 22.4 Structural Frames 35 22.5 Moment and Shear Coefficients for Continuous Beams 35 22.6 Critical Sections for Moment and Shear 36 22.7 Redistribution of Moments 36 .23 BEAMS 36 23.0 Effective Depth 36 23.1 T-Beams and L-Beams 36 23.2 Control of Deflection 37 23.3 Slenderness Limits for Beams to Ensure Lateral Stability 3924 SOLIDSLABS 39 24.1 General 39 24.2 Slabs Continuous Over Supports 39 24.3 Slabs Monolithic with Supports 39 24.4 Slabs Spanning in Two Directions~at Right Angles 41 24.5 Loads on Supporting Beams 4125 COMPRESSION MEZMBERS 41 25.1 Definitions 41 25.2 Effective Length of Compression Members 42 25.3 Slenderness Limits for Columns 42 25.4 Minimum Eccentricity 4226 REQUIREMENTS GOVERNING AND REINFORCEMENT DETAILING 42 26.1 General 42 26.2 Development of Stress in Reinforcement 42 26.3 Spacing of Reinforcement 45 26.4 Nominal Cover to Reinforcement 46 26.5 Requirements of Reinforcement for Structural Members 46 27 EXPANSION JOMTS 50 SECTION 4 SPECIAL DESIGN REQUIREMENTS FOR STRUCTURAL MEMBERS AND SYSTEMS 28 CONCRETE CORBELS 51 28.1 General 51 28.2 Design 51 29 DEEP BEAMS 51 29.1 General 51 29.2 Lever Arm 51 29.3 Reinforcement 51 30 RIBBED, HOLLOWBLOCKORVOIDEDSLAB 52 30.1 General 52 30.2 Analysis of Structure 52 30.3 Shear 52 30.4 Deflection 52
  • IS 456 : 2000 PAGE 30.5 Size and Position of Ribs 52 30.6 Hollow Blocks and Formers 52 30.7 Arrangement of Reinforcement 53 30.8 Precast Joists and Hollow Filler Blocks 5331 FLAT SLABS 53 3 1.1 General 53 3 1.2 Proportioning 53 3 1.3 Determination of Bending Moment 53 3 1.4 Direct Design Method 54 3 1.5 Equivalent Frame Method 56 3 1.6 Shear in Flat Slab 57 3 1.7 Slab Reinforcement 59 3 1.8 Openings in Flat Slabs 6132 WALLS 61 32.1 General 61 32.2 Empirical Design Method for Walls Subjected to Inplane Vertical Loads 61 32.3 Walls Subjected to Combined Horizontal and Vertical Forces 62 32.4 Design for Horizontal Shear 62 32.5 Minimum Requirements for Reinforcement in Walls 62 33 STAIRS 63 33.1 Effective Span of Stairs 63 33.2 Distribution of Loading on Stairs 63 33.3 Depth of Section 63 34 Foort~~s 63 34.1 General 63 34.2 Moments and Forces 64 34.3 Tensile Reinforcement 65 34.4 Transfer of Load at the Base of Column 65 34.5 Nominal Reinforcement 66 SECTION 5 STRUCTURAL DESIGN (LIMIT STATE METHOD) 35 SAFETY AND SERVKEABlLITY kKNIREMl?N’l’s 67 35.1 General 67 35.2 Limit State of Collapse 67 35.3 Limit States of Serviceability 67 35.4 Other Limit States 67 36 CHARACTERISTIC AND DESIGN VALUES PARTUL AND FACTORS SAFEI”Y 67 36.1 Characteristic Strength of Materials 67 36.2 Characteristic Loads 67 36.3 Design Values 68 36.4 Partial Safety Factors 68 37 ANALYSIS -68 37.1 Analysis of Structure 68 8
  • PAGE38 LIMITSTATE COLLAPSE :FLEXURE OF 69 38.1 Assumptions 6939 LIMITSTATE COLLAPSE: OF COMPRESSION 70 39.1 Assumptions 70 39.2 Minimum Eccentricity 71 39.3 Short Axially Loaded Members in Compression 71 39.4 Compression Members with Helical Reinforcement 71 39.5 Members Subjected to Combined Axial Load and Uniaxial Bending 71 39.6 Members Subjected to Combined Axial Load and Biaxial Bending 71 39.7 Slender Compression Members 7140 LLWTSTATE OF-COLLAPSE : SW 72 40.1 Nominal Shear Stress 72 40.2 Design Shear Strength of Concrete 72 40.3 Minimum Shear Reinforcement 72 40.4 Design of Shear Reinforcement 72 40.5 Enhanced Shear Strength of Sections Close to Supports 7441 LJMITSTATE COLLAPSE OF : TORSION 74 41.1 General 74 4 1.2 Critical Section 75 4 1.3 Shear and Torsion 75 4 1.4 Reinforcement in Members Subjected to Torsion 7542 LIMITSTATKOF SERVICEABILITY: DEKIZC~ION 75 42.1 Flexural Members 7543 LIMITSTATE SERVICEABILITY: OF CRACKING 76 43.1 Flexural Members 76 43.2 Compression Members 76 4NNEXA LIST OF REFERRED INDIAN STANDARDS 77 ANNEXB STRUCTURAL DESIGN (WORKING STRESS METHOD) 80 B-l GENERAL 80 B-l.1 General Design Requirements 80 B- 1.2 Redistribution of Moments 80 B-l.3 Assumptions for Design of Members 80 B-2 PEaMIsstBLE STrtEssEs 80 B-2.1 Permissible Stresses in Concrete 80 B-2.2 Permissible Stresses in Steel Reinforcement 80 B-2.3 Increase in Permissible Stresses 80 B-3 I’iuu@ssm~~ Lam INCOMPRESSION MEMBEW 81 B-3.1 Pedestals and Short Columns with Lateral ‘Des 81 B-3.2 Short Columns with Helical Reinforcement 81 B-3.3 Long Columns 81 B-3.4 Composite Columns 81 9
  • IS 456 : 2ooo B-4 MYERS SUBJECTED TOCOMBINED Axw. LOAD BENDING AND 83 B-4.1 Design Based on Untracked Section 83 B-4.2 Design Based on Cracked Section 83 B-43 Members Subjected to Combined Direct Load and Flexure 83 B-5 SHEAR 83 B-5.1 Nominal Shear Stress 83 B-5.2 Design Shear Strength of Concrete 84 B-5.3 Minimum Shear Reinforcement 85 B-5.4 Design of Shear Reinforcement 85 B-5.5 Enhanced Shear Strength of Sections Close to Supports 85 B -6 TORSION 86 B-6.1 General 86 B-6.2 Critical Section 86 B-6.3 Shear and Torsion 86 B-6.4 Reinforcement in Members Subjected to Torsion 86ANNEX C CALCULATION OF DEFLECTION 88 C-l TOTAL DEFLECTION 88 C-2 SHORT-TERM DEFLECTION 88 C-3 DEFLECI-ION TOSHRINKAGE DUE 88 C-4 DE-ON DUETOCREEP 89ANNEX D SLABS SPANNING IN TWO DIRECTIONS 90 D-l RESTRAINED SLAIIS 90 D-2 SIMPLY SIJIWRTEDSLABS 90 ANNEX E EFFECTIVE LENGTH OF COLUMNS 92 ANNEX F CALCULATION OF CRACK WIDTH 95 ANNEX G MOMENTS OF RESISTANCE FOR RECTANGULAR AND T-SECTIONS 96 G- 1 RECTANGULAR SECIIONS 96 G- 1.1 Sections without Compression Reinforcement % G- 1.2 Sections with Compression Reinforcement 96 G-2 FLANGED SECTION 96 ANNEX H COMMITTEE COMPOSITION 98 10
  • IS456:2000 SECTION 1 GENERAL1 SCOPE EL - Earthquake loadk-1 This standard deals with the general structural use Es - Modulus of elasticity of steelof plain and reinforced concrete. Eccentricity1.1.1For the purpose of this standard, plain concrete J& - characteristic cube compressivestructures are those where reinforcement, if provided strength of concreteis ignored for~determinationof strength of the structure. xx - Modulus of rupture of concrete (flexural tensile strength)1.2 Special requirements of structures, such as shells,folded plates, arches, bridges, chimneys, blast resistant fa - Splitting tensile strength of concretestructures, hydraulic structures, liquid retaining fd - Design strengthstructures and earthquake resistant structures, covered fY - Characteristic strength of steelin respective standards have not been covered in thisstandard; these standards shall be used in conjunction 4 - Unsupported height of wallwith this standard. Hive- Effective height of wall L - Effective moment of inertia2 REFERENCES zc - Moment of inertia of the gross section excluding reinforcementThe Indian Standards listed in Annex A containprovisions which through reference in this text, 4 - Moment of intertia of cracked sectionconstitute provisions of this standard. At the time of K - Stiffness of memberpublication, the editions indicated were valid. All k - Constant or coefficient or factorstandards are subject to revision and parties to Ld - Development lengthagreements abased on this standard are encouraged to LL- Live load or imposed loadinvestigate the possibility of applying the most recenteditions of the standards indicated in Annex A. Lw - Horizontal distance between centres of lateral restraint3 TERMINOLOGY 1 - Length of a column or beam between adequate lateral restraints or theFor the purpose of this standard, the definitions given unsupported length of a columnin IS 4845 and IS 6461 (Parts 1 to 12) shall generallyapply. Effective span of beam or slab or effective length of column4 SYMBOLS Effective length about x-x axisFor the purpose of this standard, the following letter Effective length about y-y axissymbols shall have the meaning indicated against each, Clear span, face-to-face of supportswhere other symbols are used, they are explained at I’,,for shorter of the two spans at rightthe appropriate place: angles A - Area 4 - Length of shorter side of slab b - Breadth of beam, or shorter dimension Length of longer side of slab of a rectangular column lY - 4 - Distance between points of zero b ef - Effective width of slab moments in a beam bf - Effective width of flange Span in the direction in which 4 - k - Breadth of web or rib moments are determined, centre to D - Overall depth of beam or slab or centre of supports diameter of column; dimension of a Span transverse to I,, centre to centre 12 - rectangular column in the direction of supports under consideration 1’ - 1z for the shorter of the continuous Thickness of flange 2 Df - spans DL - Dead load M - Bending moment d - Effective depth of beam or slab m - Modular ratio d’ - Depth of compression reinforcement n - Number of samples from the highly compressed face P - Axial load on a compression member EC - ModuIus of elasticity of concrete Calculated maximum bearing pressure 4,) - 11
  • IS 456 : 2000 Yc, - Calculated maximum bearing pressure xl - Partial safety factor for material of soil snl - Percentage reduction in moment r - Radius E UC - Creep strain of concrete s - Spacing of stirrups or standard (T - chc Permissible stress in concrete in deviation bending compression T - Torsional moment OLX - Permissible stress in concrete in direct compression t - Wall thickness <T mc - Permissible stress in metal in direct V - Shear force compression W - Total load 0% - Permissible stress in steel in WL - Wind load compression W - Distributed load per unit area % - Permissible stress in steel in tension Wd - Distributed dead load per unit area 0,” - Permissible tensile stress in shear reinforcement WI - Distributed imposed load per unit area Design bond stress X - Depth of neutral axis Shear stress in concrete z - Modulus of section Maximum shear stress in concrete Z - Lever arm with shear reinforcement OZ, - B Angle or ratio Nominal shear stress r, - Partial safety factor for load Diameter of bar 12
  • IS456:2000 SECTION 2 MATERIALS, WORKMANSHIP, INSPECTION AND TESTING5 MATERIALS have no relation whatsoever with the characteristics guaranteed by the Quality Marking as relevant to that5.1 Cement cement. Consumers are, therefore, advised to go byThe cement used shall be any of the following and the the characteristics as given in the correspondingtype selected should be appropriate for the intended Indian Standard Specification or seek specialistuse: advise to avoid any problem in concrete making and a) 33 Grade ordinary Portland cement construction. conforming to IS 269 5.2 Mineral Admiitures b) 43 Grade ordinary Portland cement conforming to IS 8 112 5.2.1 Poz.zolanas 53 Grade ordinary Portland cement Pozzolanic materials conforming to relevant Indian c) conforming to IS 12269 Standards may be used with the permission of the engineer-in-charge, provided uniform blending with d) Rapid hardening Portland cement conforming cement is ensured. to IS 8~041 Portland slag cement conforming to IS 455 Fly ash (pulverizedfuel ash) e) Portland pozzolana cement (fly ash based) FIy ash conforming to Grade 1 of IS 3812 may be f) conforming to IS 1489 (Part 1) use?, as part replacement of ordinary Portland cement provided uniform blending with cement is ensured. g) Portland pozzolana cement (calcined clay based) conforming to IS 1489 (Part 2) Silicafume h) Hydrophobic cement conforming to IS 8043 Silica fume conforming to a standard approved by the j) Low heat Portland cement conforming to deciding authority may be used as part replacement of IS 12600 cement provided uniform blending with the cement is ensured. k) Sulphate resisting Portland cement NOTE-The silica fume (very fine non-crystalline silicon conforming to IS 12330 dioxide)is a by-product the manufactmeof silicon, kmxilicon ofOther combinations of Portland cement with mineral or the like, from quartzand carbon in electric arc furnace. It is usually usedinpropoltion of 5’m lOpercentofthecementconbcntadmixtures (see 5.2) of quality conforming with of a mix.relevant Indian Standards laid down may also be usedin the manufacture of concrete provided that there are Rice husk ashsatisfactory data on their suitability, such as Rice husk ash giving required performance andperformance test on concrete containing them. uniformity characteristics -may be used with the5.1.1 Low heat Portland cement conforming to approval of the deciding authority.IS 12600 shall be used with adequate precautions with NOTE--Rice husk ash is produced by burning rice husk andregard to removal of formwork, etc. contain large propotion of silica. To achieve amorphousstate,5.1.2 High alumina cement conforming to IS 6452 or rice husk may be burntat controlledtemperatum.It is necessary to evaluatethe productfrom a ptuticularsource for performnncesupersulphated cement conforming to IS 6909 may be and uniformitysince it can range from being as dekterious asused only under special circumstances with the prior silt when incorporatedin concmte. Waterdemnnd and dryingapproval of the engineer-in-charge. Specialist literature &i&age should be studied before using ria husk.may be consulted for guidance regarding the use of 5.2.u iuetakaolinethese types of cements. Metakaoline having fineness between 700 to 5.1.3 The attention of the engineers-in-charge and 900 m?/kg may be used as ~pozzolanic material in users of cement is drawn to the fact that quality of concrete. various cements mentioned in 5.1 is to be determined NOTE-Metaknoline is obtained by calcination of pun or on the basis of its conformity to the performance r&ledkaolinticclnyatatempexatumbetweea6soVand8xPc characteristics given in the respective Indian Standard followed by grind& to achieve a A of 700 to 900 n?/kg. Specification for thatcement. Any trade-mark or any The resultingmaterialhas high pozzolanicity. trade name indicating any special features not covered in the standard or any qualification or other special 5.2.2 Ground Granulated Blast Furnace Slag performance characteristics sometimes claimed/ Ground granulated blast furnace slag obtained by indicated on the bags or containers or in advertisements grinding granulated blast furnace slag conforming to alongside the ‘Statutory Quality Marking’ or otherwise IS 12089 may be used as part replacement of ordinary 13
  • IS 456 : 2000Portland cements provided uniform blending with free from injurious amounts of oils, acids, alkalis, salts,cement is ensured. sugar, organic materials or other substances that may be deleterious to concrete or steel.5.3 Aggregates Potable water is generally considered satisfactoryAggregates shall comply with the requirements of for mixing concrete. As a guide the followingIS 383. As far as possible preference shall be given to concentrations represent the maximum permissiblenatural aggregates. values:5.3.1 Other types of aggregates such as slag and a) To neutralize 100 ml sample of water, usingcrushed overbumt brick or tile, which may be found phenolphthalein as an indicator, it should notsuitable with regard to strength, durability of concrete require more than 5 ml of 0.02 normal NaOH.and freedom from harmful effects may be used for plain The details of test are given in 8.1 of ISconcrete members, but such aggregates should not 3025 (Part 22).contain more than 0.5 percent of sulphates as SO, and b) To neutralize 100 ml sample of water, usingshould not absorb more than 10 percent of their own mixed indicator, it should not require moremass of water. than 25 ml of 0.02 normal H$O,. The details of ‘test shall be as given in 8 of IS 30255.3.2 Heavy weight aggregates or light weight (Part 23).aggregates such as bloated clay aggregates and sinteredfly ash aggregates may also be used provided the cl Permissible limits for solids shall be as givenengineer-in-charge is satisfied with the data on the in Table of concrete made with them. 5.4.1 In case of doubt regarding development of NOTE-Some of the provisions of the code would require strength, the suitability of water for making concrete moditicationwhen these aggnzgates used;specialistlitemtute are shall be ascertained by the compressive strength and may be consulted for guidance. initial setting time tests specified in and Size of Aggregate The sample of water taken for testing shall represent the water proposed to be used for concreting,The nominal maximum size of coarse aggregate should due account being paid to seasonal variation. Thebe as large as possible within the limits specified but sample shall not receive any treatment before testingin no case greater than one-fourth of the minimum other than that envisaged in the regular supply of waterthickness of the member, provided that the concrete proposed for use in concrete. The sample shall be storedcan be placed without difficulty so as to surround all in a clean container previously rinsed out with similarreinforcement thoroughly and fill the comers of the water.form. For most work, 20 mm aggregate is suitable. S.4.1.2 Average 28 days compressive strength of atWhere there is no restriction to the flow of concrete least three 150 mm concrete cubes prepared with waterinto sections, 40 mm or larger size may be permitted. proposed to be used shall not be less than 90 percentIn concrete elements with thin sections, closely spaced of the average of strength of three similar concretereinforcement or small cover, consideration should be cubes prepared with distilled water. The cubes shallgiven to the use of 10 mm nominal maximum size. be prepared, curedand tested in accordance with thePlums above 160 mm and up to any reasonable size requirements of IS 5 16.may be used in plain concrete work up to a maximum The initial setting time of test block made withlimit of 20 percent by volume of concrete when theappropriate cement and the water proposed to bespecifically permitted by the engineer-in-charge. The used shall not be less than 30 min and shall not differplums shall be distributed evenly and shall be not closer by& 30min from the initial setting time of controlthan 150 mm from the surface. test block prepared with the same cement and distilled5.3.3.1 For heavily reinforced concrete members as water. The test blocks shall be preparedand tested inin the case of ribs of main beams, the nominal accordance with the requirements off S 403 1 (Part 5).maximum size of the aggregate should usually be 5.4.2 The pH value of water shall be not less than 6.restricted to 5 mm less than the minimum clear distancebetween the main bars or 5 mm less than the minimum 5.4.3 Sea Watercover to the reinforcement whichever is smaller. Mixing or curing of concrete with sea water is not 5.3.4 Coarse and fine aggregate shall be batched recommended because of presence of harmful salts in separately. All-in-aggregate may be used only where sea water. Under unavoidable circumstances sea water specifically permitted by the engineer-in-charge. may be used for mixing or curing in plain concrete with no embedded steel after having given due consideration 5.4 Water to possible disadvantages and precautions including use Water used for mixing and curing shall be clean and of appropriate cement system. 14
  • lS456:2000 ‘lhble 1 Permissible Limit for !Wids (claust? 5.4)SI -apu Permb?dbleLImlt,No. Maxi) organic IS 3a25 (Pal-l18) 2(Jomgllii) Inorganic IS 3025 (yalt 18) 3ooomo/Liii) Sulphaki (us SOJ IS302s(Part24) amo/liv) Chlorides (as Cl) IS 3025 (part 32) 2ooompll for fxmaetc not Containing embcd~sti mdsoomg/l for leInfolced collcntc worlrv) Suspfmdedmatter IS 3025 (Palt 17) 2(xJom%l5.4.4 Water found satisfactory for mixing is also 5.6.1 All reinforcement shall be free from loose millsuitable for curing concrete. However, water used for scales, loose rust and coats of paints, oil, mud or anycuring should not produce any objectionable stain or other substances which may destroy or reduce bond.unsightly deposit on the concrete surface. The presence Sand blasting or other treatment is recommended toof tannic acid or iron compounds is objectionable. clean reinforcement. 5.6.2 Special precautions like coating of reinforcement5.5 Admixtures may be required for reinforced concrete elements in5.5.1 Admixture, if used shall comply with IS 9103. exceptional cases and for~rehabilitation of structutes.Previous experience with and data on such materials Specialist literature may be referred to in such cases.should be considered in relation to the likely standa& of 5.6.3 The modulus of elasticity of steel shall be takensupervisionand workmanshipto the work being specified, as 200 kN/mm*. The characteristic yield strength of55.2 Admixtures should not impair durability of different steel shall be assumed as the minimum yieldconcrete nor combine with the constituent to form stress/O.2percent proof stress specified in the relevantharmful compounds nor increase the risk of corrosion Indian Standard.of reinforcement. 5.7 Storage of Materials55.3 The workability, compressive strength and theslump loss of concrete with and without the use of Storage of materials shall be as described in IS 4082.admixtures shall be established during the trial mixes 6 CONCRETEbefore use of admixtures.5.5.4 The relative density of liquid admixtures shall 6.1 Gradesbe checked for each drum containing admixtures and The concrete shall be in grades designated as percompared with the specified value before acceptance. Table The chloride content of admixtures shall 6.1.1 The characteristic strength is defined as thebe independently tested for each batch before strength of material below which not more thanacceptance. 5 percent of the test results are expectedto fall.5.5.6 If two or more admixtures are used 6.1.2 The minimum grade of concrete for plain andsimultaneously in the same concrete mix, data should reinforced concrete shall be as per Table obtained to assess their interaction and to ensure 61.3 Concrete of grades lower than those given intheir compatibility. Table-5 may be used for plain concrete constructions, 5.6 -Reinforcement lean concrete, simple foundations, foundation for masonry walls and other simple or temporary The reinforcement shall be any of the following: reinforced concrete construction. 4 Mild steel and medium tensile steel bars conforming to IS 432 (Part 1). 6.2 Properties of Concrete b) High strength deformed steel barsconforming 63.1 Increase of Strength with Age to IS 1786. There is normally a gain of strength beyond 28 days. cl Hard-drawn steel wire fabric conforming to The quantum of increase depends upon the grade and IS 1566. type of cement, curing and environmental conditions, 4 Structural steel conforming to Grade A of etc. The design should be based on 28 days charac- IS 2062. teristic strength of concrete unless there is a evidence to 15
  • IS 456 : 2000 Table 2 Grades cif Concrete (Clau.re6.1,9.2.2, 15.1.1 and36.1) whereGroup Grade Designation SpecifiedCharacte~tk E, is the short term static modulus of elasticity in Compressive Streng$b of 150 mm Cube at 28 Days in N/mm*. N/mmz Actual measured values may differ by f 20 percent (1) (2) (3) from the values dbtained from the above expression.Ordinary M 10 10Concrete M 15 6.2.4 Shrinkage 15 M 20 20 The total shrinkage of concrete depends upon theStandard M 25 25 constituents of concrete, size of the member andConcrete M 30 30 environmental conditions. For a given humidity and M 35 35 temperature, the total shrinkage of concrete is most M40 40 M 45 45 influenced by the total amount of water present in the M JO 50 concrete at the time of mixing and, to a lesser extent, M 55 55 by the cement content.High M60 60 In the absence of test data, the approximateStrength M65 65Concrete M70 70 value of the total shrinkage strain for design may be M75 75 taken as 0.000 3 (for more information, see-IS 1343). M 80 80 NOTES 6.2.5 Cmep of Concrete 1 In the designationof concrete mix M mfm to the mix and the number to the specified compressive strengthof 150 mm size Creep of concrete depends,in addition to the factors cube at 28 days, expressed in N/mn?. listed in 6.2.4, on the stress in the concrete, age at 2 For concreteof compressivestrength greata thanM 55, design loading and the duration of loading. As long as the parametersgiven in the stand& may not be applicable and the stress in concrete does not exceed one-third of its values may be obtoined from specialized literatures and characteristic compressive strength, creep may be experimentalresults. assumed to be proportional to the stress.justify a higher strength for a particular structure due to 6.25.11n the absence of experimental data and detailedage. information on the effect of the variables, the ultimate6.2.1.1 For concrete of grade M 30 and above, the creep strain may be estimated from the followingrateof increase of compressive strength with age shall values of creep coefficient (that is, ultimate creep strain/be based on actual investigations. elastic strain at the age of loading); for long span structure, it is advisable to determine actual creep6.2.1.2 Where members are subjected to lower direct strain, likely to take place:load during construction, they should be checked forstresses resulting from combination of direct load and Age at Loading Creep Coeficientbending during construction. 7 days Tensile Strength of Concrete 28 days 1.6The flexural and splitting tensile strengths shall be 1 year 1.1obtained as described in IS 516 and IS 5816 NOTE-The ultimatecreepstrain,estimatedas described aboverespectively. When the designer wishes to use an does not include the elastic strain.estimate of the tensile strength from the compressivestrength, the following formula may be used: 6.2.6 Thermal Expansion Flexural strength, f, = 0.7.& N/mm2 The coefficient df thermal expansion depends on nature of cement, the aggregate, the cement content, thewheref& is the characteristic cube compressive strength relative humidity and the size of sections-The valueof concrete in N/mmz. of coefficient of thermal expansion for concrete with6.2.3 Elastic Deformation different aggregates may be taken as below:The modulus of elasticity is primarily influenced by npe of Aggregate Coeficient of Thermalthe elastic properties of the aggregate and to a lesser Expansion for CommtePCextent by the conditions of curing qd age of the Quartzite 1.2 to 1.3 x 10-Sconcrete, the mix proportions and the type of cement.The modulus of elasticity is normally related to the Sandstone 0.9 to 1.2 x 1cPcompressive strength of concrete. Granite 0.7 to 0.95 x 10-J Basalt O.% 0.95 x lo5 to6.2.3.1 The modulus of elasticity of concrete can be Limestone 0.6 t@.9 x 10sassumed as follows: 16
  • IS 456 : 20007 WORKABILITY OF CONCRETE7.1 The concrete mix proportions chosen should be be compacted with the means available. Suggestedsuch that the concrete is of adequate workability for ranges of workability of concrete measured inthe placing conditions of the concrete and can properly accordance with IS 1199 are given below: Placing Conditions Degree of Slump Workability (mm) (1) (2) (3)Blinding concrete; Very low See 7.1.1Shallow sections;Pavements using pavers IMass concrete; Low 25-75Lightly reinforcedsections in slabs,beams, walls, columns;Floors;Hand placed pavements;Canal lining;Strip footingsHeavily reinforced Medium 50-100sections in slabs,beams, walls, columns; 75-100Slipform work;Pumped concrete 1Trench fill; High 100-150In-situ pilingTremie concrete I Very high See 7.1.2 NOTE-For most of the placing conditions, internal vibrators (needle vibrators) are suitable. The diameter of tbe needle shall be determined based on the density and spacing of reinforcement bars and thickness of sections. For tremie concrete, vibrators am not rewired to be used (see &SO 13.3).7.1.1 In the ‘very low’ category of workability where a suitably low permeability is achieved by having anstrict control is necessary, for example pavement adequate cement content, sufficiently low free water/quality concrete, measurement of workability by cement~ratio,~byensuring complete compaction of thedetermination of compacting factor will be more concrete, and by adequate curing.appropriate than slump (see IS 1199) and a value of The factors influencing durability include:compacting factor of 0.75 to 0.80 is suggested. 7.1.2 In the ‘very high’ category of workability, 4 the environment;measurement of workability by determination of flow b) the cover to embedded steel;will be appropriate (see IS 9103). cl the typeand_quality of constituent materials;8 DURABILITY OF CONCRETE 4 the cement content and water/cement ratio of8.1 General the concrete;A durable concrete is one that performs satisfactorily d workmanship, to obtain full compaction andin the working environment during its anticipated efficient curing; andexposure conditions during service. The materials andmix proportions specified and used should be such as f) the shape and size of the maintain its integrity and, if applicable, to protect The degree of exposure anticipated for the concreteembedded metal from corrosion. during its service life together with other relevant8.1.1 One of the main characteristics influencing the factors relating to mix composition, workmanship,durability of concrete is its permeability to the ingress design and detailing should be considered. The of water, oxygen, carbon dioxide, chloride, sulphate and concrete mix to provide adequate durability under these other potentially deleterious substances. Impermeability conditions should be chosen taking account of the is governed by the constituents and workmanship used accuracy of current testing regimes for control andin making the concrete. with normal-weight aggregates compliance as described in this standard. 17
  • IS 456 : 20008.2 Requirements for Durability Abrasive8.2.1 Shape and Size of Member Specialist literatures may be referred to for durabilityThe shape or design details of exposed structures requirementsof concrete surfaces exposed to abrasiveshould be such as to promote good drainage of water action,for example, in case of machinery and metal tyres.and to avoid standing pools and rundown of water. Freezing and thawingCare should also be taken to minimize any cracks thatmay collect or transmit water. Adequate curing is Where freezing and thawing actions under wetessential to avoid the harmful effects of early loss of conditions exist, enhanced durability can be obtainedmoisture (see 13S).Member profiles and their by the use of suitable air entraining admixtures. Whenintersections with other members shall be designed and concrete lower than grade M 50 is used under thesedetailed in a way to ensure easy flow of concrete and conditions, the mean total air content by volume ofproper compaction during concreting. the fresh concrete at the time df delivery into the construction should be:Concrete is more vulnerable to deterioration due tochemical or climatic attack when it is in thin sections, Nominal Maximum Size Entrained Airin sections under hydrostatic pressure from one side Aggregate Percentageonly, in partially immersed sections and at corners andedges of elements. The life of the strycture can be WWlengthened by providing extra cover to steel, by 20 5flchamfering the corners or by using circular cross- 40 4flsections or by using surface coatings which prevent orreduce the ingress of water, carbon dioxide or Since air entrainment reduces the strength, suitableaggressive chemicals. adjustments may be made in the mix design for8.2.2 Exposure Conditions achieving required strength. General environment Exposure to sulphate attackThe general environment tc, which the concrete will Table 4 gives recommendations for the type of cement,be exposed during its working life is classified into maximum free water/cement ratio and minimumfive levels of severity, that is, mild, moderate, severe, cement content, which are required at different sulphatevery severe and extreme as described in Table 3. concentrations in near-neutral ground water having Table 3 Environmental Exposure Conditions pHof6to9. (Chwes and 35.3.2) For the very high sulphate concentrations in Class 5 conditions, some form of lining such as polyethyleneSl No. Environment Exposure Conditions or polychloroprene sheet; or surface coating based on(1) (2) (3) asphalt, chlorinated rubber, epoxy; or polyurethanei) Mild Concrete surfaces protected against materials should also be used to prevent access by the weatheror aggressiveconditions,except those situatedin coastal area. sulphate solution.ii) Moderate Concretesurfaces shelteredfrom severe rain or freezing whilst wet 8.2.3 Requirement of Concrete Cover Concrete exposedto condensation rain and The protection of the steel in concrete against Concretecontinuously underwater corrosion depends upon an adequate thickness of good Concretein contact or buriedundernon- quality concrete. aggressive soil/groundwater Concrete surfaces sheltered from The nominal cover to the reinforcement shall saturatedsalt air in coastal area be provided as per 26.4. iii) Severe Concrete surfaces exposed to severe rain, alternate wetting and drying or 0.2.4 Concrete Mix Proportions occasional freezing whilst wet or severe condensation. General Concletecompletelyimmrsedinseawnter The free water-cement ratio is an important factor in Concreteexposed to coastalenvironment governing the durability of concrete and should always iv) Very severe Concrete surfaces exposed to sea water spray,corrosivefumes or severe freezing be the lowest value. Appropriate values for minimum conditions whilst wet cement content and the maximum free water-cement Concrete in contact with or buried ratio are given in Table 5 for different exposure underaggressive sub-soil/groundwater conditions. The minimum cement content and -4 Extreme Surfaceof membersin tidal zone maximum water-cement ratio apply to 20 mm nominal Members in direct contact with liquid/ maximum size aggregate. For other sizes of aggregate solid aggressive chemicals they should be changed as given in Table 6. 18
  • IS 456 : 20008.2.4.2 Maximum cement content been given in design to the increased risk of crackingCement content not including fly ash and ground due to drying shrinkage in.thin sections, or to earlygranulated blast furnace slag in excess of 450 kg/x$ thermal cracking and to the increased risk of damageshould not be used unless special consideration has due to alkali silica reactions. Table 4 Requirements for Concrete Exposed to Sulphate Attack (Clauses and 9.1.2)SI ChSS Concentration of Sulphates, Type ofCement Dense, Fully Compacted concrete.No. Expressed a~ SO, Made with 20 mm Nominal r . Maximum Size Aggregates In Soil Complying with IS 383 Total SO, SO,in In Ground r . 2:l water: Water Soil Extract Minimum Maximum Cement Face Water- Content Cement ~kg/m’ Ratio &d @ (1) (2) (3) (4) (5) (6) (7) (8) 0 1 TraCeS Less than LesSthan Ordinary Portland 280 0.55 (< 0.2) 1.0 0.3 cement or Portland slag cement or Portland pozzolana cement ’ ii) 2 0.2 to 1.oto 0.3 to Ordinary Portland 330 0.50 0.5 1.9 1.2 cement or Portland slag cement or Portland pozzolana cement Supersulphated 310 0.50 cement or sulphate resisting Portland cement iii) 3 0.5 to 1.9 to 1.2 to Supersulphated 330 0.50 1.0 3.1 2.5 cement or sulphate resisting Portland cement Portland pozzolana 350 0.45 cement or Podand slag cement iv) 4 1.0to 3.1 to 2.5 to Supersulphated 370 0.45 2.0 5.0 5.0 or sulphate resisting Portland cement v) 5 More than More than More than Sulphate resisting 400 0.40 2.0 5.0 5.0 Portland cement or superrulphated cement with protective coatingsNOTES 1 Cement content given in this table is irrespective of grades of cement.2 Use of supersulphated cement is generally restricted where the prevailing temperature is above 40 “c.3 Supersulphated cement gives~an acceptable life provided that the concrete is dense and prepared with a water-cement mtio of 0.4 or less, in mineral acids, down to pH 3.5. 4 The cement contents given in co1 6 of this table are the minimum recommended. For SO, contents near tbe upper limit of any class, cement contents above these minimum are advised. 5 For severe conditions, such as thin sections under hydrostatic pressure on one side only and sections partly immersed, considerations should be given to a further reduction of water-cement ratio. 6 Portland slag cement conforming to IS 455 with slag content more than 50 percent exhibits better sulphate resisting properties. 7 Where chloride is encountered along with sulphates in soil or ground water, ordinary Portland cement with C,A content from 5 to 8 percent shall be desirable to be used in concrete, instead of sulphate resisting cement. Alternatively, Portland slag cement conforming to IS 455 having more than 50 percent slag or a blend of ordinary Portland cement and slag may be used provided sufficient information is available on performance of such blended cements in these conditions. 19
  • IS 456 : 20008.2.5 Mix Constituents expansion and disruption of concrete. To prevent this, the total water-soluble sulphate content of the concrete8.2.5.1 General mix, expressed as SO,, should not exceed 4 percent byFor concrete to be durable, careful selection of the mix mass of the cement in the mix. The sulphate contentand materials is necessary, so that deleterious should be calculated as the total from the variousconstituents do not exceed the limits. constituents of the mix. The 4 percent limit does not apply to concrete made8.2.5.2 Chlorides in concrete with supersulphated cement complying with IS 6909.Whenever there is chloride in concrete there is an Alkali-aggregate reactionincreased risk of corrosion of embedded metal. Thehigher the chloride content, or if subsequently exposed Some aggregates containing particular varieties ofto warm moist conditions, the greater the risk of silica may be susceptible to attack by alkalis (N%Ocorrosion. All constituents may contain chlorides and and %O) originating from cement or other sources,concrete may be contaminated by chlorides from the producing an expansive reaction which can causeexternal environment. To minimize the chances of cracking and disruption of concrete. Damage todeterioration of concrete from harmful chemical salts, concrete from this reaction will normally only occurthe levels of such harmful salts in concrete coming when .a11 following are present together: thefrom concrete materials, that is, cement, aggregates a) A high moisture level, within the concrete;water and admixtures, as well as by diffusion from the b) A cement with high alkali content, or anotherenvironment should be limited. The total amount of source of alkali;chloride content (as Cl) in the concrete at the time ofplacing shall be as given in Table 7. c) Aggregate containing an alkali reactive constituent.The total acid soluble chloride content should becalculated from the mix proportions and the measured Where the service records of particular cement/chloride contents of each of the constituents. Wherever aggregate combination are well established, and do not -possible, the total chloride content of the concrete include any instances of cracking due to alkali-should be determined. aggregate reaction, no further precautions should be necessary. When the materials are unfamiliar, Sulphates in concrete precautions should take one or more of the followingSulphates are present in most cements and in some forms:aggregates; excessive amounts of water-solublesulphate from these or other mix constituents can cause a) Use of non-reactive aggregate from alternate sources. Table 5 Minimum CementContent, Maximum Water-Cement Ratio and Minimum Grade of Concrete for Different Exposures with Normal Weight Aggregates of 20 mm Nominal Maximum Size (Clauses 6.1.2, and9.1.2)SI Exposure Plain Concrete Reinforced ConcreteNo. / - * - Minimum Maximum Minimum Minimum Maximum Minimum Cement Free Water- Grade of Cement Free Water- Grade of Content Cement Ratio Concrete’ Content Cement Ratio Concrete kg/m’ kg/m’ 1) (2) (3) (4) (5) (6) (7) 0-9 0 Mild 220 0.60 300 0.55 M 20 iii) Moderate 240 0.60 M 15 300 0.50 M 25 iii) Severe 250 0.50 M 20 ~320 0.45 M 30 iv) Very severe 260 0.45 M 20 340 0.45) M 35 v) Extreme 280 0.40 M25 360 0.40 M40 NOTES 1 Cement content prescribed in this table is irrespective of the grades of cement and it is inclusive of ad&ons mentioned in 5.2. The additions such as fly ash or ground granulated blast furnace slag may be taken into account in the concrete composition with respect to Ihe cement content and water-cement ratio if the suitability is established and as long as the maximum amounts taken into account do not exceed the limit of pozzolona and slag specified in IS 1489 (Part I) and IS 455 respectively. 2 Minimum gradefor plain concrete under mild exposure condition is not specified. 20
  • IS456: 2000 Table 6 Adjustments to Minimum Cement evaporation may cause serious concentrations of salts Contents for Aggregates Other Than 20 mm with subsequent deterioration, even where the original Nominal Maximum Size salt content of the soil or water is not high. (Clause NOTE- Guidanceregarding requirements conctt%c for exposed Adjustmenk to Minimum Cement to sulphatenttackis given in Nominal MaximumNo. Aggregate Size Contents in Table 5 Drainage mm Wm’(1) (2) (3) At sites where alkali concentrations are high or mayi) 10 +40 become very high, the ground water should be loweredii) 20 0 by drainageso that it will not come into direct contactiii) 40 -30 with the concrete. Additional protection may be obtained by the use of Tabie 7 Limits of Chloride Content of Concrete chemically resistant stone facing or a layer of plaster (Clause of Paris covered with suitable fabric, such as jute thoroughly impregnated with bituminous material.SI Type or Use of Concrete Maximum TotalNo. Acid Soluble 8.2.7 Compaction, Finishing and Curing Chloride Content Expressed as k&n’ of Adequate compaction without segregation should be concrete ensured by providing suitable workability and by(1) (2) (3) employing appropriate placing and compactingi) Concrete containing metal and 0.4 equipment and procedures. Full compaction is steam cured nt elevated tempe- particularly important in the vicinity of construction rntureand pre-stressedconcreteii) Reinforced conctite or plain concrete 0.6 and movement joints and of embedded water bars and containing embedded metal reinforcement.iii) Concretenot containingembedded 3.0 Good finishing practices are essential for durable metal or any materialquiring concrete. protectionfrom chloride Overworking the surface and the addition of water/ cement to aid in finishing should be avoided; the b) Use of low alkali ordinary ‘Portland cement resulting laitance will have impaired strength and having total alkali content not more than 0.6 durability and will be particularly vulnerable to percent~(as Na,O equivalent). freezing and thawing under wet conditions. Further advantage can be obtained by use of fly It is essential to use proper and adequate curing ash (Grade 1) conforming to IS 3812 or techniques to reduce the permeability of the concrete granulated blastfurnace slag conforming to and enhance its durability by extending the hydration IS 12089 as part replacement of ordinary of the cement, particularly in its surface zone Portland cement (having total alkali content as (see 13.5). Na,O equivalent not more than 0.6 percent), provided fly ash content is at least 20 percent 8.2.8 Concrete in Sea-water or slag content is at least 50 percent. Concrete in sea-water or exposed directly along the c) Measures to reduce the degree of saturation of sea-coast shall be at least M 20 Grade in the case of the concrete during service such as use of plain concrete and M 30 in case of reinforced concrete. impermeable membranes. The use of slag or pozzolana cement~is advantageous d) Limitingthe cement content in the concrete mix under such conditions. and thereby limiting total alkali content in the Special attention shall be. given to the design concrete mix. For more guidance specialist of the mix to obtain the densest possible concrete; slag, literatures may be referred. broken brick, soft limestone, soft sandstone, or other porous or weak aggregates shall not be used. 8.2.6 Concrete in Aggressive Soils and Water As far as possible, preference shall be given to General precast members unreinforced, well-cured and The destructive action of aggressive waters on concrete hardened, without sharp comers, and having trowel- is progressive. The rate of deterioration decreases as smooth finished surfaces free from crazing, cracks or the concrete~is made stronger and more impermeable, other defects; plastering should be avoided. and increases as the salt content of the water increases. No construction joints shall be allowed within Where structures are only partially immersed or are in 600 mm below low water-level or within 600 mm of contact with aggressive soils or waters on one side only, the upper and lower planes of wave action. Where 21
  • IS 456 : 2000unusually severe conditions or abrasion’are anticipated, a) 5pe ofwpga%such parts of the work shall be protected by bituminous b) Maximum cement content, andor silica-fluoride coatings or stone facing bedded with c) Whether an admixture shall or shall not bebitumen. used and the type of admixture and the8.2.8.4 In reinforced concrete structures, care shall be condition of use.taken to protect the reinforcement from exposure tosaline atmosphere during storage, fabrication and use. 9.2 Design Mix ConcreteIt may be achieved by treating the surface of 9.2.1 As the guarantor of quality of concrete used inreinforcement with cement wash or by suitable the construction, the constructor shall carry out the mixmethods. design and the mix so designed (not the method of9 CONCRETE MIX PROPORTIONING design) shall be approved by the employer within the limitations of parameters and other stipulations laid9.1 Mix Proportion down by this standard.The mix proportions shall be selected to ensure the 9.2.2 The mix shall be designed to produce the gradeworkability of the fresh concrete and when concrete is of concrete having the required workability and ahardened, it shall have the required strength, durability characteristic strength not less than appropriate valuesand surface finish. given in Table 2. The target mean strength of concrete9.1.1 The determination of the proportions of cement, mix should be equal to the characteristic strength plusaggregates and water to attain the required strengths 1.65 times the standard deviation.shall be made as follows: 9.2.3 Mix design done earlier not prior to one year a) By designing the concrete mix; such concrete may be considered adequate for later work provided shall be called ‘Design mix concrete’, or there is no change in source and the quality of the materials. b) By adopting nominal concrete mix; such concrete shall be called ‘Nominal mix concrete’. 9.2.4 Standard DeviationDesign mix concrete is preferred to nominal mix. If The standard deviation for each grade of concrete shalldesign mix concrete cannot be used for any reason on be calculated, separately.the work for grades of M 20 or lower, nominal mixes Standard deviation based on test strength ofmay be used with the permission of engineer-in-charge, samplewhich, however, is likely to involve a higher cementcontent. a) Number of test results of samples-The total number of test strength of samples required to9.1.2 Information Required constitute an acceptable record for calculationIn specifying a particular grade of concrete, the of standard deviation shall be not less than 30.following information shall be included: Attempts should be made to obtain the 30 samples, as early as possible, when a mix is used 4 Type of mix, that is, design mix concrete or nominal mix concrete; for the first time. b) Grade designation; b) In case of si&icant changes in concrete- When significant changes are made in the cl Type of cement; production of concrete batches (for example 4 Maximum nominal size of aggregate; changes in the materials used, mix design. e) Minimum cement content (for design mix equipment Dr technical control), the standard concrete); deviation value shall be separately calculated for such batches of concrete. 0 Maximum water-cement ratio; g) Workability; cl Standard deviation to be btvught up to date- The calculation of the standard deviation shall h) Mix proportion (for nominal mix concrete); be brought up to date after every change of mix 9 Exposure conditions as per Tables 4 and 5; design. k) Maximum temperature of concrete at the time Assumed stanaianl deviation of placing; Where sufficient test results for a particular grade of m>Method of placing; and concrete are not available, the value of standard n>Degree of supervision. deviation given in Table 8 may be assumed for design of mix in the first instance. As soon as the results of In appropriate circumstances, the following samples are available, actual calculated standard additional information may be specified: deviation shall be used and the mix designed properly. 22
  • IS 456 : 2000However, when adequate past mcords for a similar grade 10 PRODUCTION OF CONCRETEexist andjustify to the designera valueof standarddeviationd&rent from that shown in Table 8, it shallbe pem&ible 10.1 Quality Assurance MeasurestOllSthZltValue. 10.1.1 In order that the properties of the completed structure be consistent with the requirements and the Table 8 Assumed Standard Deviation (Clause and Table 11) assumptions made during the planning and the design, adequate quality assurance measures shall be taken. Grade of AssumedStnndard The construction should result in satisfactory strength, concrete Deviation N/IlUlI* serviceability and long term durability so as to lower the overall life-cycle cost. Quality assurance in M 10 3.5 M 15 1 construction activity relates to proper design, use of adequate materials and components to be supplied by M20 4.0 M 25 I the producers, proper workmanship in the execution of works by the contractor and ultimately proper care M 30 M 35 during the use of structure including timely M40 1 5.0 maintenance and repair by the owner. M45 10.1.2 Quality assurance measures are both technical MS0 ) and organizational. Some common cases should beNOTE-The above values correspond to the site contrdi havingproperstorageof cement;weigh batchingof all materials;controlled specified in a general Quality Assurance Plan whichaddition of ~water;regular checking of all matials. aggregate shall identify the key elements necessary to providegradings and moisture content; and periodical checking of fitness of the structure and the means by which theyworkability and strength.Where there is deviation from the above are to be provided and measured with the overallthe values given in the above table shall be increasedby lN/inm*. purpose to provide confidence that the realized project will work satisfactorily in service fulfilling intended9.3 Nominal Mix Concrete needs. The job of quality control and quality assuranceNominal mix concrete may be used for concrete of would involve quality audit of both the inputs as wellM 20 or lower. The proportions of materials for as the outputs. Inputs are in the form of materials fornominal mix concrete shall be in accordance with concrete; workmanship in all stages of batching,Table 9. mixing, transportation, placing, compaction and9.3.1 The cement content of the mix specified in curing; and the related plant, machinery andTable 9 for any nominal mix shall be proportionately equipments; resulting in the output in the form ofincreased if the quantity of water in a mix has to be concrete in place. To ensure proper performance, it isincrease&o overcome the difficulties of placement and necessary that each step in concreting which will becompaction, so that the water-cement ratio as specified covered by the next step is inspected as the workis not exceeded. proceeds (see also 17). Table 9 Proportions for Nominal Mix-Concrete (Clauses9.3 and 9.3.1)Grade of Total Qua&y of Dry Aggre- Proportion of Fine Quantity of Water perconcrete gates by hhc-per SOkg of &gregate to Coarse 50 kg of Cement, Mar Cement, to be Taken at? the Sum Aggregate (by Mad 1 of the Individual Masses of F’lneand Coarse Aggregates, kg, Max(1) (2) (3) (4)M5 800 Generally 1:2 but subjectto 60M 7.5 625 anupperlimitof 1:1*/sanda 45M 10 480 lower lit of 1:2V, 34M 15 330 32M20 250 30 1 NOTE-The proportionof the fine to coarse aggmgatesshould be adjustedfrom upperlimit to lower limit~progressively the grading as of fine aggregatesbecomes finer and the maximum size of coarse aggregatebecomes larger. Gradedcoarse aggregateshall be used. Exumple For an average grading of tine aggregate (that is. Zone II of Table 4 of IS 383). the proportionsshall be 1:1I/,, I:2 and 1:2’/, for maximum size of aggregates 10 mm, 20 mm and 40 mm respectively. 23
  • IS 456 : 2000 10.1.3 Each party involved in the realization of a measured and within + 3 percent of the quantity of project should establish and implement a Quality aggregate, admixtures and water being measured. Assurance Plan, for its participation in the project. 10.2.3 Proportion/Type and grading of aggregates shall Supplier’s and subcontractor’s activities shall be be made by trial in such a way so as to obtain densest covered in the plan. The individual Quality Assurance possible concrete. All ingredients of the concrete Plans shall fit into the general Quality Assurance Plan. should be used by mass only. A Quality Assurance Plan shall define the tasks and 10.2.4 Volume batching may be allowed only where responsibilities of all persons involved, adequate weigh-batching is not practical and provided accurate control and checking procedures, and the organization bulk densities of materials to be actually-used in and maintaining adequate documentation of the concrete have earlier been established. Allowance for building process and its results. Such documentation bulking shall be made in accordance with IS 2386 should generally include: (Part 3). The mass volume relationship should be 4 test reports and manufacturer’s certificate for checked as frequently as necessary, the frequency for materials, concrete mix design details; the given job being determined by engineer-in-charge b) pour cards for site organization and clearance to ensure that the specified grading is maintained. for concrete placement; N2.5 It is important to maintain the water-cement c) record of site inspection of workmanship, field ratio constant at its correct value. To this end, determi- tests; nation of moisture contents in both fine and coarse d) non-conformance reports, change orders; aggregates shall be made as frequently as possible, the e> quality control charts; and frequency for a given job being determined by the f) statistical analysis. engineer-in-charge according to weather conditions. NOTE-Quality control charts are recommended wherever the The amount-of the added water shall be adjusted to concrete is in continuous production over considerable period. compensate for any observed variationsin the moisture contents. For the determination of moisture content 10.2 Batching in the aggregates, IS 2386 (Part 3) may be referred to. To avoid confusion and error in batching, consideration To allow for the variation in mass of aggregate due to should be given to using the smallest practical number variation in their moisture content, suitable adjustments of different concrete mixes on any site or in any one in the masses of aggregates shall also be made. In the plant. In batching concrete, the quantity of both cement absence of -exact data, only in the case of nominal and aggregate shall be determined by mass; admixture, mixes, the amount of surface water may be estimated if solid, by mass; liquid admixture may however be from the values given in Table 10. measured in volume or mass; water shall be weighed Table 10 Surface Water Carried by Aggregate or measured by volume in a calibrated tank (see also fCZuuse 102.5) IS 4925). SI Aggregate Approximate Quantity of Surface Ready-mixed concrete supplied by ready-mixed No. Water concrete plant shall be preferred. For large and medium F . Percent by Mass l/m3 project sites the concrete shall be sourced from ready- (1) (2) (3 (4) mixed concrete plants or from on site or off site 0 Very wet sand 1.5 120 batching and mixing plants (see IS 4926). ii) Moderately wet sand 5.0 80 10.2.1 Except where it can be shown to the satisfaction iii) Moist sand 2.5 40 of the engineer-in-charge that supply of properly iv) ‘Moist gravel or crashed rock 1.25-2.5 20-40 graded aggregate of uniform quality can be maintained I) Coarser the aggregate, less the water~it will can-y. over a period of work, the grading of aggregate should. be controlled by obtaining the coarse aggregate in 10.2.6 No substitutions in materials used on the work different sizes and blending them in the right or alterations in the established proportions, except as proportions when required, the different sizes being permitted in 10.2.4 and 10.2.5 shall be made without stocked in separate stock-piles. The material should additional tests to show that the quality and strength be stock-piled for several hours preferably a day before of concrete are satisfactory. use. The grading of coarse and fine aggregate should be checked as frequently as possible, the frequency 10.3 Mixing for a given job being determined by the engineer-in- Concrete shall be mixed in a mechanical mixer. The charge to ensure that the specified grading is mixer should comply with IS 179 1 and IS 12 119. The maintained. mixers shall be fitted with water measuring (metering) 10.2.2 The accuracy of the measuring equipment shall devices. The mixing shall be continued until there is a Abewithin + 2 percent of the quantity of cement being uniform distribution of the materials and the mass is 24
  • IS 456 : 2000uniform in colour and c0nsistenc.y. If there is 11.3 Stripping Timesegregation after unloading from the mixer, the Forms shall not be released until the concrete hasconcrete should be remixed. achieved a strength of at least twice the stress to which10.3.1 For guidance, the mixing time shall be at least the concrete may be subjected at the time of removal2 min. For other types of more efficient mixers, of formwork. The strength referred to shall be that ofmanufacturers recommendations shall be followed; concrete using the same cement and aggregates andfor hydrophobic cement it may be decided by the admixture, if any, with the same proportions and curedengineer-in-charge. under conditions of temperature and moisture similar10.3.2 Workability should be checked at frequent to those existing on the work.intervals (see IS 1199). 11.3.1 -Whilethe above criteria of strength shall be the guiding factor for removal of formwork, in normal10.3.3 Dosages of retarders, plasticisers and circumstances where ambient temperature does not fallsuperplasticisers shall be restricted to 0.5,l .Oand 2.0 below 15°Cand where ordinary Portland cement is usedpercent respectively by weight of cementitious and adequate curing is done, following striking periodmaterials and unless a higher value is agreed upon may deem to satisfy the guideline given in 11.3:between the manufacturer and the constructor basedon performance test. Type of Formwork Minimum Period Before Striking11 FORMWORK Formwork11.1 General a) Vertical formwork to columns, 16-24 hThe formwork shall be designed and constructed so walls, beamsas to remain sufficiently rigid during placing andcompaction of concrete, and shall be such as to prevent b) Soffit formwork to slabs 3 days (Props to be refixedloss of slurry from the concrete. For further details immediately after removalregarding design, detailing, etc. reference may be made of formwork)to IS 14687. The tolerances on the shapes, lines anddimensions shown in the~drawing shall be within the cl Sofftt formwork to beams 7 dayslimits given below: (Props to be refixed immediately after removal a) Deviation from specified + 12 of formwork) dimensions of cross-section - 6- 4 Props to slabs: of columns and beams 7 days 1) Spanning up to 4.5 m b) Deviation from dimensions 2) Spanning over 4.5 m 14 days of footings 4 Props to beams and arches: 1) Dimensions in plan + 5omm 1) Spanning up to 6 m 14 days - 12 2) Spanning over 6 m 21 days 2) Eccentricity 0.02 times the width of the foot- For other cements and lower temperature, the ing in the direc- stripping time recommended above may be suitably tion of deviation modified. but not more than 11.3.2 The number of props left under, their sizes and SOmnl disposition shall be such as to be able to safely carry 3) Thickness f 0.05 times the the full dead load of the slab, beam or arch as the case specified thick- may be together with any live load likely to occur ness during curing or further construction.These tolerances apply to concrete dimensions only, and 11.3.3 Where the shape of the element is such that thenot to positioning of vertical reinforcing steel or dowels. formwork has re-entrant angles, the formwork shall be11.2 Cleaning and ‘lhatment of Formwork removed as soon as possible after the concrete has set, to avoid shrinkage cracking occurring due to theAll rubbish, particularly, chippings, shavings and restraint imposed.sawdust shall be removed from the interior of the formsbefore the concrete is placed. The face of formwork 12 ASSEMBLY OF REINFORCEMENTin contact with the concrete shall be cleaned and treatedwith form release agent. Release agents should be 12.1 Reinforcement shall be bent and fixed inapplied so as to provide a thin uniform coating to the accordance with procedure specified in IS 2502. Theforms without coating the reinforcement. high strength deformed steel bars should not be re-bent 25
  • IS 456 : 2000or straightened without the approval of engineer-in- steel bars are bent aside at construction joints andcharge. afterwards bent back into their original positions, careBar bending schedules shall Abeprepared for all should be taken to ensure that at no time is the radiusreinforcement work. of the bend less than 4 bar diameters for plain mild steel or 6 bar diameters for deformed bars. Care shall12.2 All reinforcement shall be placed and maintained also be taken when bending back bars, to ensure thatin the position shown in the drawings by providing the concrete around the bar is not damaged beyondproper cover blocks, spacers, supporting bars, etc. the band.12.2.1 Crossing bars should not be tack-welded for 12.6 Reinforcement should be placed and tied in suchassembly of reinforcement unless permitted by a way that concrete placement be possible withoutengineer-in-charge. segregation of the mix. Reinforcement placing should12.3 Placing of Reinforcement allow compaction by immersion vibrator. Within the concrete mass, different types of metal in contactRough handling, shock loading (prior to embedment) should be avoided to ensure that bimetal corrosion doesand the dropping of reinforcement from a height should not take avoided. Reinforcement should be secured againstdisplacement outside the specified limits. 13 TRANSPORTING, PLACING,12.3.1 Tolerances on Placing of Reinforcement COMPACTION AND CURINGUnless otherwise specified by engineer-in-charge, the 13.1 Transporting and Handlingreinforcement shall be placed within the followingtolerances: After mixing, concrete shall be transported to the formwork as rapidly as possible by methods which will a) for effective depth f 1Omm prevent the segregation or loss of any of the ingredients or less or ingress of foreign matter or water and maintaining b) for effective depth more than f15mm the required workability. 200 mm 13.1.1 During hot or cold weather, concrete shall be123.2 Tolerance for Cover transported in deep containers. Other suitable methods to reduce the loss of water by evaporation in hotUnless specified ~otherwise, actual concrete cover weather and heat loss in cold weather may also beshould not deviate from the required nominal cover adopted.~by +lzmm. 13.2 PlacingNominal cover as given in 26.4.1 should be specified The concrete shall be deposited as nearly as practicableto all steel reinforcement including links. Spacers in its final position to avoid rehandling. The concretebetween the links (or the bars where no links exist) shall be placed and compacted before initial setting ofand the formwork should be of the same nominal size concrete commences and should not be subsequentlyas the nominal cover. disturbed. Methods of placing should be such asSpacers, chairs and other supports detailed on to preclude segregaion. Care should be taken todrawings, together with such other supports as avoid displacement of reinforcement or movementmay be necessary, should be used to maintain the of formwork. As a general guidance, the maxi-specified nominal cover to the steel reinforcement. mum permissible free fall of concrete may be takenSpacers or chairs should be placed at a maximum as 1.5 m.spacing of lm and closer spacing may sometimes benecessary. 13.3 Compaction Spacers, cover blocks should be of concrete of same Concrete should be thoroughly compacted and fully strength or PVC. worked around the reinforcement, around embedded fixtures and into comers of the formwork. 12.4 Welded JoInta or Mechanical Connections 13.3.1 Concrete shall be compacted using mechanical Welded joints or mechanical connections in vibrators complying with IS 2505, IS 2506, IS 2514 reinforcement may be used but in all cases of important and IS 4656. Over vibration and under vibration of connections, tests shall be made to prove that the joints concrete are harmful and should be avoided. Vibration are of the full strength of bars connected. Welding of of very wet mixes should also be avoided. reinforcements shall be done in accordance with the Whenever vibration has to be applied externally, the recommendations of IS 275 1 and IS 9417. design of formwork and the disposition of vibrators 12.5 Where reinforcement bars upto 12 mm for high should receive special consideration to ensure efficient strength deformed steel bars and up to 16 mm for mild compaction and to avoid surface blemishes. 26
  • IS 456 : 200013.4 Construction Joints and Cold Joints of ordinary Portland Cement-and at least 10 days whereJoints are a common source of weakness and, therefore, mineral admixtures or blended cements are used. Theit is desirable to avoid them. If this is not possible, period of curing shall not be less than 10 days fortheir number shall be minimized. Concreting shall be concrete exposed to dry and hot weather conditions.carried out continuously up to construction joints, In the case of concrete where mineral admixtures orthe position and arrangement of which shall be blended cements are used, it is recommended thatindicated by the designer. Construction joints should above minimumperiods may be extended to 14 days.comply with IS 11817. 13.52 Membrane CuringConstruction joints shall be placed at accessible Approved curing compounds may Abeused in lieu oflocations to permit cleaning out of laitance, cement moist curing withthe permission of the engineer-in-slurry and unsound concrete, in order to create rough/ charge. Such compounds shall be applied to all exposeduneven surface. It is recommended to clean out laitance surfaces of the concrete as soon as possible after theand cement slurry by using wire brush on the surface concrete has set. Impermeable~membranes such asof joint immediately after initial setting of concrete polyethylene sheeting covering closely the concreteand to clean out the same immediately thereafter. The surface may also be used to provide effective barrierprepared surface should be in a clean saturated surface against evaporation.dry condition when fresh concrete is placed, against it. 135.3 For the concrete containing Portland pouolanaIn the case of construction joints at locations where cement, Portland slag cement or mineral admixture,the previous pour has been cast against shuttering the period of curing may be increased.recommended method of obtaining a rough surface forthe previously poured concrete is to expose the 13.6 Supervisionaggregate with a high pressure water jet or any otherappropriate means. It is exceedingly difficult and costly to alter concreteFresh concrete should be thoroughly vibrated near once placed. Hence, constant and strict supervision ofconstruction joints so that mortar from the new concrete all the items of the construction is necessary duringflows between large aggregates and develop proper the progress of the work, including the proportioningbond with old concrete. and mixing of the concrete. Supervision is also of extreme importance to check the reinforcement andWhere high shear resistance is required at the its placing before being joints, shear keys may be-provided.Sprayed curing membranes and release agents should 13.6.1 Before any important operation, such asbe thoroughly removed from joint surfaces. concreting or stripping of the formwork is started, adequate notice shall be given to the construction13.5 Curing supervisor.Curing is the process of preventing the loss of moisture 14 CONCRETING UNDER SPECIALfrom the concrete whilst maintaining a satisfactory CONDITIONStemperature regime. The prevention of moisture lossfrom the concrete is particularly important if the-water- 14.1 Work in Extreme Weather Conditionscement ratio is low, if the cement has a high rate of During hot or cold weather, the concreting should bestrength development, if the concrete contains done as per the procedure set out in IS 7861granulated blast furnace slag or pulverised fuel ash. (Part 1) or IS 7861 (Part 2).The curing regime should also prevent the developmentof high temperature gradients within the concrete. 14.2 Under-Water Concreting The rate of strength development at early ages of 14.2.1 When it is necessary to deposit concrete under. concrete made with supersulphated cement is water, the methods, equipment, materials and significantly reduced at lower temperatures. proportions of the mix to be used shall be submitted to Supersulphated cement concrete is seriously affected and approved by the engineer-in-charge before the by inadequate curing and the surface has to be kept work is started. moist for at least seven days. 14.2.2 Under-water concrete should have a slump135.1 Moist Curing recommended in 7.1. The water-cement ratio shall not Exposed surfaces of concrete shall be kept exceed 0.6 and may need to be smaller, depending on continuously in a damp or wet condition by ponding the grade of concrete or the type of chemical attack. or by covering with a layer of sacking, canvas, hessian For aggregates of 40 mm maximum particle size, the or similar materials and kept constantly wet for at least cement content shall be at least 350 kg/m3 of concrete. seven days from the date of placing concrete in case 14.23 Coffer-dams or forms shall be sufftciently tight 27
  • IS 456 : 2000to ensure still water if practicable, and in any case to surface, and thus avoid formation of laitancereduce the flow of water to less than 3 mAnin through layers. If the charge in the tremie is lost whilethe space into which concrete is to be deposited. depositing, the tremie shall be raised above theCoffer-dams or forms in still water shall be sufficiently concrete surface, and unless sealed by a checktight to prevent loss of mortar through the walls. valve, it shall be re-plugged at the top end, as atDe-watering by pumping shall not be done while the beginning, before refilling for depositingconcrete is being placed or until 24 h thereafter. concrete.14.2.4 Concrete cast under water should not fall freely b) Direct placement with pumps-As in the casethrough the water. Otherwise it may be leached and of the tremie method, the vertical end piece ofbecome segregated. Concrete shall be deposited, the pipe line is always inserted sufficiently deepcontinuously until it is brought to the required height. into the previously cast concrete and should notWhile depositing, the top surface shall be kept as nearly move to the side during pumping.level as possible and the formation of seams avoided. c) Drop bottom bucket -The top of the bucket shallThe methods to be used for depositing concrete under be covered with a canvas flap. The bottom doorswater shall be one of the following: shall open freely downward and outward when a>Tremie-The concrete is placed through vertical tripped. The bucket shall be filled completely and pipes the lower end of which is always inserted lowered slowly to avoid backwash. The bottom sufficiently deep into the concrete which has doors shall not be opened until the bucket rests been placed ~previously but has not set. The on the surface upon which the concrete is to be concrete emerging from the pipe pushes the deposited and when discharged, shall be material that has already been placed to the side withdrawn slowly until well above the concrete. and upwards and thus does not come into direct 4 Bags - Bags of at least 0.028 m3 capacity of contact with water. jute or other coarse cloth shall be filled about When concrete is to be deposited under water two-thirds full of concrete, the spare end turned by means of tremie, the top section of the tremie under so that bag is square ended and securely shall be a hopper large enough to hold one entire tied. They shall be placed carefully in header batch of the mix or the entire contents the and stretcher courses so that the whole mass is. transporting bucket, if any. The tremie pipe shall interlocked. Bags used for this purpose shall be be not less than 200 mm in diameter and shall free from deleterious materials. be large enough to allow a free flow of concrete e>Grouting-A series of round cages made from and strong enough to withstand the external 50 mm mesh of 6 mm steel and extending over pressure of the water in which it~is suspended, the full height to be concreted shall be prepared even if a partial vacuum develops inside the pipe. and laid vertically over the area to~beconcreted Preferably, flanged steel pipe of adequate so that the distance between centres of the cages strength for the job should be used. A separate and also to the faces of the concrete shall not lifting device shall be provided for each tremie exceed one metre. Stone aggregate of not less pipe with its hopper at the upper end. Unless than 50 mm nor more than 200 mm size shall be the lower end of the pipe is equipped with an deposited outside the steel cages over the full approved automatic check valve, the upper end area and height to be concreted with due care to of the pipe shall be plugged with a wadding of prevent displacement of the cages. the gunny’sacking or other approved material A stable 1:2 cement-sand grout with a water- before delivering the concrete to the tremie pipe cement ratio of not less than 0.6 and not more through the hopper, so that when the concrete is than 0.8 shall be prepared in a mechanical mixer forced down from the hopper to the pipe, it will and sent down under pressure (about 0.2 N/mm*) force the plug (and along with it any water in through 38 to 50 mm diameter pipes terminating the pipe) down the pipe and out of the bottom into steel cages, about 50 mm above the bottom ,. end, thus establishing a continuous stream of of the concrete. As the grouting proceeds, the concrete. It will be necessary to raise slowly the pipe shall be raised gradually up to a height of tremie in order to cause a uniform flow of the not more than 6 000 mm above its starting level concrete, but the tremie shall not be emptied so after which it may be withdrawn and placed into that water enters the pipe. At all times after the the next cage for further grouting by the same placing of concrete is started and until all the procedure. concrete is placed, the lower end of the tremie pipe shall be below the top surface of the plastic After grouting the whole area for a height of concrete. This will cause the concrete to build about 600 mm, the same operation shall be up from below instead of flowing out over the repeated, if necessary, for the next layer of 28
  • IS 456 : 2000 600 mm and so on. for testing at 28 days. Additional samples may be The amount of grout to be sent down shall be required for various purposes such as to determine the sufficient to fill all the voids which may be either strength of concrete at 7 days or at the time of striking ascertained or assumed as 55 percent of the the formwork, or to determine the duration of curing, volume to be concreted. or to check the testing error. Additional samples may also be required for testing samples cured by14.2.5 To minimize the formulation of laitance, great accelerated methods as described in IS 9103. Thecare shall be exercised not to disturb the concrete as specimen shall be tested as described in IS 516.far as possible while it is being deposited. 15.4 Test Results of Sample15 SAMPLING AND STRENGTH OFDESIGNED CONCRETE MIX The test results of the sample shall be the average of the strength of three specimens. The individual15.1 General variation should not be more than +15 percent of theSamples from fresh concrete shall be taken as per average. If more, the test results of the sample are invalid.IS 1199 and cubes shall be made, cured and tested at 16 ACCEPTANCE CRITERIA28 days in accordance with IS 516.15.1.1 In order to get a relatively quicker idea of the 16.1 Compressive Strengthquality of concrete, optional tests on beams for The concrete shall be deemed to comply with themodulus of rupture at 72 + 2 h or at 7 days, or strength requirements when both the followingcompressive strength tests at 7 days may be carried condition are met:out in addition to 28 days compressive strength test.For this purpose the values should be arrived at based a) The mean strength determined from any groupon actual testing. In all cases, the 28 days compressive of four consecutive test results compiles withstrength specified in Table 2 shall alone be the criterion the appropriate limits in co1 2 of Table 11.for acceptance or rejection of the concrete. b) Any individual test result complies with the appropriate limits in co1 3 of Table 11.15.2 Frequency of Sampling 16.2 FIexural Strength15.2.1 Sampling Procedure When both the following conditions are met, theA random sampling procedure shall be adopted to concrete complies with the specified flexural strength.ensure that each concrete batch shall have a reasonablechance of being tested that is, the sampling should be 4 The mean strength determined from any groupspread over the entire period of concreting and cover of four consecutive test results exceeds theall mixing units. specified characteristic strength by at least 0.3 N/mm2.15.2.2 Frequency b) The strength determined from any test result isThe minimum frequency of sampling of concrete of not less than the specified characteristic strengtheach grade shall be in accordance with the following: less 0.3 N/mmz. 16.3 Quantity of Concrete Represented byQuantity of Concrete in the Number of Samples Strength Test Results Work, m3 The quantity of concrete represented~by a group of I- 5 1 four consecutive test-results shall include the batches 6- 15 2 from which the first and last samples were taken 16- 30 3 together with all intervening batches. 31-50 4 5 1 and above 4 plus one For the individual test result requirements given in additional sample co1 2 of Table 11 or in item (b) of 16.2, only the for -each additional particular batch from which the sample was taken shall 50 m3 or part thereof be at risk. NOTE-At least one sample shall be taken from each Shift. Where the mean rate of sampling is not specified the Where concrete is produced at continuous production unit, such maximum quantity of concrete that four consecutive as ready-mixed concrete plant, frequency of’sampling may be test results represent shall be limited to 60 m3. agreed upon mutually by suppliers and purchasers. 16.4 If the concrete is deemed not to comply persuant to 16.3, the structural adequacy of the parts affected 15.3 Test Specimen shall be investigated (see 17) and any consequential Three test specimens shall be made for each sample action as needed shall be taken. 29
  • IS 456 : 200016.5 Concrete of each grade shall be assessed e) there is a system to verify that the quality isseparately. satisfactory in individual parts of the structure,16.6 Concrete is liable to be rejected if it is porous especially the critical ones.or honey-combed, its placing has been interrupted 17.2 Immediately after stripping the formwork, allwithout providing a proper construction joint, the concrete shall be carefully inspected and any defectivereinforcement has been displaced beyond the work or small defects either removed or made goodtolerances specified, or construction tolerances have before concrete has thoroughly hardened.not been met. However, the hardened concrete 17.3 Testingmay be accepted after carrying out suitableremedial measures to the satisfaction of the engineer- In case of doubt regarding the grade of concrete used,in-charge. either due to poor workmanship or based on results of cube strength tests, compressive strength tests of17 INSPECTION AND TESTING OF concrete on the basis of 17.4 and/or load test (see 17.6)STRUCTURES may be carried out.17.1 Inspection 17.4 Core TestTo ensure that the construction complies with the 17.4.1 The points from which cores are to be takendesign an inspection procedure should be set up and the number of cores required shall be at thecovering materials, records, workmanship and discretion of the engineer-in-charge and .shall beconstruction. representative of the whole of concrete concerned. ,In no case, however, shall fewer thau three cores be17.1.1 Tests should be made on reinforcement and tested.the constituent materials of concrete in accordance withthe relevant standards. Where applicable, use should 17.4.2 Cores shall be prepared and tested as describedbe made of suitable quality assurance schemes. in IS 516.17.1,.2 Care should be taken to see that: 17.4.3 Concrete in the member represented by a core test shall be considered acceptable if the average 4 design and detail are capable of being executed equivalent cube strength of thecores is equal to at least to a suitable standard, with due allowance for 85 percent of the cube strength of the grade of concrete dimensional tolerances; specified for the corresponding age and no individual b) there are clear instructions on inspection core has a strength less than 75 percent. standards; 17.5 In case the core test results do not satisfy the c) there are clear instiuctions on permissible requirements of 17.4.3 or where such tests have not deviations; been done, load test (17.6) may be resorted to. 4 elements critical to workmanship, structural performance, durability and appearance are 17.6 Loa+ Tests for Flexural Member identified; and 17.6.1 Load tests should be carried out as soon as Table 11 Characteristic Compressive Strength Compliance Requirement (Clauses 16.1 Md 16.3) specified Mean of the Group of Individual ‘kst Grade 4 Non-Overlapping Results In Nlmrn’ Consecutive Test Results In N/mm’ (1) (2) (3)M 15 2 fa + 0.825 X established 2 f,-" N/mm* stundurd deviation(rounded off to neatest 0.5 N/mm*) f, + 3 N/I&, whicheveris greater M 20 2 fe + 0.825 x estublished 2 f,” Nlmm’ Or standarddeviation(rounded above off to nearest0.5 N/mm*) f”’ + 4 N/mm*,whichever iFg*ter NOTE-In the ubsence of establishedv&e of standurd deviution,the vulues given in Table8 may be assumed, attemptshould be and made to obtain results of 30 samples us early us possible to estublishthe vulue of stundurddeviation. 30
  • IS 456 : 2000possible after expiry of 28 days from the time of placing not apply.of concrete. 17.7 Members Other Than Flexural Members17.6.2 The structure should be subjected to a load equalto full dead load of the structure plus 1.25 times the Members other than flexural members should beimposed load for a period of 24 h and then the imposed preferably investigated by analysis.load shall be removed. 17.8 anon-destructive Tests NOTE-Dead load includes self weight of the structural Non-destructive tests are used to obtain estimation of members plus weight of finishes and walls or partitions, if -any, the properties of concrete in the structure. The methods as considered in the design. adopted include ultrasonic pulse velocity [see IS 133 11 (Part l)] and rebound hammer [IS 13311 (Part 2)],17.6.3 The deflection due to imposed load only shallbe recorded. If within 24 h of removal of the imposed probe penetration, pullout and maturity. Non-loa< the structure does not recover at least 75 percent destructive tests provide alternatives to core tests forof the deflection under superimposed load, the test may estimating the strength of concrete in a structure, orbe repeated after a lapse of 72 h. If the recovery is less can supplement the data obtained from a limitedthan 80 percent, the structure shall be deemed to be number of cores. These methods are based on measuring a concrete property that bears someunacceptable. relationship to strength. The accuracy of these methods, If the maximum deflection in mm, shown in part, is determined by the degree of correlationduring 24 h under load is less than 4012/D, where 1 is between strength and the physical quality measuredthe effective span in m; and D, the overall depth of the by the non-destructive tests.section in~mm, it is not necessary for the recovery to Any of these methods may be adopted, in which case thebe measured and the recovery provisions of 17.6.3 shall acceptance criteria shall be agreed upon prior to testing. 31
  • IS 456 : 2000 SECTION 3 GENERAL DESIGN CONSIDERATION18 BASES FOR DESIGN be taken from Table 18 for the limit state of collapse.18.1 Aim of DesignThe aim of design is the achievement of an acceptable 18.3 Durability, Workmanship and Materialsprobability that structures being designed will perform It is assumed that the quality of concrete, steel andsatisfactorily during their intended life. With an other materials and of the workmanship, as verifiedappropriate degree of safety, they should sustain all by inspections, is adequate for safety, serviceabilitythe loads and deformations of normal construction and and durability.use and have adequate durability and adequateresistance to the effects of misuse and fire. 18.4 Design Process Design, including design for durability, construction18.2 Methods of Design and use in service should be considered as a whole.18.2.1 Structure and structural elements shall normally The realization of design objectives requiresbe designed by Limit State Method. Account should compliance with clearly defined standards forbe taken of accepted theories, experiment and materials, production, workmanship and alsoexperience and the need to design for durability. maintenance and use of structure in service.Calculations alone do not produce safe, serviceable anddurable structures. Suitable materials, quality control, 19 LOADS AND FORCESadequate detailing and good supervision are equally 19.1 Generalimportant. In structural design, account shall be taken of the dead,18.2.2 Where the Limit State Method can not be imposed and wind loads and forces such as thoseconveniently adopted, Working Stress Method (see caused by earthquake, and effects due to shrinkage,Annex B) may be used. creep, temperature, em, where applicable. 18.2.3 Design Based on Experimental Basis 19.2 Dead LoadsDesigns based on experimental investigations on Dead loads shall be calculated on the basis of unitmodels or full size structure or element may be weights which shall be established taking intoaccepted if they satisfy the primary requirements consideration the materials specified for construction.of 18.1 and subject to experimental details and theanalysis connected therewith being approved by the 19.2.1 Alternatively, the dead loads may be calculatedengineer-in-charge. on the basis of unit weights of materials given in IS 875 (Part 1). Unless more accurate calculations are Where the design is based on experimental warranted, the unit weights of plain concrete and investigation on full size structure or element, load tests reinforced concrete made with sand and gravel or shall be carried out to ensure the following: crushed natural stone aggregate may be taken as a) The structure shall satisfy the requirements for 24 kN/m” and 25 kN/m” respectively. deflection (see 23.2) and cracking (see 35.3.2) when subjected to a load for 24 h equal to the 19.3 Imposed Loads, Wind Loads and Snow Loads characteristic load multiplied by 1.33 y,, where Imposed loads, wind loads and snow loads shall be y, shall be taken from Table 18, for the limit state assumed in accordance with IS 875 (Part 2), IS 875 of serviceability. If within 24 h of the removal (Part 3) and IS 875 (Part 4) respectively. of the load, the structure does not show a recovery of at least 75 percent of the maximum 19.4 Earthquake Forces deflection shown during the 24 h under,the load, The earthquake forces shall be calculated in the test loading should be repeated after a lapse accordance with IS 1893. of 72 h. The recovery after the second test should be at least 75 percent of the maximum deflection 19.5 Shrinkage, Creep and Temperature Effects shown during the second test. If the effects of shrinkage, creep and temperature are NOTE-If the maximum deflection in mm, shown during 24 h underload is less than 40 P/D where 1is the effective span liable to affect materially the safety and serviceability in m; and D is the overall depth of-the section in mm, it is not of the structure, these shall be taken into account in necessary for the recovery to be measured. the calculations (see 6.2.4, 6.2.5 and 6.2.6) and IS 875 (Part 5). b) The structure shall have adequate strength to sustain for 24 h, a total load equal to the charac- 19.5.1 In ordinary buildings, such as low rise dwellings teristic load multiplied by 1.33 y, where y, shall whose lateral dimension do not exceed 45 m, the 32
  • P IS456:2800effects due to temperature fluctuations and shrinkage 28.2 Slidingand creep can be ignored in &sign calculations. The strucn~eshall have a factor against sliding of not less than 1.4 under the most adverse combination of the19.6 Other Forces and Effects applied charact&stic forces. In this case only 0.9 timesIn addition, account shall ‘be taken of the following the characteristic dead load shall be taken into account.forces and effects if they are liable to affect materially 28.3 Probable Variation in Dead Loadthe safety and serviceability of the structure: To ensure stability at all times, account shall be taken 4 Foundation movement (see IS 1904), of probable variations in dead load during construction, b) Elastic axial shortening, repair or other temporary measures. Wind and seismic loading shall be treated as imposed loading. cl Soil and fluid pressures [see IS 875 (Part S)], 28.4 Moment Connection 4 Vibration, In designing the framework of a building provisions 4 Fatigue, shall be made-by adequate moment connections or by 9 Impact [see IS 875 (Part 5)], a system of bracings to effectively transmit all the g) Erection loads [see IS 875 (Part 2)], and horizontal forces to the foundations. h) Stress concentration effect due to point load and 20.5 Lateral Sway the like. Under transient wind load the lateral sway at the top19.7 Combination of Loads should not exceed H/500, where H is the total height of the building. For seismic.loading, reference shouldThe combination of loads shall be as given in IS 875 be made to IS 1893.(Part 5). 21 F’IRBRBSISTANCR19.8 Dead Load Counteracting Other L,oads and 21.1 A structure or structural element required to haveForces fire resistance should be designed to possess anWhen dead load counteracts the effects due to other appropriate degree of resistance to flame penetration;loads and forces in structural member or joint, special heat transmission and failure. The fire resistance of acare shall be exercised by the designer to ensure structural element is expressed in terms of time in hoursadequate safety for possible stress reversal. in accordance with IS 1641. Fire resistance of concrete elements depends upondetails of member size, cover19.9 Design Load to steel reinforcement detailing and type of aggregateDesign load is the load to be taken for use in the (normal weight or light weight) used in concrete.appropriate method of design; it is the characteristic General requirements for fue protection are given inload in case of working stress method and characteristic IS 1642.load with appropriate partial safety factors for limit 21.2 Minimum requirements of concrete cover andstate design. member dimensions for normal-weight aggregate20 STABILITY OF THE STRUCTURE concrete members so as to have the required fire resistance shall be in accordance with 26.4.3 and20.1 Overturning Fig. 1 respectively.The stability of a structure as a whole against 21.3 The reinforcement detailing should reflect theoverturning shall be ensured so that the restoring changing pattern of the structural section and ensuremoment shall be not less than the sum of 1.2 times the that both individual elements and the structure as amaximum overturning moment due to the charac&stic whole contain adequate support, ties, bonds anddead load and 1.4 times the maximum overturning anchorages for the required fire resistance.moment due to the characteristic imposed loads. Incases where dead load provides the restoring moment, 21.3.1 Additional measures such as application of tireonly 0.9 times the characteristic dead load shall be resistant finishes, provision of fire resistant falseconsidered. Restoring moment ilue to imposed loads ceilings and sacrificial steel in tensile zone, should beshall be ignored. adopted in case the nominal cover required exceeds 40 mm for beams and 35 mm for slabs, to give 20.1.1 The anchorages or counterweights provided protection against~spalling. for overhanging members (during construction and service) should be such that static equilibrium 21.4 Specialist literature may be referred to for should remain, even when overturning moment is determining fire resistance of the structures which have doubled. not been covered in Fig. 1 or Table 16A. 33
  • IS 456 : 2000 b) Continuous Beam or Slab - In the case of 22.4.1 Arrungement of Imposed Load continuous beam or slab, if the width of the 4 Consideration may be limited to combinations support is less than l/12 of the clear span, the Of: effective span shall be as in 22.2 (a). If the supports are wider than I/12 of the clear span 1) Design dead load on all spans with full or 600 mm whichever is less, the effective span design imposed load on two adjacent spans; shall be taken as under: and 1) For end span with one end fixed and the 2) Design dead load on all spans with full design imposed load on alternate spans. other continuous or for intermediate spans, the effective span shall Abethe clear span b) When design imposed load does not exceed between supports; three-fourths of the design dead load, the load arrangement may be design dead load and design 2) For end span with one end free and the other imposed load on all the spans. continuous, the effective span shall be equal to the clear span plus half the effective depth NOTE - For beams and slabs continuous over support 22.4.1(a) may be assumed. of the beam or slab or the clear span plus half the width of the discontinuous support, 224.2 Substitute Frame whichever is less; For determining the moments and shears at any floor 3) In the case of spans with roller or rocket or roof level due to gravity loads, the beams at that bearings, the effective span shall always be level together with columns above and below with their the distance between the centres of bearings. far ends fixed may be considered to constitute the frame. cl Cantilever-The effective length of a cantilever shall betaken as its length to the face of the Where side sway consideration becomes support plus half the effective depth except critical due to unsymmetry in geometry or loading, where it forms the end of a continuous beam rigorous analysis may be required. where the length to the centre of support shall 224.3 For lateral loads, simplified methods ~may be be taken. used to obtain the moments and shears for structures 4 Frames-In the analysis of a continuous frame, that are symmetrical. For unsymmetrical or very tall centre to centre distance shall be used. structures, more rigorous methods should be used. 22.5 Moment and Shear Coeffkients for22.3 Stiffness Continuous Beams22.3.1 Relative Stlfhess 22.5.1 Unless more exact estimates are made, forThe relative stiffness of the members may be based on beams of uniform cross-section which supportthe moment of inertia of the section determined on substantially uniformly distributedloads over three orthe basis of any one of the following definitions:. more spans which do not differ by more than 15 percent of the longest, the bending moments and shear forces a) Gross section - The cross-section of. the used in design may be obtained using the coefficients member ignoring reinforcement; given in Table 12 and Table 13 respectively. b) Transformed section - The concrete cross- For moments at supports where two unequal spans section plus the area of reinforcement meet or in case where the spans are not equally loaded, transformed on the basis of modular ratio (see the average of the two values for the negative moment B-1.3); or at the support may be taken for design. c) Cracked section - The area of concrete in Where coefficients given in Table 12 are used for compression plus the area of reinforcement calculation of bending moments, redistribution referred transformed on the basis of modular ratio. to in 22.7 shall not be permitted.The assumptions made shall be consistent for all the 22.5.2 Beams and Slabs Over Free End Supportsmembers of the structure throughout any analysis. Where a member is built into a masonry wall which22.3.2 For deflection calculations, appropriate values develops only partial restraint, the member shall beof moment of inertia as specified in Annex C should designed to resist a negative moment at the face of thebe used. support of WU24 where W is the total design load and I is the effective span, or such other restraining22.4 Structural Frames moment as may be shown to be applicable. For such aThe simplifying assumptions as given in 22.41 condition shear coefficient given in Table 13 at theto 22.4.3 may be used in the analysis of frames. end support may be increased by 0.05. 35
  • IS 456 : 2000 Table 12 Bending Moment Coeffkients (Cluu&?22.5.1)-QPeof Load Span Moments Support Moments * 4 c Near Middle At Middle At Support At Other of EndSpnn of Interior Nextto the Interior SPon EndSupport SUPports (1) (2) (3) (4) (5)Deadloadandimposed 1 1 .I 1 load (fixed) +i? +iz -?Ti -12 Imposed load (not 1 1 ‘lo -- I -- 1 fiXed) +12 9 9 NOTE -For obtaining the bending moment, the coefficient shall be multiplied by the total design load and effective span. Table 13 Shear for Coeffkients (Clauses 22.5.1 and 22.52) TypeofLmd At End At Support Next to the At All Other SUPport End Support Interior supports c 4 Outer Side Inner Side (1) (2) (3) (4) (5)Dead load and imposed 0.4 0.6 0.55 0.5 load (fixed)Imposed load (not 0.45 0.6 0.6 0.6 fixed) NOTE -For obtaining the shear force, the coeftkient shall be multiplied by the total design load.22,6 Critical Sections for Moment and Shear 23 BEAMS22.6.1 For monolithic construction, the moments 23.0 Effective Depthcomputed a% the~face of the supports shall be used in Effective depth of a beam is the distance between thethe design of the members at those sections. For non- centroid of the area of tension reinforcement and themonolithic construction the design of the membershall maximum compression fibre, excluding the thicknessbe done keeping in view 22.2. of finishing material not placed monolithically with 22.6.2 Critical Section for Shear the member and the thickness of any concrete provided to allow for wear. This will not apply to deep beams. The shears computed at the face of the support shall be used in the design of the member at that section 23.1 T-Beams and L-Beams except as in 23.1.1 Gene& When the reaction in the direction of the A slab which is assumed to act as a compression applied shear introduces compression into the end flange of a T-beam or L-beam shall satisfy the region of the member, sections located at a distance following: less than d from the face of the support may be designed for the same shear as that computed at a) The slab shall be cast integrally with the web, distance d (see Fig. 2). or the web and the slab shall be effectively bonded together in any other manner; and NOTE-The abwe clausesare applicable for beamsgeneral!y car@ing uniformly distributedload or where the principal load b) If the main reinforcement of the slab is parallel is located farther thzut fromthe face ofthc support. 2d to the beam, transverse reinforcement shall be provided as in Fig. 3; such reinforcement shall 22.7 Redistribution of Moments not be less than 60 percent of the main Redistribution of moments may be done in accordance reinforcement at mid span of the slab. with 37.1.1 for limit state method and in accordance 23.1.2 Effective Width of Flange with B-l.2 for working stress method. However, where simplified analysis using coefficients is adopted, In the absence of more accurate determination, the redistribution of moments shall not be done. effective width of flange may be taken as the following 36
  • IS456:2WO I I ‘r J; f ‘c I Ld_ d (b) ! I’ llllll1 I (cl FIG. 2 TYPICALSumxc CONDITIONS LOCA~G FACI~RED FOR SHEAR FORCEbut in no case greater than the breadth of the web plus structure or finishes or partitions. The deflection shallhalf the sum of the clear distances to the adjacent beams generally be limited to the following:on either side. a) The final deflection due to all loads including b the effects of temperature, creep and shrinkage a) For T-beams, b, =-z+bW + 6Df and measured from the as-cast level of the , supports of floors, roofs and all other horizontal b b) For L-beams, b, =12+bw+3Df members, should not normally exceed span/250. b) The deflection including the effects of c) For isolated beams, the effective flange width temperahue, creep and shrinkage occurring after shahbe obtained as below but in no case greater erection of partitions and the application of than the actual width: finishes should not normally exceed span/350 or 20 mm whichever is less. T-beam,b,=++b, 23.2.1 The vertical deflection limits may generally be ” +4 0b assumed to be satisfied provided that the span to depth ratios are not greater than the values obtained as below: L-beam,b,=++b, a) Basic values of~span to effective depth ratios for spans up to 10 m: Cantilever 7where Simply supported 20 b, = effective width of flange, Continuous 26 I, = distance between points of zero moments b) For spans above 10 m, the values in (a) may be in the beam, multiplied by lo/span in metres, except for cantilever in which case deflection calculations bw = breadth of the web, should be made. D, = thickness of flange, and c) Depending on the area and the stress of b = actual width of the flange. steel for tension reinforcement, the values in (a) NOTE - For continuous beams nndframes. ‘I,,’ may be or(b) shall be modified by multiplying with the assumedus 0.7times the effective span. modification factor obtained as per Fii. 4. 4 Depending on the’ area of compression23.2 Control of Deflection reinforcement, the value of span to depth ratioThe deflection of a structure or part thereof shall not be further modified by multiplying with theadversely affect the appearance or efficiency of the modification factor obtained as per Fig. 5. 37
  • IS 456 : 2ooo *. L I I ----_ I- --- A --a - t m-e- SECTION XX FIG. 3 TRANSVERSE RJYNWRCEMENT INFLANGE T-BFAM OF WHEN MAINREDUOR~EWENT OF SLABISPARALLELTOTHEBJZAM e) For flanged beams, the values of (a) or (b) be on area of section equal to b, d, modified as per Fig. 6 and the reinforcement NOTE-When ddlcctiona arc requind to be calculated.the percentage for use in Fig. 4 and 5 should be based m&odgiveninAnnexCtnaybcwfd. 0 04 04 1.2 l-6 2-O .24 2-B 30 PERCENTAGE TENSION REINFORCEMENT Amlofcross-scctionofsteelrcquired f,=O.SE f ’ Annofcross-@on of steelprovided FIG.4 MODIFICATTON FA~I-~R TENSION FQR RHNF~RCEMENT 38
  • 0 040 la00 140 2.00 2-50 MC PERCENTAOE COMPRESSION REINFORCEMENT FIG.5 MODIFICATION FACTOR COMPRESSION FOR REINFORCEMEW RATIO OF WEB WIDTH to FLANOE WIDTH FIG. 6 REDUCIION FACKIRS RATIOS SPAN EFPEC~~VB FOR OP TO DFPIM FLANOED FOR BUMS23.3 Slenderness Limits for Beams to9hsure NOTESLateral Stability 1 FocsIQkp~panningilrhvodircctions.the shortcrofthehvo spansshpuld be used for calculating the span to effectiveA simply supported or continuous beam shall be so depth ratios.proportioned that the clear distance between thelateral 2 For two-way slabs of shoti spans (up to 3.5 m) with mild steel rcinfonxmcnt, the span to overall depth ratios given 250 b2 below may generally be assumed to satisfy verticalrestraints does not exceed 60 b or - whichever deflection limits for loading class up to 3 kN/m’. dis less, where d is the effective depth of the beam and Simply supportedslabs 35b thebreadth of the compression face midway between Continuousslabs 40the lateral restraints. For high stmngthdeformedbarsof gradeFe 415. the values given above should be multiplied by 0.8.For a cantilever, the clear distance from the free endof the cantilever to the lateral restraint shall not 24.2 Slabs Continuous Over Supportsexceed 25 b or w whichever is less. Slabs spanning in one direction and continuous over d supports shall be designed according to the provisions aDDkabk to continuous beams.24 SOLID SLABS 24.3 Slabs Monolithic with Suuuorts __24.1 General Bending moments in slabs (except flat slabs)constructedThe provisions of 23.2 for beams apply to slabs monolithically with the supports shall be calculated byalso. taking such slabs either as continuous over supports and 39
  • IS 456 : 2000capable of free rotation, or as members of a continuous c) For two or more loads not in a line in theframework with the supports, taking into account the direction of the span, if the effective width ofstiffness of such supports. If such supports are formed slab for one load does not overlap the effectivedue to beams which justify fixity at the support of slabs, width of slab for another load, both calculatedthen the effects on the supporting beam, such as, the as in (a) above, then the slab for each load canbending of the web in the transverse direction of the be designed separately. If the effective widthbeam and the torsion in thelongitudinal direction of the of slab for one load overlaps the effective widthbeam, wherever applicable, shall also be considered in of slab for an adjacent-load, the overlappingthe design of the beam. portion of the slab shall be designed for the combined effect of the two loads.24.3.1 For the purpose of calculation of moments inslabs in a monolithic structure, it will generally be mble 14 Valws ofk for Siiply Supported antIsufficiently accurate to assume that members connected continuous slatt6to the ends of such slabs are fixed in position and (C&W X3.2.1)direction at the ends remote from their connectionswith the slabs. Old &-forSimply Afor conttnuoua supportedslaba SlPbS24.3.2 Slabs Carrying Concentrated Load 0.1 0.4 0.4 0.2 0.8 0.824.3.2.1 If a solid slab supported on two opposite edges, 0.3 1.16 1.16carries concentrated loads the maximum bending 0.4 1.48 1.44 0.5 1.72 1.68moment caused by the concentrated loads shall be 0.6 l.% 1.84assumed to be resisted by an effective width of slab 0.7 2.12 1.96(measured parallel to the supporting edges) as follows: 0.8 2.24 2.08 0.9 2.36 2.16 a) For a single concentrated load, the effective 1.Oand above 2.48 2.24 width shall be calculated in accordance with the following equation provided that it shall not d) For cantilever solid slabs, the effective width exceed the actual width of the slab: shall be calculated in accordance with the following equation: bef=~ b,= 1.2 a1 + a where re b ef = effective width, b al = effective width of slab, 9 = distanceof the concentrated load from the face of the cantilever support, and k = constant having the values given in Table a = widthof contact area of the concentrated 14 depending upon the ratio of the width load measured parallel to the supporting of the slab (r-) to the effective span fcl, edge. X = distance of the centroid of the Provided that the effective width of the cantilever concentrated load from nearer support, slab shall not exceed one-third the length of the 1 ef = effective span, and cantilever slab measured parallel to the fixed edge. a = width of the contact area of the And provided further that when the concentrated concentrated load from nearer support load is placed near the extreme ends of the length measured parallel to the supported edge. of cantilever slab in the direction parallel to the fixed edge, the effective width shall not exceed And provided further that in case of a load near the above value, nor shall it exceed -half the the unsupported edge of a slab, the effective above value plus the distance of the concentrated width shall not exceed the above value nor half load from the extreme end measured in the the above value plus the distance of the load from direction parallel to the fixed edge. the unsupported edge. For slabs other than solid slabs, the effective b) For two or more concentrated loads placed in a width shall depend on the ratio of the transverse and line in the direction of the span, the bending longitudinal flexural rigidities~of the slab. Where this moment per metre width of slab shall be ratio is one, that is, where the transverse and calculated separately for each load according to longitudinal flexural rigidities are approximately its appropriate effective width of slab calculated equal, the value of effective width as found for solid as in (a) above and added together for design slabs may be used. But as the ratio decreases, calculations. proportionately smaller value shall be taken. 40
  • I$456 : 200024.3.2.3 Any other recognized method of analysis for signs), the total should be equal to that from (a).cases of slabs covered by and and If the resulting support moments are signifi-for all other cases of slabs may be used with the cantly greater than the value from Table 26, theapproval of the engineer-in-charge. tension steel over the supports will need to be24.3.2.4 The critical section for checking shear shall extended further. The procedure should be asbe as given in follows: 1) Take the span moment as parabolic between24.4 Slabs Spanning in ‘ho Directions at Right supports: its maximum value is as foundAngles from (d).The slabs spanning in two directions at right angles 2) Determine the points of contraflexure of theand carrying uniformly distributed load may be new support moments [from (c)] with thedesigned by any acceptable theory or by using span moment [from (l)]. coefficients given in Annex D. For determining Extend half the support tension steel at each 3)-bending moments in slabs spanning in two directions end to at least an effective depth or 12 bar at right angles and carrying concentrated load, any diameters beyond the nearest point of accepted method approved by the engineer-in-charge contraflexure. may be adopted. 4) Extend the full area of the support tension NOTE-The most commonly used elastic methods an based steel at each end to half the distance from on Pigeaud’s or Wester-guard’s theory and the most commonly used limit state of collupse methodis based on Johansen’syield- (3). line theory. 24.5 Loads on supporting Beams24.4.~ Restrained Slab with Unequal Conditions at The loads on beams supporting solid slabs spanningAdjacent Panels in two directions at right angles and supporting uniformly distributed loads, may be assumed to be inIn some cases the support moments calculated from accordance with Fig. 7.Table 26 for adjacent panels may differ significantly.The following procedure may be adopted to adjust 25 COMPRESSION MEMBERSthem: 25.1 Defdtions a) Calculate the sum of moments at midspan and 25.1.1 Column or strut is a compression member, the supports (neglecting signs). effective length of which exceeds three times the least b) Treat the values from Table 26 as fixed end lateral dimension. moments. 25.1.2 Short and Slender Compression Members cl According to the relative stiffness of adjacent spans, distribute the fixed end moments across A compression member may be considered as short the supports, giving new support moments. 1 1 when both the slenderness ratios Cx and x are less d) Adjust midspan moment such that, when added D b to the support moments from (c) (neglecting than 12: L LOAD -0 IN THIS SHADED AREA To BE CARRIED &Y BEAM ‘6’ -LOAD IN THIS SHADED AREA TO BE CARRIED By BEAM ‘A’ FIG.7 LoADCAxnranBY !bPPGKl7NGBEAMS 41
  • IS 456 : 2000where where I,, = effective length in respect of the major b = width.of that cross-section, and axis, D= depth in respect of the major axis, D= depth of the cross-section measured in the 1 = effective length in respect of the minor plane under consideration. eY axis, and 25.4 Minimum Eccentricity b = width of the member. All columns shall Abe designed for minimumIt shall otherwise be considered as a slender eccentricity, equal to the unsupported length of column/compression member. 500 plus lateral dimensions/30, subject to a minimum25.1.3 Unsupported Length of 20 mm. Where bi-axial bending is considered, it is sufficient to ensure that eccentricity exceeds theThe unsupported length, 1, of a compression member minimum about one axis at a time.shall be taken as the clear distance between endrestraints except that: 26 REQUIREMENTS GOVERNING 4 in flat slab construction, it shall be cleardistance REINFORCEMENT AND DETAILING between the floor and the lower extremity of the capital, the drop panel or slab whichever is 26.1 General the least. Reinforcing steel of same type and grade shall be used b) in beam and slab construction, it shall be the as main reinforcement in a structural member. clear distance between the floor and the However, simultaneous use of two different types or underside of the shallower beam framing into grades of steel for main and secondary reinforcement the columns in each direction at the next higher respectively is permissible. floor level. 26.1.1 Bars may be arranged singly, or in pairs in c>in columns restrained laterally by struts, it shall contact, or in groups of three or four bars bundled in be the clear distance between consecutive contact. Bundled bars shall be enclosed within stirrups struts in each vertical plane, provided that to be or ties. Bundled bars shall be tied together to ensure an adequate support, two such struts shall the bars remaining together. Bars larger than 32 mm meet the columns at approximately the same diameter shall not be bundled, except in columns. level and the angle between vertical planes 26.1.2 The recommendations for detailing for through the struts shall not vary more than 30” earthquake-resistant construction given in IS 13920 from a right angle. Such struts shall be of should be taken into consideration, where applicable adequate dimensions and shall have sufficient (see afso IS 4326). anchorage to restrain the member against lateral deflection. 26.2 DCvelopment of Stress in Reinforcement d) in columns restrained laterally by struts or The calculated tension or compression in any bar at beams, with brackets used at the junction, it shall any section shall be devel-oped on peach side -of the be the clear distance between the floor and the section by an appropriate development length or end lower edge of the bracket, provided that the anchorage or by a combination thereof. bracket width equals that of the beam strut and 26.2.1 Development Length of Bars is at least half that of the column. The development length Ld is given by25.2 Effective Length of Compression MembersIn the absence of more exact analysis, the effective Ld ALlength 1, of columns may be obtained as described in 4%Annex E. where 25.3 Slenderness Limits for Columns d = nominal diameter of the bar, 25.3.1 The unsupported length between end restraints b, = stress in bar at the section considered at design shall not exceed 60 times the least lateral dimension load, and of a column. t = design bond stress given in 25.3.2 If, in any given plane, one end of a column is NOTES unrestrained, its unsupported length, 1,shall not exceed 1 ‘lie development lengthincludesmchorngevalues of hooks in tension reinforcement. lOOb* -. 2 For bars of sections other than circular,the. development D let@ should be sufficient to develop the stress in the bru by bond. 42
  • I!3456:200026.2.1.1 Design bond stress in limit state method for plain bars in tension shall be as below:Grade of concrete -M 20 M 25 M 30 M 35 M40 andaboveDesign bond stress, 1.2 1.4 1.5 1.7 1.9zhd,N/mm2For deformed bars conforming to IS 1786 these values 2) In the compression zone, from the mid depthshall be increased by 60 percent. ofthe beam.For bars in compression, the values of bond stress for b) Stirrups-Notwithstanding any of thebars in tension shall be increased-by 25 percent. provisions of this standard, in case of secondaryThe values of bond stress in working stress design, reinforcement, such as stirrups and transverseare given in B-2.1. ties, complete development lengths and anchorage shall be deemed to have been26.2.1.2 Bars bundled in contact provided when the bar is bent through an angleThe development length of each bar of bundled bars of at least 90” round a bar of at least its ownshall be that for the individual bar, increased by 10 diameter and is continued beyond the end of thepercent for~two bars in contact, 20 percent for three curve for a length of at least eight diameters, orbars in contact and 33 percent for four bars in contact. when the bar is bent through an angle of 135” and is continued beyond the end of the curve26.2.2 Anchoring Reinforcing Bars for a length of at least six bardiametersor when26.2.2.1 Anchoring bars in tension the bar is bent through an angle of 180” and is a) Deformed bars may be used without end continued beyond the end of the curve for a anchorages provided development length length of at least four bar diameters. requirement is satisfied. Hooks should normally Bearing stresses at be&s be provided for plain bars in tension. lb) Bends and hooks - Bends and hooks shall The bearing stress in concrete for bends and hooks conform to IS 2502 describedin IS 2502 need not be checked. The bearing stressinside a bend in tiy otherbend shall be calculated 1) Bends-The anchorage value of bend shall as given below: be taken as 4 times the diameter of the bar for each 45” bend subject to a maximum of Bearing stress = !L 16 times~the diameter of the bar. 4 2) Hooks-The anchorage value of a standard where U-type hook shall be equal to 16 times the diameter of the bar. FM = tensile force due to design loads in a bar or group of bars, Anchoring bars in compression r = internal radius of the bend, andThe anchorage length of straight bar in compression Q = size of the baror, in bundle, the size of barshall be equal to the development length of bars in of equivalent area.compression as specified in 26.2.1. The projected For limit state method of design, this stress shall notlength of hooks, bends and straight lengths beyondbends if provided for a bar in compression, shall only exceed - 1.5f,, where fd is the characteristic cubebe considered for development length. 1+2$/a strength of concrete and a, for a particularbaror group26.2.2.3 Mechanical devices for anchorage of bars in contact shall be taken as the centre to centreAny mechanical or other device capable of developing distance between barsor groups of bars perpendicularthe strength of the bar without damage to concrete may to the plane of the bend; for a bar or group ofbe used as anchorage withthe approval of the engineer- bars adjacent to the face of the member a shall bein-charge. taken as the cover plus size of bar ( 6). For working26.2.2.4 Anchoring shear reinforcement *stress method of design, the bearing stress shall a) Inclined bars - The development length shall not exceed A. f be as for bars in tension; this length shall be 1+2@/a measured as under: If a change in direction of tension or 1) In tension zone, from the end of the sloping compression reinforcement induces a resultant force or inclined portion of the bar, and acting outwardtending to split the concrete, such force 43
  • IS 456 : 2000should be taken up by additional links or stirrups. Bent 4tension bar at a re-entrant angle should be avoided. -+Lo V26.2.3 Curtailment of Tension Reinforcement in whereFlexural Members M, = moment of resistance of the section26.2.3.1 For curtailment, reinforcement shall extend assuming all reinforcement at the sectionbeyond the point at which it is no longer required to to be stressed to fd;resist flexure for a distance equal to the effective depth 0.87 f, in the case of limit state design fJ =of the member or 12 times the bar diameter, whichever and the permissible stress on in the caseis greater except at simple support or end of cantilever. of working stress design;In addition 26,2.3.2 to shall also be satisfied. v= shear force at the section due to design NOTE-A point ut which reinforcement is no longer required to resist flexure is where the resistance moment of the section, loads; considering only the continuing burs. is equal to the design L, = sum of the anchorage beyond the centre moment. of the support and the equivalent26.2.3.2 Flexural reinforcement shall not be terminated anchorage value of any hook orin a tension zone unless any one of the following mechanical anchorage at simple support;conditions is satisfied: and at a point of inflection, L,, is limited to the effective depth of the members or 4 The shear at the cut-off point does not exceed 124t,whichever is greater; and two-thirds that permitted, including the shear strength of web reinforcement provided. # = diameter of bar. The value of M, /V in the above expression may be b) Stirrup area in excess of that required for shear increased by 30 percent when the ends of the and torsion is provided along each terminated reinforcement are confined by a compressive reaction. bar over a distance from the cut-off point equal to three-fourths the effective depth of the Negative moment reinforcement member. The excess stirrup area shall be not At least one-third of the total reinforcement provided less than 0.4 bs/fy’ where b is the breadth of for negative moment at the support shall extend beyond beam, s is the spacing andfy is the characteristic the point of inflection for a distance not less than the strength of reinforcement in N/mm*. The effective depth of the member of 129 or one-sixteenth resulting spacing shall not exceed d/8 j$,where of the clear span whichever is greater. p, is the ratio of the area of bars cut-off to the total area of bars at the section, and d is the Curtailment of bundled bars effective depth. Bars in a bundle shall terminate at different points cl For 36 mm and smaller bars, the continuing bars spaced apart by not less than 40 times the bar diameter provide double the area required for flexure at except for bundles stopping at a support. the cut-off point and the shear does not exceed 26.2.4 Special Members three-fourths that permitted. Adequate end anchorage shall be provided for tension26.2.3.3 Positive moment reinforcement reinforcement in flexural members where reinforce- 4 At least one-third the positive moment ment stress is not directly proportional to moment, reinforcement in simple members and one- such as sloped, stepped, or tapered footings; brackets; fourth the positive moment reinforcement in deep beams; and members in which the tension continuous members shall extend along the same reinforcement is not parallel to the compression face, face of the member into the support, to a length 26.2.5 Reinforcement Splicing equal to L,/3. Where splices are provided in the-reinforcing bars, they , b) When a flexural member is part of the primary shall as far as possible be away from the sections of lateral load resisting system, the positive reinforcement required to be extended into the maximum stress and be staggered. It is recommended support as described in (a) shall be anchored to that splices in flexural members should not be at sections where the bending moment is more than 50 develop its design stress in tension at the face percent of the moment of resistance; and not more than of the support. half the bars shall be spliced at a section. cl At simple supports and at points of inflection, Where more than one-half of the bars are spliced at a positive moment tension reinforcement shall be section or where splices are made at points of limited to a diameter such that Ld computed for maximum stress, special precautions shall be taken, f, by 26.2.1 does not exceed
  • lS456:2MlOsuch as increasing the length of lap and/or using spirals at a time; such individual splices within a bundleor closely-spaced stirrups around the length of the shall be staggered.splice. 26.252 #retigth of w&k26.2.5.1 Lap splices The following values may be used where the strength a) Lap splices shall not be used for bars larger than of the weld has been proved by tests to be at least as 36 mm; for larger diameters, bars ~may be great as that of the parent bar. welded (see 12.4); in cases where welding-is a) Splices in compassion - For welded splices not practicable, lapping of bars larger than and mechanical connection, 100 percent of the 36 mm may be permitted, in which case design strength of joined bars. additional spirals should be provided around the b) Splices in tension lapped bars. 1) 80 percent of the &sign strength of welded W Lap splices shall be considered as staggered if bars (100 percent if welding is strictly the centre to centre distance of the splices is supervised and if at any cross-section of the not less than 1.3 times the lap length calculated member not more than 20 percent of the as described in (c). tensile reinforcement is welded). cl Lap length including anchorage value of hooks for bars in flexural tension shall be Ld (see 2) 100 percent of design strength of mecha- nical connection. 26.2.1) or 309 whichever is greater and for direct tension shall be 2L, or 309 End-bearing splices whichever is greater. The straight length of the End-bearing splices shall be used only for bars in lap shall not be less than lS$ or 200 mm. The compression. The ends of the bars shall be square cut following provis’mns shall also apply: and concentric bearing ensured by suitable devices. Where lap occurs for a tension bar located at: 26.3 Spacing of Reinforcement 1) top of a section as cast and theminimum cover is less than twice the diameter of the lapped 26.3.1 For the purpose of this clause, the diameter of bar, the lap length shall be increased by a factor a round bar shall be its nominal diameter, and in the of 1.4. case of bars which are not round or in the case of deformed bars or crimped bars, the diameter shall be 2) comer of a section and the minimum cover to taken as the diameter of a circle giving an equivalent either face is less than twice the diameter of effective area. Where spacing limitations and the lapped bar or where the clear distance minimum concrete cover (see 26.4) are based on bar between adjacent laps is less than 75 mm or 6 diameter, a group of bars bundled in contact shall be times the diameter of lapped bar, whichever is treated as a single bar of diameter derived from the greater, the lap length should be increased by a total equivalent area. factor of 1.4. Where both condition (1) and (2) apply, the lap 26.3.2 Minimum Distance Between Individual Bars length should be increased by a factor of 2.0. The following shall apply for spacing of bars: NOTE-Splices in tension members shall be enclosed in spirals made of bus not less than 6 mm diameter with pitch a) The horizontal distance between two parallel not more than 100 mm. main reinforcing bars shall usually be not-less than the greatest of the following: 4 The lap length in compression shall be equal to the development length in compression, 1) Thediameterofthebarifthediatneteraare calculated as described in 26.21, but not less equal, than 24 + 2) The diameter of the larger bar if the diameters are unequaI, and e) When bars of two different diameters are to be spliced, the lap length shall be calculated on 3) 5 mm more than the nominal maximum size of coarse aggregate. the basis of diameter of the smaller bar. NOTE4ldsdwrnutprccludethcuscoflaqex heof f) When splicing of welded wire fabric is to be aggregatesbeyond the congested teinforcemt in tb carried out, lap splices of wires shall be made same mcmk, the size of -gates m8y be rsduced so that overlap measured between the extreme aroundcongested reinforcementto comply with thir provi8ioll. cross wires shall be not less than the spacing of cross wires plus 100 mm. W Greater horizontal .&&ance than the minimum la In case of bundled bars, lapped splices of specified in (a) should be provided wherever bundled bars shall be made by splicing one bar possible. However when needle vibrators are 4s
  • IS 456 : 2000 used the horizontal distance between bars of a 26.4 Nominal Cover to Reinforcement group may be reduced to two-thirds the 26.4.1 Nominal Cover nominal maximum size of the coarse aggregate, provided that sufficient space is left between Nominal cover is the design depth of concrete cover groups of bars to enable the vibrator to be to all steel reinforcements, ,including links. It is the immersed. dimension used in design and indicated in the drawings. It shall be not less than the diameter of the bar. cl Where there are two or more rows of bars, the bars shall be vertically in line and the minimum 26.4.2 Nominal Cover to Meet Durability Requirwnent vertical distance between the bars shall be Minimum values for the nominal cover of normal- 15 mm, two-thirds the nominal maximum size weight aggregate concrete which should be provided of aggregate or the maximum size of bars, to all reinforcement, including links depending.on the whichever is greater. condition of exposure described in 8.2.3 shall be as26.3.3 Maximum Distance Between Bars in Tension given in Table 16.Unless the calculation of crack widths shows that a However for a longitudinal reinforcinggreater spacing is acceptable, thefollowing rules shall bar in a column nominal cover shall in any case notbe applied to flexural members in normal internal or be less than 40 mm, or less than the diameter dfexternal conditions of exposure. such bar. In the case of columns of minimum dimension of 200 mm or under, whose reinforcing bars a) Beams - The horizontal distance between do not exceed 12 mm, a nominal cover of 25 mm may parallel reinforcement bars, or groups, near the be used. tension face of a beam shall not be greater than the value given in Table 15 depending on For footings_minirnumcover shall be 50 mm. the amount of redistribution carried out in 26.4.3 Nominal Cover to Meet S’cified Period of analysis and the characteristic strength of the Fire Resistance reinforcement. Minimum values of nominal cover of normal-weight b) Slabs aggregate concrete to be provided to all reinforcement including links to meet specified period of fire 1) The horizontal distance between parallel main resistance shall be given in Table %A. reinforcement bars shall not be more than three times thl effective depth of solid slab or 265 Requirements of Reinforcement for 300 mm whichever is smaller. Structural Members 2) The horizontal distance between parallel 26.5.1 Beams reinforcement bars provided against Tension reinforcement shrinkage and temperature shall not be more than five times the effective depth of a solid a) Minimum reinfoKement-Theminimum area of slab or 450 mm whichever is smaller. tension reinforcement shall be not less than-that Table 15 Clear Distance Between Bars (Clause 26.3.3) f, mtage ikedIstributIonto or tram Section Gmtddered - 30 I - 15 I 0 I + 15 I +30 Clew D&awe Behveen BarsNhl? mm mm mm 250 215 260 350 415 125 155 180 500 105 130 150 NOTE-The spacings given in the tublenrenot applicableto memberssubjectedto particularly~nggrcssivc environment8 inthe unless calcuhtion of the momentof rtsistunce.f, has been limitedto 300 Nhnn? in limit state design und u, limited to 165 N/mm’ in wo&ii stress design. 46
  • IS 456 : 2000 Table 16 Nominal Cover to Meet Durability Requirements (Clause 26.4.2) Exposure Nominal Concrete Cover in mm not Less Than Mild 20 Moderate 30 Severe 45 Very severe 50 Extreme 75 NOTES 1 For main reinforcement up to 12 mm diameter bar for mild exposure the nominal cover may be reduced by 5 mm. 2 Unless specified otherwise, actual concrete cover should not deviate from the required nominal cover by +I0 mm 0 3 For exposure condition ‘severe’ and ‘very severe’, reduction of 5 mm may be made, where cpncrete grade is M35 and above. Table 16A Nominal Cover to Meet Specified Period of Fire Resistance (Clauses 21.4-and 26.4.3 and Fig. 1)Fire Nominal CoverReSiS-tance Beams Slabs Ribs Columns Simply Continuous Simply Continuous Simply Continuous supported supported supportedh mm mm mm mm mm mm mm0.5 20 20 20 20 20 20 401 20 20 20 20 20 20 401.5 20 20 25 20 3 20 402 40 30 P 25 45 ;tz 403 60 40 45 X 55 *5 404 70 50 55 45 65 55 40 NOTES 1 The nominal covers given relate specifically to the minimum member dimensions given in Fig. 1. 2 Cases that lie below the bold line require attention to the additional measures necessary to reduce the risks of spalling (see 213.1). given by the following: Side face reinforcement 0.85 Where the depth of the web in a beam exceeds 750 mm, A, side face reinforcement shall be provided along the two bd=fy faces. The total area ofsuch reinforcement shall be notwhere less than 0.1 percent of the web area and shall be distributed equally on two faces at a spacing AS = minimum area of tension reinforcement, not exceeding 300 mm or web thickness whichever is b = breadth of beam or the breadth of the web less. of T-beam, Transverse reinforcement in beams for shear d = effective depth, and and torsion f, = characteristic strength of reinforcement in The transverse reinforcement in beams shall be taken N/mmz. around the outer-most tension and compression bars. b) Maximum reinfonzement-lhe maximum area of In T-beams and I-beams, such reinforcement shall pass around longitudinal bars located close to the outer face tensionreinforcementshalInot exceed 0.04 bD. of the flange. Compression reinforcement Maximum spacing of shear reinfomementThe maximum area of compression reinforcementshall not exceed 0.04 bD. Compression reinforcement The maximum spacing of shear reinforcementin beams shall be enclosed by stirrups for effective measured along the axis of the member shall not exceedlateral restraint. The arrangement of stirrups shall be 0.75 d for vertical stirrups and d for inclined sti?rupsas specified in at 45”, where d is the effective depth of the section 47
  • IS 456 : 2ooounder consideration. In no case shall the spacing 26.52 sklbsexceed 300 mm. The rules given in and shall apply26.5.1.6 Minimum shear reinforcement to slabs in addition to those given in the appropriateMinimum shear reinforcement in the form of stirrups clauses.shall be provided such that: Minimum reinforcement 4 vz- 0.4 The mild steel reinforcement in either direction in slabs bs, 0.87 fy shall not be less than 0.15 percent of the total cross- sectional area. However, this value can be reduced towhere 0.12 percent when high strength deformed bars or AS” = total cross-sectional area of stirrup legs welded wire fabric are used. effective in shear, 26.5.22 Maximum diameter s” = stirrup spacing along the length of the The diameter of reinforcing bars shall not exceed one- member, eight of the total thickness of the slab. b = breadth of the beam or breadth of the web of flanged beam, and 26.5.3 columns f, = characteristic strength of the stirrup Longitudinal reinforcement reinforcement in N/mm* which shall not a) The cross-sectional area of longitudinal be taken greater than 415 N/mn?. reinforcement, shall be not less than 0.8 percentWhere the maximum shear stress calculated is less than nor more than 6 percent of the gross cross-half the permissible value and in members of minor sectional area of the column.structural importance such as lintels, this provision NOTE - The use of 6 percentreinforcementmay involveneed not be complied with. practicaldiffkulties in placing and compactingof concrete; hence lower percentageis recommended. Wherebarsfrom26.5.1.7 Distribution-of torsion reinforcement the columns below have to be lapped with those in the column under consideration,the percentageof steel shallWhen a member is designed for torsion (see 41 or usually not exceed 4 percent.B-6) torsion reinforcement shall be provided as below: b) In any column that has a larger cross-sectional a) The transverse reinforcement for torsion shall area than that required to support the load, be rectangular closed stirrups placed perpen- the minimum percentage of steel shall be dicular to the axis of the member. The spacing based upon the area of concrete required to of the stirrups shall not exceed the least of resist the~direct stress and not upon the actual Xl +Yl area. -5 - 4 and 300 mm, where xi and y, are The minimum number of longitudinal bars cl respectively the short and long dimensions of providedinacolumnshallbefourinrectangular the stirrup. columns and six in circular columns. b) Longitudinal reinforcement shall be placed as 4 The bars shall not be less than 12 mm in close as is practicable to the comers of the cross- diameter. section and in all cases, there shall be at least e) A reinforced concrete column having helical one longitudinal bar in each comer of the ties. reinforcement shall have at least six bars of When the cross-sectional dimension of the longitudinal reinforcement within the helical member exceeds 450 mm, additional reinforwment. longitudinal bats&all he provided to satisfy the f) In a helically reinforced column, the longitudinal requirements of minimum reinforcement and bars shall be in contact with the helical spacing given in 26.5.13. reinforcement and equidistant around its inner26.5.1.8 Reinforcement in flanges of T-and L-beams circumference.shall satisfy the requirements in 23.1.1(b). Where 8) Spacing of longitudinal bars measured alongflanges are in tension, a part of the main tension the periphery of the column shall not exceedreinforcement shall be distributed over the effective 300 mm.flange width or a width equal to one-tenth of the span, h) In case of pedestals in which the longitudinalwhichever is smaller. If the effective flange width reinforcement is not taken in account in strengthexceeds one-tenth of the span, nominal longitudinal calculations, nominal longitudinal reinforcementreinforcement shall be provided in the outer portions not less than 0.15 percent of the cross-sexonalof the flange. area shall be provided. 48
  • IS 456 : 2000 NOTE - Pedestal is a compression member, the effective reinforcement need not, however, exceed length of which does not exceed three times the least lateral 20 mm (see Fig. 11). dimension. c) Pitch and diameter of lateral ties26.5.3.2 Transverse reinforcement 1) Pitch-The pitch of transverse reinforce- a>General-A reinforced concrete compression ment shall be not more than the least of the member shall have transverse or helical following distances: reinforcement so disposed that every longitu- dinal -bar nearest to the compression face i) The least lateral dimension of the has effective lateral support against buckling compression members; subject to provisions in (b). The effective lateral ii) Sixteen times the smallest diameter of support is given by transverse reinforcement the longitudinalreinforcement bar to be either in the form of circular rings capable of tied; and taking up circumferential tension or by iii) 300 mm. polygonal links (lateral ties) with internal angles not exceeding 135’. The ends of the transverse 2) Diameter-The diameter of the polygonal reinforcement shall be properly anchored links or lateral ties shall be not less than one- [see (b)]. fourth of the diameter of the largest longitudinal bar, and in no case less than b) Arrangement of transverse reinforcement 16 mm. 1) If the longitudinal bars are not spaced more d) Helical reinforcement than 75 mm on either side, transverse reinforcement need only to go round comer 1) Pitch-Helical reinforcement shall be of and alternate bars for the purpose of regular formation with the turns of the helix providing effective lateral supports spaced evenly and its ends shall be anchored (see Fig. 8). properly by providing one and a half extra turns of the spiral bar. Where an increased 2) If the longitudinal bars spaced at a distance of not exceeding 48 times the diameter of load on the column on the strength of the the tie are effectively tied in two directions, helical reinforcement is allowed for, the pitch additional longitudinal bars in between these of helical turns shall be not more than 7.5mm, bars need to be tied in one direction by open nor more than one-sixth of the core diameter ties (see Fig. 9). of the column, nor less than 25 mm, nor less than three times the diameter of the steel bar 3) Where the longitudinal reinforcing bars in forming the helix. In other cases, the a compression member are placed in more requirements of shall be complied than one row, effective lateral support to the with. longitudinal bars in the inner rows may be assumed to have been provided if: 2) The diameter of the helical reinforcement shall be in accordance with (c) (2). i> transverse reinforcement is provided for the outer-most row in accordance with ln columns where longitudinal bars are offset, and at a splice, the slope of the inclined portion of the bar with the axis of the column shall not exceed 1 in 6, ii) no bar of the inner row is closer to the and the portions of~thebar above and below the offset nearest compression face than three shall be parallel to the axis of the column. Adequate times the diameter of the largest bar in horizontal support at the offset bends shall be treated the inner row (see Fig. 10). as a matter of design, and shall be provided by metal 4) Where the longitudinal bars in a com- ties, spirals, or parts of the floor construction. Metal pression member are grouped (not in ties or spirals so designed shall be placed near (not contact) and each group adequately tied with more than eight-bar diameters from) the point of bend. transverse reinforcement in accordance with The horizontal thrust to be resisted shall be assumed, the transverse reinforcement for the as one and half times the horizontal components of compression member as a whole may be the nominal stress in the inclined portion of the bar. provided on the assumption that each group Offset bars shall be bent before they are placed in the is a single longitudinal bar for purpose of forms. Where column faces are offset 75 mm or more, determining the pitch and diameter of the splices of vertical bars adjacent to the offset face shall transverse reinforcement in accordance with be made by separate dowels overlapped as specified The diameter of such transverse in 49
  • IS 456 : 200027 EXPANSION JOINTS 27.2 The details as to the length of a structure where expansion joints have to be provided can be determined27.1 Structures in which marked changes in plan after taking into consideration various factors, such asdimensions take~place abruptly shall be provided with temperature, exposure to weather, the time and seasonexpansion on joints at the section where such changes of the laying of the concrete, etc. Normally structuresoccur. Expansion joints shall be so provided that the exceeding 45 m in length are designed with one nornecessary movement occurs with a minimum more expansion joints. However in view of the largeresistance at the joint. The structures adjacent to the number of factors involved in deciding the location,joint should preferably be supported on separate spacing and nature of expansion joints, the provisioncolumns or walls but not necessarily on separate of expansion joint in reinforced cement concretefoundations. Reinforcement shall not extend across structures should be left to the discretion of thean expansion joint and the break between the sections designer. IS 3414 gives the design considerations, shall be complete. which need to be examined and provided for. All dimensions in millimetres. All dimensions in millimetres. FIG. ~8 FIG. 9 TTRANSVERSE REINFORCEMENT b-1 /DIAMETER (I u I INDIVIDUAL GROUPS All dimensions in millimetms. FIG. 11 FIG. 10 50
  • IS 456 : 2000 SECTION 4 SPECIAL DESIGN -REQUIREMENTS FOR STRUCTURAL MEMBERS~AND. SYSTEMS28 CONCRETE CORBELS 28.2.4 Resistance to Applied Horizontal Force28.1 General Additional reinforcement connected to the supported member should be provided to transmit this force inA corbel is a short cantilever projection which supports its entirety.a load bearing member and where: a>the distance aVbetween the line of the reaction 29 DEEP BEAMS to the supported load and the root of the corbel 29.1 General is less than d (the effective depth of the root of the corbel); and a) A beam shall be deemed to be a deep beam when b) the depth af the outer edge of the contact area the ratio of effective span to overall depth, i of the supported load is not less than one-half of the depth at the root of the corbel. is less than:The depth of the corbel at the face of the support is 1) 2.0 for a simply supported beam; anddetermined in accordance with 4O;S.l. PD 2) 2.5 for a continuous beam.28.2 Design b) A deep beam complying with the requirements of 29.2 and 29.3 shall be deemed to satisfy the28.2.1 SimplijjGng Assumptions provisions for shear.The concrete and reinforcement may be assumed to 29.2 Lever Armact as elements of a simple strut-and-tie system, withthe following guidelines: The lever arm z for a deep beam shall be detemined as 4 The magnitude of the resistance provided to below: horizontal force should be not less than one-half For simply supported beams: of the design vertical load on the corbel (see also 28.2.4). z = 0.2 (1+ 20) whenlS$<2 b) Compatibility of strains between the strut-and- or tie at the corbel root should be ensured. 1 z = 0.6 1 when - <1It should be noted that the horizontal link requirement Ddescribed in 28.2.3 will ensure satisfactory service- b) For continuous beams:ability performance.28.2.2 Reinforcement Anchorage z = 0.2(1+1.5D) when 1 I iS2.5At the front face of the corbel, the reinforcement should orbe anchored either by: 1 z = 0.5 1 when - <1 a>welding to a transverse bar of equal strength - D in this case the bearing area of the load should where 1is the effective span taken as centm to centre stop short of the face of the support by a distance distancebetween supportsor 1.15times the clear span, equal to the cover of the tie reinforcement, or whichever is smaller, and D is the overall depth. b) bending back the bars to form a loop - in this 29.3 Reinforcement case the bearing area of the load should not project beyond the straight ~portion of 29.3.1 Positive Reinforcement the bars forming the main tension reinforcement. The tensile reinforcement required to resist positive bending moment in any span of a deep beam~shall: 28.2.3 Shear Reinforcement Shear reinforcement should be provided in the form a) extend without curtailment between supports; of horizontal links distributed in the upper two-third b) be embedded beyond the face of each support, of the effective depth of root of the corbel; this so that at the face of the support it shall have a reinforcement should be not less than one-half of the development length not less than 0.8 L,,; where area of the main tension reinforcement and should be LJ is the development length (see 26.2.1), for adequately anchored. the design stress in the reinforcement; and 51
  • IS 456 : 2000 c) be placed within a zone of depth equal to structure; the top of the ribs may be connected 0.25 D - 0~05 1 adjacent to the tension face of by a topping of concrete of the same strength as the beam where D is the overall depth and 1 is that used in the ribs; and the effective span. c) With a continuous top and bottom face but29.3.2 Negative Reinforcement containing voids of rectangular, oval or 4 Termination of reinforcement - For tensile other shape. reinforcement required to resist negative bending moment over~a support of a deep beam: 30.2 Analysis of Structure 1) It shall be permissible to terminate not more The moments and forces due to design loads on than half of the reinforcement at a distance continuous slabs may he obtained by the methods given of 0.5 D from the face of the support where in Section 3 for solid slabs. Alternatively, the slabs D is as defined in 29.2; and may be designed as a series of simply supported spans 2) The remainder shall extend over the full provided they are not exposed to weather or corrosive span. conditions; wide cracks may develop at the supports and the engineer shall satisfy himself that these will b) Distribution-When ratio of clear span to overall depth is in the range 1.0 to 2.5, tensile not impair finishes or lead to corrosion of the reinforcement over a support of a deep beam reinforcement. shall be placed in two zones comprising: 30.3 Shear 1) a zone of depth 0.2 D, adjacent to the tension face, which shall contain a proportion of the Where hollow blocks are used, for the purpose tension steel given by of calculating shear stress, the rib width may be increased to take account of the wall thickness of thewhere 0.5 ( ; - 0.5 1 block on one side of the rib; with narrow precast units, the width of the jointing mortar or concrete may be included. 1 = clear span, and D = overall depth. 30.4 Deflection 2) a zone measuring 0.3 D on either side of The recommendations for deflection in respect of solid the mid-depth of the beam, which shall slabs may be applied to ribbed, hollow block or voided contain the remainder of the tension steel, construction. The span to effective depth ratios given evenly distributed. in 23.2 for a flanged beam are applicable but when For span to depth ratios less than unity, the calculating the final reduction factor for web width, the rib width for hollow block slabs may be assumed steel shall be evenly distributed over a to include the walls of the blocks on both sides of the depth of 0.8 D measured from the tension face. rib. For voided slabs and slabs constructed of box or I-section units, an effective rib widthshall be calculated29.3.3 Vertical Reinforcement assuming all material below the upper flange of theIf forces are applied to a deep beam in such a way that unit to be concentrated in a rectangular rib having thehanging action is required, bars or suspension stirrups same cross-sectional area and depth.shall be provided to carry all the forces concerned. 30.5 Size and Position of Ribs 29.3.4 Side Face Reinforcement In-situ ribs shall be not less~than 65 mm wide. They Side face reinforcement shall comply with require- shall be spaced at centres not greater than 1.5 m apart ments of minimum reinforcement of walls (see 32.4). and their depth, excluding any topping, shall be not 30 RIBBED, HOLLOW BLOCK ORVOIDED SLAB more than four times their width. Generally ribs shall be formed along each edge parallel to the spanof one 30.1 General way slabs. When the edge is built into a wall or rests This covers the slabs constructed in one of the ways on a beam, a rib at least as wide as~the bearing shall be described below: formed along the edge. a) As a series of concrete ribs with topping cast on forms which may be removed after the concrete 30.6 Hollow Blocks and Formers has set; Blocks and formers may be of any suitable material. ~b) As a series of concrete ribs between precast Hollow clay tiles for the filler~type shall conform to blocks which remain part of the completed IS 3951 (Part 1). When required to contribute to the 52
  • . IS 456 : 2000structural strength of a slab they shall: to 1,, measured centre to centre of supports. a) be~made of concrete or burnt clay; and b) Middle strip -Middle strip means a design strip b) have a crushing strength of at least 14 N/mm* bounded on each of its opposite sides by the measured on the net section when axially loaded column strip. in the direction of compressive stress in the slab. cl Panel-Panel means that part of a slab bounded on-each of its four sides by the centre-line of a30.7 Arrangement of Reinforcement column or centre-lines of adjacent-spans.The recommendations given in 26.3 regarding 31.2 Proportioningmaximum distance between bars apply to areas of solidconcrete in this form of construction. The curtailment, 31.2.1 Thickness of Flat Slabanchorage and cover to reinforcement shall be as The thickness of the flat slab shall be generallydescribed below: controlled by considerations of span to effective depth 4 At least 50 percent of the total main ratios given in 23.2. reinforcement shall be carried through at the For slabs with drops conforming to 31.2.2, span to bottom on to the bearing and anchored in effective depth ratios given in 23.2 shall be applied accordance with directly; otherwise the span to effective depth ratios b) Where a slab, which is continuous over supports, obtained in accordance with provisions in 23.2 shall has been designed as simply supported, be multiplied by 0.9. For this purpose, the longer span reinforcement shall be provided over the support shall be considered. The minimum thickness of slab to control cracking. This reinforcement shall shall be 125 mm. have a cross-sectional area of not less than one- quarter that required in the middle of the 31.2.2 Drop adjoining spans and shall extend at least one- The drops when provided shall be rectangular in plan, tenth of the clear span into adjoining spans. and have a length in each direction not less than one- c) In slabs with permanent blocks, the side cover third of the panel length in that direction. For exterior to the reinforcement shall not be less than panels, the width of drops at right angles to the non- 10 mm. In all other cases, cover shall be continuous edge and measured from the centre-line of provided according to 26.4. the columns shall be equal to one-half the width of drop for interior panels.30.8 Precasts Joists and Hollow Filler Blocks 31.2.3 Column HeadsThe construction with precast joists and hollowconcrete filler blocks shall conform to IS 6061 (Part Where column heads are provided, that portion of a1) and precast joist and hollow clay filler blocks shall column head which lies within the largest right circularconform to IS 6061 (Part 2). cone or pyramid that has a vertex angle of 90”and can be included entirely within the outlines of the column31 FLAT SLABS and the column head, shall be considered for design purposes (see Fig. 12).-31.1 General 31.3 Determination of Bending MomentThe term flat slab means a reinforced concrete slabwith or without drops, supported generally without 31.3.1. Methods of Analysis and Designbeams, by columns with or without flared column It shall be permissible to design the slab system byheads (see Fig. 12). A flat slab~may be solid slab or one of the following methods:may have recesses formed on the soffit so that the soflit a) The direct design method as specified in 31.4,comprises a series of ribs in two directions. The andrecesses may be formed~by removable or permanent b) The equivalent frame method as specifiedfiller blocks. in 31.5. 31.1.1 For the purpose of this clause, the following In each case the applicable limitations given in 31.4 definitions shall apply: and 31.5 shall be met. a) Column strip -Column strip means a design 31.3.2 Bending Moments in Panels with Marginal strip having a width of 0.25 I,, but not greater Beams or Walls than 0.25 1, on each side of the column centre- line, where I, is the span in the direction Where the slab is supported by a marginal beam with moments are being determined, measured centre a depth greater than 1.5 times the thickness of the slab, to centre of supports and 1,is the-span transverse or by a wall, then: 53
  • .IS 456 : 2000 CRlTlCAL~SECflON CRITICAL SECTION 12A SLAB WITHOUT DROP A COLUMN WITHOUT COLUMN HEAD CRITICAL SECTION FOR SHEAR 12 B SLAB WITH DROP L COLUMN WITH COLUMN HEAD ANY CONCRETE IN THIS ARIA TO BE NEGLECTED IN THE CALCULATIONS SLAB WITHOUT DROP & COLUMN WITH COLUMN HEAD NOTE - D, is the diameter of column or column head to be considered for design and d is effective depth of slab or drop as appropriate. FIG. 12 CRITICAL SUJI~ONS FOR SHEAR FLAT IN SLABS a) the total load to be carried by the beam or wall A slab width between lines that are one and one-half shall comprise those loads directly on the wall slab or drop panel thickness; 1.5 D, on each side of or beam plus a uniformly distributed load-equal the column or capital may be considered effective, D to one-quarter of the total load on the slab, and being the size of the column. b) the bending moments on the~half-column strip Concentration of reinforcement over column head by adjacent to the beam or wall shall be one-quarter closer spacing or additional reinforcement may be used of the bending moments for the first interior to resist the moment on this section: column strip. 31.4 Direct Design Method 31.3.3 Transfer of Bending Moments to Columns 31.4.1 LimitationsWhen unbalanced gravity load, wind, earthquake, or Slab system designed by the direct design method shallother lateral loads cause transfer of bending moment fulfil the following conditions:between slab and column, the flexural stresses shallbe investigated using a fraction, CL the moment given of 4 There shall be minimum of three continuousby: spans in each direction, b) The panels shall be rectangular, and the ratio of the longer span to the shorter span within a panel a=.&7 Ql shall not be greater than 2.0, a2 c) It shall be permissible to offset columns to a where maximum of 10 ~percent of the span in the 5 = overall dimension of the critical section direction of the offset notwithstanding the for shear in the direction in which provision in (b), moment acts, and d) The successive span lengths in each direction a2 = overall dimension of the critical section shall not differ by more than one-third of the for shear transverse to the direction in longer span. The end spans may be shorter but which moment acts. not longer than the interior spans, and 54
  • I!S456:2000 e) The design live load shall not exceed three times Exterior negative design moment: the design dead load. 0.6531.4.2 Total Design Moment for a Span l+L31.4.2.1 In the direct design method, the total design cr,moment for a span shall be determined for a strip a, is the ratio of flexural stiffness of the exteriorbounded laterally by the centre-line of the panel oneach side of the centre-line of the supports. columns to the flexural stiffness of the slab at a joint taken in the direction moments are being determined31.4.2.2 The absolute sum of the positive and average and is given bynegative bending moments in each direction shall betaken as: where K, = sum of the flexural stiffness of the total moment; columns meeting at the joint; and 4, = w= design load on an area 1, 1"; _K, = flexural stiffness of the slab, expressed as moment per.unit rotation. 1. = clear span extending from face to face of columns, capitals, brackets or walls, but It shall be permissible to modify these design not less than 0.65 1,; moments by up to 10 percent, so long as the total design 1, = length of span in the direction of M,,; and moment, M,, for the panel in the direction considered is not less than that required by 1, = length of span transverse to 1,. The negative moment section shall be31.4.2.3 Circular supports shall be treated as square designed to resist~thelarger of the two interior negativesupports having the same area. design momenta determined for the spans framing into3X4.2.4 When the transverse span of the panels on a common support unless an analysis is made toeither side of the centre-line of supports varies, I, shall distribute the unbalanced moment in accordance withbe taken as the average of the transverse spans. the stiffness of the adjoining parts. When the span adjacent and parallel to attedgeis being considered, the distance from the edge to the 31.4.4 Distribution of Bending Moments Across thecentre-line of the panel shall be substituted for 1, Panel Wdthifi Bending moments at critical cross-section shall -be distributed to the column strips and middle strips as31.4.3 Negative and Positive Design Moments specified in 31.55 as applicable. The negative design moment shall be locatedat the face of rectangular supports, circular supports 31.4.5 Moments in Columnsbeing treated as square supports having the same Columns built integrally with the slab systemarea. shall be designed to-resist moments arising from loads31.4.3.2 In an interior span, the total design moment on the slab system.M,,shall be distributed in the following proportions: At an interior support, the supporting Negative design moment 0.65 members above and below the-slab shall be designed Positive design moment 0.35 to resist the moment M given by the following equation, In an end span, the total design moment MO in direct proportion to their stiffnesses unless a generalshall be distributed in the following proportions: analysis is made:Interior negative design moment: (W” -w: +0.5w,)1,1.’ 1: 1:’ M = 0.08 1 where Positive design moment: Wd,~W, design dead and live = loads 0.28 respectively, per unit area; 0.63-- l+’ 1, = length of span transverse to the a, direction of M, 55
  • IS 456 : 2000 1, = length of the clear span in the b) Each such frame may be analyzed in its entirety, direction of M, measured face to face or, for vertical loading, each floor thereof and of supports; the roof may be analyzed separately with its columns being assumed fixed at their remote XK a, = C where K, and KSare as defined ends. Where slabs are thus analyzed separately, =KS it may be assumed in determining the bending in; and moment at a given support that the slab is fixed w:, l’, and li, refer to the shorter span. at any support two panels distant therefrom provided the slab continues beyond the point.31.4.6 Effects of Pattern-Loading cl For the purpose of determining relative stiffnessIn the direct design method, when the ratio of live load of members, the moment of inertia of any slabto dead load exceeds 0.5 : or column may be assumed to be that of the gross cross-section of the concrete alone. 4 the sum of the flexural stiffnesses of the columns above and below the slab, mC, shall be such 4 Variations of moment of inertia along theaxis that CL, not less than the appropriate minimum is of the slab on account of provision of drops shall value aC min specified in Table 17, or be taken into account. In the case of recessed or coffered slab which is made solid in the b) if the sum of the flexural stiffnesses of the region of the columns, the stiffening effect may columns, XC, does not satisfy (a), the positive be ignored provided the solid part of the slab design moments for the panel shall be multiplied does not extend more than 0.15 Zti, into the span by the coefficient /I, given by the following measured from the centre-line of the columns. equation: ‘Ihe stiffening effect of flared column heads may be ignored. 31.52 Loading Pattern When the loading pattern is known, the structure shall be analyzed for the load~concerned,01,is the ratio of flexural stiffness of the columns above Table 17 Minimum Permissible Values of c1,and below the slab to the flexural stiffness of the slabs (Chue 31.4.6)at a joint taken in the direction moments are beingdetermined and is given by: ImposedLoad/Dead Load Ratio + Value of a= II. (1) (2) ’ (3) 0.5 0.5 to 2.0 0 1.0 0.5 0.6where K, and KSare flexural stiffnesses of column and 1.0 0.8 0.7slab respectively. 1.0 1.0 0.7 1.0 1.25 0.831.5 Equivalent Frame Method 1.0 2.0 Assumptions 2.0 0.5 1.3 2.0 0.8 1.5The bending moments and shear forces may be 2.0 1.0 1.6determined by an analysis of the structure as a 2.0 1.25 1.9continuous frame and the following assumptions may 2.0 2.0 4.9be made: 3.0 0.5 1.8 3.0 0:8 2.0 a) The structure shall be considered to be made up 3.0 1.0 2.3 of equivalent frames on column lines taken 3.0 1.25 2.8 longitudinally and transversely through the 3.0 2.0 13.0 building. Each frame consists of a row of equivalent columns or supports, bounded When the live load is variable but does not laterally by the centre-line of the panel on each exceed three-quarters of the dead load, or the nature side of the centre-line of the columns or of the live load is such that all panels will be loaded supports. Frames adjacent’andparallel to an edge simultaneously, the maximum moments may be shall be bounded by the edge and the centre- assumed to occur at all sections when full design live line of the adjacent panel. load is on the entire slab system. 56
  • IS456:200031.5.2.3 For other conditions of live load/dead load greater than three-quarters of the value of 1,.theratio and when all panels are not loaded simultaneously: length of span transverse to the direction 4 maximum positive moment near midspan of a moments are being determined, the exterior panel may be assumed to occur when three- negative moment shall be considered to be quarters of the full design live load is on the uniformly distributed across the length I,. panel and on alternate panels; and Column strip : Positive momentfor each span b) maximum negative moment in the slab at a For each span, the column strip shall be designed to support may be assumed to occur when three- resist 60 percent of the total positive moment in the quarters of the full design live load is on the panel. adjacent panels only. Moments in the middle strip3- In no case shall design moments be taken to The middle strip shall be designed on the followingbe less than those occurring with full design live load bases:on all panels. 4 That portion of-the design moment not resisted31.53 Negative Design Moment by the column strip shall be assigned to the31.5.3.1 At interior supports, the critical section for adjacent middle strips.negative moment, in both the column strip and middle b) Each middle strip shall be proportioned to resiststrip, shall be taken at the face of rectilinear supports, the sum of the moments assigned to its two halfbut in no case at a distance greater than 0.175 1, from middle strips.the centre of the column where 1, is the length of the cl The middle strip adjacent and parallel to an edgespan in the direction moments are being determined, supported by a wall shall be proportioned, tomeasured centre-to-centre of supports. resist twice the moment assigned to half the31.5.3.2 At exterior supports provided with brackets middle strip corresponding to the first row ofor capitals, the critical section for negative moment in interior columns.the direction perpendicular to the edge shall be taken 31.6 Shear in Nat Slabat a distance from the face of the supporting elementnot greater than one-half the projection of the bracket 31.6.1 ‘Ike critical section for shear shall be at aor capital beyond the face of the supporting element. distance d/2 from the periphery of the column/capital/ drop panel, perpendicular to the plane of the slab where31.5.3.3 Circular or regular polygon shaped supports d is the effective depth of the section (see Fig. 12).shall be treated as square supports having the same The shape in plan is geometrically similar to the supportarea. immediately below the slab (see Fig. 13A and 13B).31.54 Modification of Maximum Moment NOTE-For columnsectionswith reentrantangles, the critical section shall be taken ils indicated in Fig. 13C and 13D.Moments determined by means of the equivalent frame In the case of columns near the free edge ofmethod, for slabs which fulfil the limitations of 31.4 a slab, the critical section shall be taken as shown inmay be reduced in such proportion that the numerical Fig. 14.sum of the positive and average negative moments isnot less than the value of total design moment M,, When openings in flat slabs are located at aspecified in distance less than ten times the thickness of the slab from a concentrated reaction or when the openings are31.55 Distribution of Bending Moment Across the located within the column strips, the critical sectionsPanel Width specified in 31.6.1 shall be modified so that the part of31.5.5.1 Column strip : Negative moment at an interior the periphery of the critical section which is enclosedsupport by radial projections of the openings to the centroid of the reaction area shall be considered ineffectiveAt an interior support, the column strip shall be (see Fig. 15), and openings shall not encroach upondesigned to resist 75 percent of the total negative column head.moment in the panel at that support. Column strip : Negative moment at an exterior 31.6.2 Calculation of Shear Stresssupport The shear stress 2, shali be the sum of the values 4 At an exterior support, the column strip shall be calculated according to and designed to resist the total negative moment in The nominal shear stress in flat slabs shall be the panel at that support. taken as VI b,,dwhere Vis the shear force due to design b) Where the exterior support consists of a column load, b,, is the periphery of the critical section and d is or a wall extending for a distance equal to or the effective depth. 57
  • IS 456 : 2000 r--------i r CRITICAL SECT ‘ION SUPPORT SECTION LSUPPORT SEbTlbN COLUMN I COLUMN HEAD 13A CRITICAL SECTION-J K%FIT L-- --_-_I df2 13D 7- , NOTE-d is the effective depth of the flat slab/drop. FIG. 13 CR~TKAL SECTIONS PLANFOR IN SHIZAR FLAT IN SLABS FREE CORNER 14 A FIG. 14 Errzcr OFFREEEDGES CRITICAL ON SK~ION SHEAR FOR31.6.2.2 When unbalanced gravity load, wind, value of a shall be obtained from the equation givenearthquake or other forces cause transfer of bending in 31.3.3.moment between slab and column, a fraction (1 - o!j 31.6.3 Pemissible Shear Stressof the moment shall be considered transferred byeccentricity of the shear about the centroid of the When shear reinforcement is not provided,critical section. Shear stresses shall be taken as varying the calculated shear stress at the critical section shalllinearly about the centroid of the critical section. The not exceed $T~, 58
  • IS 456 : 2000 SUBTRACT FROM OPENING -$--j-- PERIPHERY LARGE OPENNG+ i i Y REGARD OPENING AS FREE EDGE 15c 15D FIG. 15 EFFKTOFOPENINGS CRITICAL ON SECTION SHEAR FORwhere 2 times the slab thickness, except where a slab is of k, = (0.5 + &) but not greater than 1, PCbeing the cellular or ribbed construction. ratio of short side to long side of the column/ 31.7.2 Area of Reinforcement capital; and When drop panels are used, the thickness of drop panel r, = 0.25 & in limit state method of design, for determination of area of~reinforcement shall be the lesser of the following: and 0.16 & in working stress method of a) Thickness of drop, and design. b) Thickness of slab plus one quarter the distance31.6.3.2 When the shear stress at the critical section between edge of drop and edge of capital.exceeds the value given in, but less than1.5 2, shear reinforcement shall be provided. If the 31.7.3 Minimum Length of Reinforcementshear stress exceeds 1.5 T,, the flat slab shall be a) Reinforcement in flat slabs shall have theredesigned. Shear stresses shall be investigated at minimum lengths specified in Fig.16. Largersuccessive sections more distant from the support and lengths of reinforcement shall be provided whenshear reinforcement shall be provided up to a section required by analysis.where the shear stress does not exceed 0.5 z,. While b) Where adjacent spans are unequal, the extensiondesigning the shear reinforcement, the shear stress of negative reinforcement beyond each face of the common column shall be based on the longercarried by the concrete shall be assumed to be 0.5 2, span.and reinforcement shall carry the remaining shear. cl The length of reinforcement for slabs in frames31.7 Slab Reinforcement not braced against sideways and for slabs resisting lateral loads shall be determined by31.7.1 Spacing analysis but shall not be less than thoseThe spacing of bars in a flat slab, shall not exceed prescribed in Fig. 16. 59
  • IS456: REMAINOER REMAINMR REMAINDER REMAINDER (NO S&A8 CONTINUIIYI ICON1INUITY lROVlOEOb INO sLA8 CONTlNUtl Bar Lengthfrom Face of Support Mininwn Length Maximum Length Mark a b C d E f g Length 0.14 lD 0.20 1, 0.22 1. 0.30 1. 0.33 1. 0.20 la 0.24 l,, 1 * Bent bars at exteriorsupportsmay be used if u general analysis is made. NOTE - D is the diameterof the column and the dimension of the rectangular column in the directionunder consideration. FIG. 16 MINIMUM BENDJOINT LOCATIONS EXTENSIONS RENWRCEMEN AND FOR INFLATSLABS 60
  • IS 456 : 200031.7.4 Anchoring Reinforcement as per empirical procedure given in 32.2. The minimum thickness of walls shall be 100 mm. a) All slab reinforcement perpendicular to a discontinuous edge shall have an anchorage 32.1.1 Guidelines or design -of walls subjected to (straight, bent or otherwise anchored) past the horizontal and vertical loads are given in 32.3. internal face of the spandrel beam, wall or 32.2 Empirical Design Method for Walls Subjected column, of an amount: to Inplane Vertical Loads 1) For positive reinforcement - not less than 32.2.1 Braced Walls 150 mm except that with fabric reinforce- ment having a fully welded transverse wire Walls shall be assumed to be braced if they are laterally directly over the support, it shall be supported by a structure in which all the following permissible to reduce this length to one-half apply: of the width of the support or 50 mm, a>Walls or vertical braced elements are arranged whichever is greater; and in two directions so as to provide lateralstability to the structure as a whole. 2) For negative reinforcement - such that the design stress is developed at the internal b) Lateral forces are resisted by shear in the planes face, in accordance with Section 3. of these walls or by braced elements. b) Where the slab is not supported by a spandrel c>Floor and roof systems are designed to transfer beam or wall, or where the slab cantilevers lateral forces. beyond the support, the anchorage shall be 4 Connections between the wall and the lateral obtained within the slab. supports are designed to resist a horizontal force not less than31.8 Openings in Flat Slabs 1) the simple static reactions to the total appliedOpenings of any size may be provided in the flat slab horizontal forces at the level of lateralif it is shown by analysis that the requirements of support; andstrength and serviceability are met. However, foropenings conforming to the following, no special 2) 2.5 percent of the total vertical load that theanalysis is required. wall is designed to carry at the level of lateral support. 4 Openings of any size may be placed within the middle half of the span in each direction, 32.2.2 Eccentricityof Vertical Load provided the total amount of reinforcement The design of a wall shall take account of the actual required for the panel without the opening is eccentricity of the vertical force subject to a minimum maintained. value of 0.05 t. b) In the area common to two column strips, not The vertical load transmitted to a wall by a more than one-eighth of the width of strip in discontinuous concrete floor or roof shall be assumed either span shall be interrupted by the openings. to act at one-third the depth of the bearing area The equivalent of reinforcement interrupted measured from the span face of the wall. Where there shall be added on all sides of~the openings. is an in-situ concrete floor continuous over the wall, c> In the area common to one column strip and one the load shall be assumed to act at the centre of the middle strip, not more than one-quarter of the wall. rebforcement in either strip shall be interrupted The resultant eccentricity of the total vertical load on by the openings. The equivalent of rein- a braced wall at any level between horizontal lateral forcement interrupted shall be added on all sides supports, shall be calculated on the assumption that of the openings. the resultant eccentricity of all the vertical loads above 4 The shear requirements of 31.6shall be satisfied. the upper support is zero. 32.2.3 Maximum Effective Height to Thickness Ratio 32 WALLS The ratio of effective height to thickness, H,.Jt shall 32.1 General not exceed 30. Reinforced concrete walls subjected to direct 32.2.4 Effective Height compression or combined flexure and direct compression should be designed in accordance with The effective height of a braced wall shall be taken as Section 5 or Annex B provided the vertical follows: reinforcement is provided in each face. Braced walls a) Where restrained against rotation at both ends subjected to only vertical compression may be designed by 61
  • IS 456 : 2000 1) floors 0.15 H, or where 2) intersecting walls or 0.75 L, V” = shear force due to design loads. similar members = t wall thickness. whichever is the lesser. d = 0.8 x L, where L, is the length of b) Where not restrained against rotation at both the wall. ends by Under no circumstances shall the nominal 1) floors 1.0 H, or shear stress 7Vw walls exceed 0.17 fck in limit state in 2) intersecting~walls or 1.0 L, method and 0.12 fckin working stress method. similar-members whichever is the lesser. 32.4.3 Design Shear Strength of Concretewhere The design shear strength of concrete in walls, H, = the unsupported height of the wall. z CW’ without shear reinforcement shall be taken as = the horizontal distance between centres below: L, of lateral restraint. a) For H, IL,+ 132.2.5 Design Axial Strength of Wall z,, = (3.0 - &/ LJ K, KThe design axial strength Puw unit length of a braced perwall in compression may be calculated from the where K, is 0.2 in limit state method and 0.13following equation: in working stress method. Puw = 0.3 (t - 1.2 e - 2e,)f,, b) For HJLw > 1 where Lesser of the values calculated from (a) t = thickness of the wall, above and from e = eccentricity of load measured at right angles to the plane of the wall determined in accordance with 32.2.2, and e a = additional eccentricity due to slen- where K, is 0.045 in limit state method and derness effect taken as H,,l2 500 t. 0.03 in working stress method, but shall be not less than K3 Jfck in any case, where K,32.3 Walls Subjected to Combined Horizontal is 0.15 in limit state method and 0.10 inand Vertical Forces working stress method.32.3.1 When horizontal forces are in the plane of the 32.4.4. Design of Shear Reinforcementwall, it may be designed for vertical forces inaccordance with 32.2 and for horizontal shear in Shear reinforcement shall be provided to carry a shearaccordance with 32.3. In plane bending may be equal to Vu - Tcw.t(0.8 LJ. In case of working stressneglected in case a horizontal cross-section of the wall method Vu is replaced by V. The strength of shearis always under compression due to combined effect reinforcement shall be calculated as per 40.4 or B-5.4of horizontal and vertical loads. with All”defined as below:32.3.2 Walls subjected to horizontal forces AN = P, (0.8 LJ tperpendicular to the wall and for which the design axialload does not exceed 0.04~“~ As, shall~be designed as where P, is determined as follows:slabs in accordance with the appropriate provisions a) For walls where H, / LwI 1, P, shall be theunder 24, where Ac is gross area of the section. lesser of the ratios of either the vertical reinforcement area or the horizontal32.4 Design for Horizontal Shear reinforcement area to the cross-sectional area32.4.1 Critical Section for Shear of wall in the respective direction.The critical section for maximum shear shall be taken b) For walls where H,l Lw> 1, P, shall be theat a distance from the base of 0.5 Lw or 0.5 H, ratio of the horizontal reinforcement area towhichever is less, the cross-sectional area of wall per vertical 32.4.2 Nominal Shear Stress metre.The nominal shear stress znu in walls shall be obtained 32.5 Minimum Requirements for Reinforcementas follows: in Walls zVw VuI t.d = The reinforcement for walls shall be provided as below: 62
  • IS 456 : 2000 the minimum ratio of vertical reinforcement to be taken as the following horizontal distances: gross concrete area shall be: a) Where supported at top and bottom risers by 1) 0.001 2 for deformed bars not larger than beams spanning parallel with the risers, the 16 mm in diameter and with a characteristic distance centre-to-centre of beams; strength of 4 15 N/mm* or greater. b) Where spanning on to the edge of a landing slab, 2) 0.001 5 for other types of bars. which spans parallel, ~withthe risers (see Fig. 3) 0.0012 for welded wire fabric not larger than 17), a distance equal to the going of the stairs 16 mm in diameter. plus at each end either half the width of the landing or one metre, whichever is smaller; and b) Vertical reinforcement shall be spaced not farther apart than three times the wall thickness c>Where the landing slab spans in the same nor 450 mm. direction as the stairs, they shall be considered as acting together to form a single slab and the cl The minimum ratio of horizontal reinforcement span determined as the distance centre-to-centre to gross concrete area shall be: of the supporting beams or walls, the going being 1) 0.002 0 for deformed bars not larger than measured horizontally. 16 mm in diameter and with a characteristic strength of 4 15 N/mm* or greater. 33.2 Distribution of Loading on Stairs 2) 0.002 5 for other types of bars. In the case ofstairs with open wells, where spans partly 3) 0.002 0 for welded wire fabric not larger crossing at right angles occur, the load on areas than 16 mm in diameter. common to any two such spans may be taken as one- 4 Horizontal reinforcement shall be spaced not half in each direction as shown in Fig. 18. Where flights farther apart than three times the wall thickness or landings are embedded into walls for a length of nor 450 mm. not less than 110 mm and are designed to span in the direction of the flight, a 150 mm strip may be deducted NOTE -The minimum reinforcement mny not slwnys be sufficient to provide adequate resistance to the effects of from the loaded area and the effective breadth of the shrinkageand tempemture. sectionincreased by75 mm for purposes of design (see Fig. 19).32.5.1 For walls having thickness more than 200 mm,the vertical and horizontal reinforcement shall 33.3 Depth of Sectionbe provided in two grids, one near each face of the The depth of section shall be taken as the minimumwall. thickness perpendicular to the soffit of the staircase.32.5.2 Vertical reinforcement need not be enclosedby transverse reinforcement as given in for 34 FOOTINGScolumn, if the vertical reinforcement is not greater 34.1 Generalthan 0.01 times the gross sectional area or~where thevertical reinforcement is not required for Footings shall be designed to sustain the applied loads,compression. moments and forces and the induced reactions and to ensure that any settlement which may occur shall be33 STAIRS as nearly uniform as possible, and the safe bearing33.1 Effective Span of Stairs capacity of the soil is not exceeded (see IS 1904).The effective span of stairs without stringer beams shall 34.1.1 In sloped or stepped footings the effective FIG. 17 EFFEC~~V E SPAN FOR STAIRS SUPPORTED AT EACHEND BY LANDINGSSPANNING PARALLELWITHTHERISERS 63
  • IS 456 : 2000 /-BEAM UPa 00 THE LOAD ON AREAS COMMON TO TWO SYSTEMS TO BE TAKEN AS ONE HALF IN EACH DIRECTION BREADTH FIG. 18 LOADING STAIRS OPW WELLS ON wrrn FIG. 19 LOADING STAIRS ON BUILT INTO WALLScross-section in compression shall be limited by the wherearea above the neutral plane, and the angle of slope or 40 = calculated maximum bearing pressure atdepth and location of steps shall be such that the design the base of the pedestal in N/mmz, andrequirements are satisfied at every section. Sloped andstepped footings that are designed as a unit shall be f-,k = characteristic strength of concrete atconstructed to assure action as a unit. 28 days in N/mmz.34.1.2 Thickness at the Edge of Footing 34.2 Moments and ForcesIn reinforced and plain concrete footings, the thickness 34.2.1 In the case of footings on piles, computationat the edge shall be not less than 150 mm for footings for moments and shears may be based on theon soils, nor less than 300 mm above the tops of piles assumption that the reaction from any pile isfor footings on piles. concentrated at the centre of the pile.34.1.3 In the case of plain concrete pedestals, the angle 34.22 For the purpose of computing stresses in footingsbetween the plane passing through the bottom edge of which support a round or octagonal concrete column orthe pedestal and the corresponding junction edge of pedestal, the face of the column or pedestal shall bethe column with pedestal and the horizontal plane taken as the side of a square inscribed within the(see Fig. 20) shall be governed by the expression: perimeter of the round or octagonal column or pedestal. 34.2.3 Bending Moment tanae0.9 lo@ A+1 The bending moment at any section shall be i f, determined by passing through the section a vertical A , 1’ --coLUMN ? // PLAIN CONCRE PEDEST 1’ / 1’ 1’ e 1L t ? t t FIG.20 64
  • IS 456 : 2000plane which extends completely across the footing, and 34.3 Tensile Reinforcementcomputing the moment of the forces acting over the The total tensile reinforcement at any section shallentire area of the footing on one side ofthe said plane. provide a moment of resistance at least equal to the34.2.3.2 The greatest bending moment to be used in bending moment on the section calculated inthe design of an isolated concrete footing which accordance with 34.2.3.supports a column, pedestal or wall, shall be the 34.3.1 Total tensile reinforcement shall be distributedmoment computed in the manner prescribed in across the corresponding resisting section as givenat sections located as follows: below: At the face of the column, pedestal or wall, for. a) In one-way reinforced footing, the-reinforcement footings supporting a concrete column, pedestal extending in each direction shall be distributed or wall; uniformly across the full width of the footing; b) Halfway between the centre-line and the edge b) In two-way reinforced square footing, the of the wall, for footings under masonry walls; reinforcement extending in each direction shall and be distributed uniformly across the full width cl Halfway between the face of the column or of the footing; and pedestal and the edge of the gussetted base, for footings under gussetted bases. cl In two-way reinforced rectangular footing, the reinforcement in the long direction shall be34.2.4 Shear and Bond distributed uniformly across the full width of the footing. For reinforcement in the short34.2.4.1 The shear strength of footings is governed by direction, a central band equal to the width ofthe more severe of the following two conditions: the footing shall be marked along the length of a) The footing acting essentially as a wide beam, the footing and portion of the reinforcement with a potential diagonal crack extending in a determined in accordance with the equation plane across the entire width; the critical section given below shall be uniformly distributed for this condition shall be assumed as a vertical across the central band: section located from the face of the column, pedestal or wall at a distance equal to the Reinforcement in central band width =- 2 effective depth of footing for footings on piles. Total reinforcement in short direction p+ 1 b) Wo-way action of the footing, with potential where /3 is the ratio of the long side to the short diagonal cracking along the surface of truncated side of the footing. The remainder of the cone or pyramid araund the concentrated load; reinforcement shall be-uniformly distributed in in this case, the footing shall be designed for the outer portions of the footing. shear in accordance with appropriate provisions specified in 31.6. 34.4 ‘Ihnsfer of Load at the Base of Column34.2.4.2 In computing the external shear or any section The compressive stress in concrete at the base of athrough a footing supported on piles, the entire reaction column or pedestal shdl be considered as beingfrom any pile of diameter DP whose centre is located transferred by bearing to the top of the supportingDP/2 or more outside the section shall be assumed as Redestal or footing. The bearing pressure on the loadedproducing shear on the section; the reaction from any area shall not exceed the permissible bearing stress inpile whose centre is located Dr/2 or more inside the direct compression multiplied by a value equal tosection shall be assumed as producing no shear on thesection, For intermediate positions of the pile centre,the portion of the pile reaction to be assumed asproducing shear on the section shall be based on d A A2 but not greater than 2; wherestraight line interpolation between full value at D,,/2outside the section and zero value at D,,/2 inside the A, = supporting area for bearing of footing, section. which in sloped or stepped footing may be taken as the area of the lower base of The critical section for checking the the largest frustum of a pyramid or cone development length in a footing shall be assumed at contained wholly within the footing and the same planes as those described for bending moment having for its upper base, the area actually in 34.2.3 and also at all other vertical planes where loaded and having side slope of one abrupt changes of section occur. If reinforcement is vertical to two horizontal; and curtailed, the anchorage requirements shall be checked in accordance with 262.3. A* = loaded area at the column base. 65
  • IS 456 : 2000 For working stress method of design the permissible diameter shall no exceed the diameter of the column bearing stress on full area of concrete shall be taken as ~bars by more than 3 mm. 0.25tk; for limit state method of design the permissible 34.4.4 Column bars of diameters larger than 36 mm, bearing stress shall be 0.45 f,. in compression only can be dowelled at the footings 34.4.1 Where the permissible bearing stress on the with bars of smaller size of the necessary area. The concrete in the supporting or supported member would dowel shall extend into the column, a distance equal be exceeded, reinforcement shall be provided for to the development length of the column bar and into developing the excess force, either by extending the the footing, a distance equal to the development length longitudinal bars into the supporting member, or by of the dowel. dowels (see 34.4.3). 34.5 Nominal Reinforcement 34.4.2 Where transfer of force is accomplished by, reinforcement, the development length of the 34.51 Minimum reinforcement and spacing shall be reinforcement shall be sufficient to transfer the as per the requirements of solid slab. compression or tension to the supporting member in 34.52 The nominal reinforcement for concrete accordance with 26.2. sections of thickness greater than 1 m shall be 34.4.3 Extended longitudinal reinforcement or dowels 360 mm* per metre length in each direction on each of at least 0.5 percent of the cross-sectional area of the face. This provision does not supersede the requirement supported column or pedestal and a minimum of four of minimum tensile reinforcement based on the depth bars shall be provided. Where dowels are used, their of the section. 66
  • IS 456 : 2000 SECTION 5 STRUCTURAL DESIGN (LIMIT STATE METHOD)35 SAFETY AND SERVICEABILITY limits of cracking would vary with the type of structureREQUIREMENTS and environment. Where specific attention is required to limit the designed crack width to a particular value,35.1 General crack width calculation may be done using formulaIn the method of design based on limit state concept, given in Annex F.the structure shall be designed~to withstand safely all The practical objective of calculating crack width isloads liable to act on it throughout its life; it shall also merely to give guidance to the designer in makingsatisfy the serviceability requirements, such as appropriate structural arrangements and in avoidinglimitations on deflection and cracking. The acceptable gross errors in design, which might result inlimit for the safety and serviceability requirements concentration and excessive width of flexural crack.before failure occurs is called a ‘limit state’. The aim The surface width of the cracks should not, in general,of design is td achieve acceptable probabilities that ~exceed 0.3 mm in members where cracking is notthe structure will not become unfit for the use for which harmful and does not have any serious adverse effectsit isintended, that is, that it will not reach a limit state. upon the preservation of reinforcing steel nor upon the351.1 All relevant limit states shall be considered in durability of the structures. In members where crackingdesign to ensure an adequate degree of safety and in the tensile zone is harmful either because they areserviceability. In general, the structure shall be exposed to the effects of the weather or continuouslydesigned on the basis of the most critical limit state exposed to moisture or in contact soil or ground water,and shall be checked for other limit states. an upper limit of 0.2 mm is suggested for the maximum35.1.2 For ensuring the above objective, the design width of cracks. For particularly aggressiveshould be based on characteristic values for material environment, such as the ‘severe’ category in Table 3,strengths and applied loads, which take into account the assessed surface width of cracks should not inthe variations in the material strengths and in the loads general, exceed 0.1 be supported. The characteristic values should bebased on statistical data if available; where such data 35.4 Other Limit Statesare not available they should be based on experience. Structures designed for unusual or special functionsThe ‘design values’ are derived from the characteristic shall comply with any relevant additional limit statevalues through the use of partial safety factors, one considered appropriate to that structure.for material strengths and the other for loads. In theabsence of special considerations these factors should 36 CHARACTERISTIC AND DESIGNhave the values given in 36 according to the material, VALUES AND PARTIAL SAFETY FACTORSthe type of loading and the limit state being 36.1 Characteristic Strength of Materialsconsidered. The term ‘characteristic strength’ means that value of35.2 Limit State of Collapse the strength of the material below which not more thanThe limit state of collapse of the structure or part of 5 percent of the test results are expected to fall. Thethe structure could be assessed from rupture of one or characteristic strength for concrete shall be inmore critical sections and from buckling due to elastic accordance with Table 2. Until the relevant Indianor plastic instability (including the effects of sway Standard Specifications for reinforcing steel arewhere appropriate) or overturning. The resistance to modified to include the concept of characteristicbending, shear, torsion and axial loads at every section strength, the characteristic value shall be assumed asshall not be less than the appropriate value at that the minimum yield stress/O.2 ~percent proof stresssection produced by the probable most unfavourable specified in the relevant Indian Standard Specifications.combination of loads an the structure using the 36.2 Characteristic Loadsappropriate partial safety factors. The term ‘characteristic load’ means that value of load 35.3 Limit States of Serviceability which has a 95 percent probability of not being exceeded during the life of the structure. Since data are not 35.3.1 Deflection available to express loads in statistical terms, for the Limiting values of deflections are given in 23.2. purpose of this standard, dead loads given in IS 875 (Part l), imposea loads given in IS 875 (Part 2), wind 35.3.2 Cracking loads given in IS 875 (Part 3), snow load as given in Cracking of concrete should not adversely affect the IS 875 (Part 4) and seismic forces given in IS 1893 appearance or durability of the structure; the acceptable shall be assumed as the characteristic loads. 67
  • IS 456 : 200036.3 Design Values 36.4.2 Partial Safety Factor y,,, for Mateiral36.3.1 Materials StrengthThe design strength of-the materials,& is given by When assessing the strength of a structureor structuralmember for the limit state of collapse, the f values of partial safety factor, us should be taken as ii=-;;- lm 1.5 for concrete and 1.15 for steel.where NOTE - 1~ values are already incorporated in the equations and tables given in this standard for limit state f = characteristic strength of the material design. (see 36.1), and When assessing the deflection, the material Ym = partial safety factor appropriate to the properties such as modulus of elasticity should be material and the limit state being taken as those associated with the characteristic considered. strength of the material.36.3.2 Loadr 37ANALYsIsThe design load, F, is given by 37.1 Analysis of Structure Fd=FYf Methods of analysis as in 22 shall be used, Thewhere material strength to be assumed shall be characteristic values in the determination of elastic ~properties,of F= characteristic load (see 36.2). and members irrespective of the limit state being Yf = partial safety factor appropriate to the considered. Redistribution of the calculated moments nature of loading and the limit state being may be made as given in 37.1.1. considered. 37.1.1. Redistribution of Moments in Continuous Beams and Frames36.3.3 Consequences of Attaining Limit State The redistribution of moments may be carried outWhere the consequences of a structure attaining a limit satisfying the following conditions:state are of a serious nature such as huge loss of life a) Equilibirumbetween the interal forces and theand disruption of the economy, higher values for yf external loads is maintained.and ym than those given under 36.4.1 and 36.4.2 may b) The ultimate moment of resistance provided atbe applied. any section of a member is not less than 7036.4 Partial Safety Factors percent of the moment at that section obtained from an elastic maximum moment diagram36.4.1 Partial Safety Factor y f for Loads covering all appropriatecombinations of loads.The values of yf given in Table 18 shall normally be c) The elastic moment at any section in a memberused. due to a particularcombination of loads shall Table 18 Values of Partial Safe@ Factor y, for Loads (Ckwe~ umf B4.3) Load Combination Limit State ef Collapse Limit stated of c Serviceability 4. DL IL WL DL IL WL (1) (2) (3) (4) (5) (6) (7) e w DL+IL 1.5 I.0 1.0 1.0 DL+WL 1.5 or 1.5 1.0 1.0 $J” DL+IL+ WL 1.2 1.0 0.8 0.8 NOTES 1 While consideringearthquakeeffects, substituteEL for WL 2 For the limit states of serviceability,the values of 7r given in this table m applicablefor shorttern effects. While assessing the long term effects due to creep the dead load and that pat of the live load likely to be permanentmay only be consided. I) This value is to be consideredwhen stability against overturning stress reversalis critical. or 68
  • IS 456 : 2000 not be reduced by more than 30 percent of the b) The maximum strain in concrete at the numerically largest moment given anywhere by outermost compression fibre is taken as 0.003 5 the elastic maximum moments diagram for the in bending. particular member, covering all appropriate cl The relationship between the compressive stress combination of loads. distribution in concrete and the strain in concrete 4 At sections where the moment capacity after may be assumed to be rectangle, trapezoid, redistribution is less than that from the elastic parabola or any other shape which results in maximum moment diagram, the following prediction of strength in substantial agreement relationship shall be satisfied: with the results of test. An acceptable stress- strain curve is given in Fig. 21. For design s+s SO.6 purposes, the compressive strength of concrete d 100 in the structure shall be assumed to be 0.67 timeswhere the characteristic strength. The partial safety X = depth of neutral axis, factor y, = 1.5 shall be applied in addition to this. d” = effective depth, and NOTE - For the stress-stin curve in Fig. 21 the design 6M = percentage reduction in moment. stress block pnrnmeters as follows (see Fig. 22): are e) In structures in which the structural frame Arenof stress block = 0.36.f,.xU provides the lateral stability, the reductions in Depth of centreof compressive force = 0.425 moment allowed by condition 37.1.1 (c) shall from the extreme fibre in compression be restricted to 10 percent for structures over 4 Where storeys in height. & = characteristic compressive strengthof concrete, nnd37.1.2 Analysis of Slabs Spanning in Two Directions zU= depthof Right Angles 4 The tensile strength of the concrete is ignored.Yield line theory or any other acceptable method e) The stresses in the reinforcement are derivedmay be used. Alternatively the provisions given in from representative stress-strain curve for theAnnex D may be followed. type of steel used. Qpical curves are given in Fig. 23. For design purposes the partial safety38 LIMIT STATE OF COLLAPSE : FLEXURE factor Ym, equal to 1.15 shall be applied.38.1 Assumptions f) The maximum strain in the tension reinforce-Design for the limit state of collapse in flexure shall ment in the section at failure shall not bebe based on the assumptions given below: less than: a) Plane sections normal to the axis remain plane after bending. where f, = characteristic strength of steel, and E, = modulus of elasticity of steel. I%67fc,, T 0.002 0.0035 STRAIN - FIG. 21 STRESS-STRAINCURVEFORCONCRETE FIG. 22 STRESSI~LOCKPARAMETERS 69
  • IS 456 : 2000 fY fy /I.15 ES 8 200000 N/mm2 23A Cold Worked Deformed Bar E, =ZOOOOO N/mm2 STRAIN - 238 STEEL BARWITH DEFINITE YIELDPOINT STRESS-STRAIN FIG. 23 REPRESENTATIVE CURVESFORREINFORCEMENT NOTE - The limiting values of the depth of neutralaxis for 38.1 (e) for flexure, the following shall be assumed: differentgradesof steel based on the assumptionsin 38.1 are. as follows: a) The maximum compressive strain in concrete f in axial compression is taken as 0.002. ‘Y *4nulld 250 0.53 b) The maximum compressive strain at the highly 415 0.48 compressed extreme fibre in concrete subjected 500 0.46 to axial compression and bending and when * The expression for obtaining the moments of resistance for there is no tension on the section shall be 0.003 5 rectangularnnd T-Sections, based on the assumptionsof 38.1, are minus 0.75 times the strain at the least given in Annex G. compressed extreme fibre. 39 LIMIT STATE OF COLLAPSE : COMPRESSION 39.2 Minimurdccentricity 39.1 Assumptions All members in compression shall be designed for the In addition to the assumptions given in 38.1 (a) to minimum eccentricity in accordance with25.4. Where 70
  • IS 456 : 2000calculated eccentricity is larger, the minimum 39.6 Members Subjected to Combined Axial Loadeccentricity should be ignored. and Biaxial Bending39.3 Short Axially Loaded Members in The resistance of a member subjected to axial forceCompression and biaxial bending shall be obtained on the basis of assumptions given in 39.1 and 39.2 with neutral axisThe member shall be designed by considering the so chosen as to satisfy the equilibrium of load andassumptions given in 39.1 and the minimum moments about two axes. Alternatively such memberseccentricity. When the minimum eccentricity as may be designed by the following equation:per 25.4 does not exceed 0.05 times the lateraldimension, the members may be designed by thefollowing equation: P” = 0.4 fd .Ac + 0.674 .A= wherewhere MUX, MU, = moments about x and y axes ?J” = axial load on the member, due to design loads, f& = characteristic compressive strength of the KX,, M”Yl = maximum uniaxial moment concrete, capacity for an axial load of P,, bending about x and y axes AC = Area of concrete, respectively, and f, = characteristic strength of the compression 01” related to P;/Puz is reinforcement, and where Puz= 0.45 f, . AC+ 0.75&A, As = area of longitudinal reinforcement for For values of P,lp., = 0.2 to 0.8, the values of cs,,vary columns. linearly from 1.Oto 2.0. For values less than 0.2, a, is 1.O;for values greater than 0.8, an 2.0. is39.4 Compression Members with HelicalReinforcement 39.7 Slender Compression MembersThe strength of compression members with helical The design of slender compression membersreinforcement satisfying the requirement of 39.4.1 shall (see 25.1.1) shall be based on the forces and thebe taken as 1.05 times the strength of similar member moments determined from an analysis of the structure,with lateral ties. including the effect of deflections on moments and39.4.1 The ratio of the volume of helical reinforcement forces. When the effect of deflections are not takento the volume of the core shall not be less than into account in the analysis, additional moment given in 39.7.1 shall be taken into account in the appropriate direction. Al = gross area of the section, 39.7.1 The additional moments M, and My, shall be calculated by the following formulae: A, = area of the core of the helically reinforced cc+Iumn measured to the outside diameter of the helix, Ma% & = characteristic compressive strength of the concrete, and & = characteristic strength of the helical reinforcement but not exceeding where 415 N/mm*. P” = axial load on the member,39.5 Members Subjected to Combined Axial 1, = effective length in respect of the majorLoad and Uniaxial Bending axis, A member subjected to axial force and uniaxiaMxmding 1 = effective length in respect ofthe minor axis, shall be designed on the basis of 39.1 and 39.2. o”= depth of the cross-section at right angles NOTE-The design of membersubjectto canbii axial load to the major axis, and and uniaxial bending will involve lengthy calculation by trial and error.In order to overcome these difficulties interaction b = width of the member. diugmmsmay~be used. These have been prepared published and by BIS in ‘SP : 16 Design uids ~forreinforced concrete to For design of section, 39.5 or 39.6 as appropriate shall IS 456’. apply* 71
  • IS 456 : 2000 NOTES of the beam. 1 A column may be consideredbracedin a givenplane lateral if The negative sign in the formula applies when the stability to the structureas a whole is providedby walls or bracing or buttressingdesigned to resist all latexalforces in bending moment iU”increases numerically in the same that plane. It should otherwise be considered unbmced. as direction as the effective depth d increases, and the 2 In the case of a braced column without any transverseloads positive sign when the moment decreases numerically occurring in its height, the additional moment shall be added in this direction. to an initial moment equal to sum of 0.4 My, and 0.6 MB, where Mu,is the largerend moment and Mu, is the smaller 40.2 Design Shear Strength of Concrete end moment (assumed negative if the column is bent in double curvature). In no case shall the initial moment be less than 40.2.1 The design shear strength of concrete in beams 0.4 Mu,nor the total moment including the initial moment be without shear reinforcement is given in Table 19. less than Mm,.For unbraced columns, the additional moment shall be added to the end moments. For solid slabs, the design shear strength for 3 Unbraced compression members, at any given level or storey, concrete shall be zck, wheie k has the values given subject to lateral load are usually constrained to deflect below: equally. In suth cases slenderness ratio for each column may be taken as the average for all columns acting in the same OverallDepth 300or 275 250 225 200 175 15Oor direction. ofS6ab,mm more less39.7.1.1 The values given by equation 39.7.1 may be k 1.00 1.05 1.10 I.15 1.20 1.25 1.30multiplied by the following factor: NOTE -This provision shall not apply to flat slabs for which 31.6 shall apply. k =p,,-P,<l pu, 8 - 40.2.2 Shear Strength of Members under Axial Compressionwhere P* = axial load on compression member, For members subjected to axial compression P,, the design shear strength of concrete, given in Table 19, P*z = as defined in 39.6, and shall be multiplied by the following factor : _Ph = axial load corresponding to the condition of maximum compressive strain of 6 = 1+ 2 but-not exceeding 1.5 0.003 5 in concrete and tensile strain of 0.002 in outer most layer of tension steel. where40 LIMIT STATE OF COLLAPSE : SHEAR P” = axial compressive force in Newtons, = gross area of the concrete section in mm2,40.1 Nominal Shear Stress As andThe nominal shear stress in beams of uniform depthshall be obtained by the following equation: f,l: = characteristic compressive strength of concrete. 2, = v, 40.2.3 WithShear Reinforcement ‘d Under no circumstances, even with shear where reinforcement, shall the nominal shear stress in beams vu = shear force due to design loads; z, execed z,_ given in Table 20. b = breadth of the member, which for flanged For solid slabs, the nominal shear stress section shall be taken as the breadth of shall not exceed half the appropriate values given in the web, bw; and Table 20. d = effective depth. 40.3 Minimum Shear Reinforcement 40.1.1 Beams of Varying Depth When z, is less than z, given in Table 19, minimum In the case of beams of varying depth the equation shear reinforcement shall -be provided in accordance shall be modified as: with v,++tanp 40.4 Design of Shear Reinforcement z, = When 7t, ~exceeds ‘5, given in Table 19, shear bd reinforcement shall be provided in any of the following where forms: z “, VU,b and d are the same as in 40.1, a) Vertical stirrups, M,, = bending moment at the section, and b) Bent-up bars along with stirrups, and p = angle between the top and the bottom edges 72
  • I!3456:2000 Table 19 Design Shear Strength of Concrete, 5, , N/mm2 (Clauses,40.3,40.4, and41.4.3) ConcBteGrade , M 15 M20 M25 M30 M35 M4Oandabove (1) (2) (3) (4) (5) (6) (7) S0.H 0.28 0.28 0.29 0.29 0.29 0.30 0.25 0.35 0.36 0.36 0.37 0.37 0.38 0.50 0.46 0.48 0.49 0.50 0.50 0.51 0.75 0.54 0.56 0.57 0.59 0.59 0.60 1.00 0.60 0.62 0.64 0.66 0.67 0.68 1.25 0.64 0.67 0.70 0.71 ~0.73 0.74 1.50 0.68 0.72 0.74 0.76 0.78 0.79 1.75 0.71 0.75 0.78 0.80 0.82 0.84 2.00 0.71 0.79 0.82 0.84 0.86 0.88 2.25 0.71 0.81 0.85 0.88 0.90 0.92 2.50 0.71 0.82 0.88 0.91 0193 0.95 2.75 0.7 1 0.82 0.90 0.94 O.% 0.98 3.00 0.71 0.82 0.92 0.96 0.99 l.Oj and above NOTE - The tern A, is the area of longitudii temioa reinforcement which continues at least one effective depth beyond the section being considered except at support whete the full ama of tension reinfotrement may be used provided the detailing conforms to 26.23 and X.2.3 able 20 Maximum Shear Stress, ITS _ , N/m& (C&~es40.,40.5.1Md41.3.1) Concrete M 15 MU) M 25 M30 M 35 M40 ~Grade aad aboveT,,,Wmm’ 2.5 2.8 3.1 3.5 3.7 4.0 c) Inclined stirrups, V, = 0.874 A, sin aWhere bent-up bars are provided, their contribution wheretowards shear resistance shall not be more than half total cross-sectional area of stirrup legs AS” =that of the total shear reinforcement. or bent-up bars within a distance sV.Shear reinforcement shall be provided to carry a shear sY = spacing of the stirrups or bent-up barsequal to Vu- z, bd The strength of shear reinforce- along the length of the member,ment Vu, shall be calculated as below: 0, = nominal shear stress, a) For vertical stirrups: z, = design shear strength of the concrete, 0.87 fy q,d b = breadth of the member which for v“I = flanged beams, shall be taken as the S” breadth of the web by, b) For inclined stirrups or a series of bars bent-up characteristic strength of the stirrup or f, = at different cross-sections: bent-up reinforcement which shall not be taken greater than 415 N/mmz, 0.8.7 fybvd vUS= (sin 01+ cos a) a = angle between the inclined stirrup or S” bent- up bar and the axis of the member, c) For single bar or single group of parallel bars, not less than 45”, and all bent-up at the same cross-section: d = effective depth. 73
  • IS 456 : 2000 NOTES is given by: 1 Wheremore thaa one type of shearreinforcement used is to reinforcethe same portionof the beam, the total shear As=avb(zV-2d’tc/aV)10.87fy20.4a,b/0.87fy resistanceshall be computedas the sumof the resistance for the various types separately. This reinforcement should be provided within the middle 2 The areaof the stim~psshallnotbe less thanthe miniium three quarters of a,, where aVis less than d, horizontal specified in 265.1.6. shear reinforcement will be effective than vertical.40.5 Enhanced Shear Strength of Sections Close 40.5.3 Enhanced Shear Strength Near Supportsto supports (Simplified Approach)40.5.1 General The procedure given in 40.51 and 40.5.2 may beused for all beams. However for beams carrying generallyShear failure at sections of beams and cantilevers uniform load or where the principal load is locatedwithout shear reinforcement will normally occur on farther than 26 from the face of support, the shearplane inclined at an angle 30” to the horizontal. If the stress maybe calculated at a section a distance d fromangle of failure plane is forced to be inclined more the face of support. The value of 2, is calculated insteeply than this [because the section considered accordance with Table 19 and appropriate shear(X - X) in Fig. 24 is close to a support or for other reinforcement is provided at sections closer to thereasons], the shear force~required to produce failureis support, no furthercheck for shear at such sections isincreased. required.The enhancement of shear strength may be takeninto account in the design of sections near a support 41 LIMlT STATE OF COLLAPSE : TORSIONby increasing design shear strength of concrete to 41.1 General 2d z, /a, provided that design shear stress at the faceof the support remains less than the values given in In structures, where torsion is required to maintainTable 20. Account may be taken of the enhancement equilibrium, members shall be designed for torsion inin any situation where the section considered is closer accordancewith 41.2,41.3 and41A. However, for such indeterminate structureswheretorsioncan be eliminatedto the face of a support or concentrated load than twice by releasingredundantrestraints,no specific design forthe effective depth, d. To be effective, tension torsion is necessary, provided torsional stiffness isreinforcement should extend on each side of the point neglected in the calculationof internalforces.Adequatewhere it is intersected by a possible failure plane for a controlof any torsionalcrackingis providedby the sheardistance at least equal to the,effective depth, or beprovided with an equiv.dent anchorage. reinforcementas per 40. NOTE -The approachto desip in this clause is as follows:40.52 Shear Reinforcement for Sections Close to Torsionalreinforcementis not calculated separately from thatsupports requiredfor beading and shear. Instead the total longitudinal reinforcementis determinedfor a fictitious bending momentIf shear reinforcement is required, the total area of this which is a function of actual bending moment and torsion; X NOTE-The shear causing failureis that acting on section X-X. FIG.24 SHIM FAILURE SIJFWI~~~ NEAR 74
  • Is456:2000 similarly web reinforcement is determined for a fictitious shear where which is a function of actual shear and torsion. x is the torsional moment, D is the overall depth41.1.1 The design rules laid down in 41.3 and 41.4 of the beam and b is the breadth of the beam.shall apply to beams of solid rectangular cross-section.However, these clauses may also be applied to flanged If the numerical value of M, as definedbeams, by substituting bwfor 6 in which case they are in 41.4.2 exceeds the numerical value of the momentgenerally conservative; therefore specialist literature Mu, longitudinal reinforcement shall be provided onmay be referred to. the flexural compression face, such that the beam can also withstand an equivalent Me* given by41.2 Critical Section Me2 = Mt - Mu, the moment M, being taken as actingSections located less than a distance d, from the face in the opposite sense to the moment M,.of the support may be designed for the same torsion ascomputed at a distance d, where d is the effective depth. 41.4.3 Transverse Reinforcement Two legged closed hoops enclosing the corner41.3 Shear and Torsion longitudinal bars shall have anarea of cross-section41.3.1 Equivalent Shear Aly, given byEquivalent shear, V,, shall be calculated from the q, = TUG v, svformula: b, dI (0.87 &,) + 2.5d, (0.87&J ’ v, =V, + 1.6 $ but the total transverse reinforcement shall not be lesswhere -Z,)b.S, (Ge Y = equivalent shear, 0.87 fy Vu = shear, q = torsional moment, and where b = breadth of beam. Tu = torsional moment,The equivalent nominal shear stress, 2, in this case V” = shear force,shall be calculated as given in 40.1, except for S” = spacing of the stirrup reinforcement,substituting Vuby V,. The values of zvcshall not exceedthe values of z, mur given in Table 20. b, = centre-to-centre distance between corner bars in the direction of the width,41.3.2 If the equivalent nominal shear stress, zvedoesnot exceed zc given in ‘Iable 19, minimum shear d, = centre-to-centre distance between comerreinforcement shall be provided as per bars,41.3.3 If zVeexceeds zc given in Table 19, both b = breadth of the member,longitudinal and transverse reinforcement shall beprovided in accordance with 41.4. f) = characteristic strength of the stirrup reinforcement,41.4 Reinforcement in Members Subjected to zw = equivalent shear stress as specified inTorsion 41.3.1, and41.4.1 Reinforcement for torsion, when required, shall fc = shear strength of the concrete as per Tableconsist of longitudinal and transverse reinforcement. Longitudinal Reinforcement 42 LIMIT STATE OF SERVICEABILITY:The longitudinal reinforcement shall be designed to DEFLECTIONresist an equivalent bending moment, M,,, given by 42.1 Flexural Members Me,=M,,+M, In all normal cases, the deflection of a flexural member where will not be excessive if the ratio of its span to its Mu = bending moment at the cross-section, and effective depth is not greater than appropriate ratios given in 23.2.1. When deflections are calculated MI = T, ($!+! . according to Annex C, they shall not exceed the permissible values given in .23.2. 75
  • 1s 456 : 200043 LIMIT STATE OF SERVICEABILITY: 43.2 Compression MembersCRACKING Cracks due to bending in a compression member43.1 Flexural Members subjected to a design axial load greater than 0.2fc, AC, wheref, is the characteristic compressive strength ofIn general, compliance with the spacing requirements concrete and AEis the area of the gross section of theof reinforcement given in 26.3.2 should be sufficient member, need not be checked. A mumber subjected toto control flexural cracking. If greater spacing are lesser load than 0.2fckAI: may be consideredrequired, the expected crack width should be checked as flexural member for the purpose of crack controlby formula given in Annex F. (see 43.1). 7G
  • ANNEX A (Clal&&? 2) LIST OF REFERRED INDIAN STANDARDS IS No. ISNo. ‘litle269 : 1989 Specification for ordinary 1642 : 1989 Code of practice for fire safety Portland cement, 33 grade (fourth of buildings (general) : DeWs of revision) construction (first revision)383 : 1970 Specification for coarse and fine 1786 : 1985 Specification for high strength aggregates from natural sources &formed steel bars and wires for for concrete (second revision) concrete reinforcement (third432 (Part 1) : Specification for mild steel and revision) 1982 medium tensile steel bars and 1791 : 1968 Specification for batch type hard-drawn steel wire for concrete mixers (second revision) concrete reinforcement: Part 1 1893 : 1984 Criteria for earthquake resistant Mild steel and medium tensile design of structures (fourth steel bars (third revision) revision)455 : 1989 Specification for Portland slag 1904 : 1986 Code of practice for &sign and cement yburth revision) construction of foundations in516: 1959 Method of test for strength of soils : General requirements concrete (thin-iFevision)875 Code of practice for design loads 2062 : 1992 Steel for general structural (other than earthquake) for purposes (fourth revision) buildings and structures : 2386 (Part 3) : Methods of test for aggregates for (Part 1) : 1987 Dead loads - Unit weights of 1963 concrete : Part 3 Specific gravity, building material and stored density, voids, absorption and materials (second revision) bulking (Part 2) : 1987 Imposed loads (second revision) 2502 : 1963 Code of practice for bending and (Part 3) : 1987 Wind loads (second revision) fixing of bars for concrete reinforcement (Part 4) : 1987 Snow loads (second revision) 2505 : 1980 Concrete vibrators -Immersion (Part 5) : 1987 Special loads and load combinations (second revision) type - General requirements 2506 : 1985 General requirements for screed 1199 : 1959 Methods of sampling and board concrete vibrators (first analysis of concrete revision) 1343 : 1980 Code of practice for prestressed 2514 : 1963 Specification for concrete concrete (first revision) vibrating tables 1489 Specification for Portland 2751 : 1979 Recommended practice for pozzolana cement : welding of mild steel plain and (Part 1) : 1991 Ply ash based (third revision) deformed bars for reinforced (Part 2) : 1991 Calcined clay based (third construction (first revision) revision) Methods of sampling and test 1566 : 1982 Specification for hard-drawn (physical and chemical) for water steel wire fabric for concrete and waste water : reinforcement (second revision) (Part 17) : 1984 Non-filterable residue (total 1641 : 1988 Code of practice for fire safety suspended solids) (first revision) of buildings (general): General (Part 18) : 1984 Volatile and fixed residue (total principles of fire grading and filterable and non-filterable) (first classification yirst revision) revision) 7‘7
  • IS 456 : 2000 IS No. Title IS No. Me (Part 22) : 1986 Acidity (first revision) (Part 3) : 1972 Concrete reinforcement (Part 23) : 1986 Alkalinity (first revision) (Part 4) : 1972 Types of concrete (Part 24) : 1986 Sulphates (first revision) (Part 5) : 1972 Formwork for concrete (Part 32) : 1988 Chloride (first revision) (Part 6) : 1972 Equipment, tool and plant3414: 1968 Code of practice for design and (Part 7) : 1973 Mixing, laying, compaction, installation of joints in buildings curing and other construction aspect3812 : 1981 Specification for fly ash for use as pozzolana and admixture (first (Part 8) : 1973 Properties of concrete revision) (Part 9) : 1973 Structural aspects3951 (Part 1) : Specification for hollow clay tiles (Part 10) : 1973 Tests and testing apparatus 1975 for floors and roofs : Part 1 Filler type (first revision) (Part 11) : 1973 Prestressed concrete (Part 12) : 1973 Miscellaneous4031(Part 5) : Methods of physical tests for 1988 hydraulic cement : Part 5 6909 : 1990 Specification for supersulphated Determination of initial and final cement setting times yirst revision) 7861 Code of practice for extreme4082 : 1996 Recommendations on stacking weather concreting : and storage of construction (Part 1) : 1975 Recommended practice for hot materials and components at site weather concreting (second revision) (Part 2) : 1975 Recommended practice for cold4326 : 1993 Code of practice for earthquake weather concreting resistant design and construction of buildings (second revision) 8041 : 1990 Specification for rapid hardening Portland cement (second revision)4656 : 1968 Specification for form vibrators for concrete 8043: 1991 Specification for hydrophobic Portland cement (second revision)4845 : 1968 Definitions and terminology relating to hydraulic cement 8112 : 1989 Specification for 43 grade ordinary Portland cement (first4925 : 1968 Specification for concrete revision) batching and mixing plant 9013 : 1978 Method of making, curing4926 : 1976 Specification for ready-mixed and determining compressive concrete (second revision) strength of accelerated cured5816 : 1999 Method of test for splitting concrete test specimens tensile strength of concrete 9103: 1999 Specification for admixtures for (first revision) concrete (first revision)606 I Code of practice for construction Recommendations for welding 9417 : 1989 of floor and roof with joists and cold worked bars for reinforced filler blocks : concrete construction (first (Part 1) : 1971 With hollow concrete filler revision) blocks 11817 : 1986 Classification of joints in (Part 2) : 1971 With hollow clay filler blocks buildings for accommodation of (first revision) dimensional deviations during 6452 : 1989 Specification for high alumina construction cement for structural use 12089 : 1987 Specification forgranulated slag Glossary of terms relating to for manufacture of Portland slag 646 1 cement: cement 12119 : 1987 General requirements for pan (Part 1) : 1972 Concrete aggregates mixers for concrete (Part 2) : 1972 Materials 78
  • IS 456 : 2000 IS No. Title IS No. Title12269 : 1987 Specification for 53 grade (Part 1) : 1992 Ultrasonic pulse velocity ordinary Portland cement (Part 2) : 1992 Rebound hammer12330: 1988 Specification for sulphate 13920 : 1993 Code of practice for ductile resisting Portland cement detailing of reinforced concrete12600 : 1989 Specification for low heat structures subjected to seesmic Portland cement forces13311 Methods of non-destructive 14687 : 1999 Guidelines for falsework for testing of concrete : concrete structures 79
  • IS 456 : 2000 ANNEX B (Clauses 18.2.2,22.3.1,22.7,26.2.1 and 32.1) STRUCTURAL DESIGN (WORKING STRESS METHOD)B-l GENERAL c) The stress-strain relationship of steel and concrete, under working loads, is a straight line.B- 1 .l General Design Requirements 280The general design requirements -of Section 3 shall d) The modular ratio m has the value -apply to this Annex. 30&c where cCchc permissible compressive stress due isB-l.2 Redistribution of Momenta to bending in~concrete in N/mm2 as specified in Table 21.Except where the simplified analysis using coefficients(see 22.5) is used, the moments over the supports for NOTE- The expressiongiven for m partially takes into account long-term effects such as creep. TherefoE this many assumed arrangement of loading, including the is not the same us the modular mtio derived bused on thedead load moments may each be increased or decreased value of E, given in not more than 15 percent, provided that thesemodified moments over the supports are used for the B-2 PERMISSIBLE STRESSEScalculation of the corresponding moments in the spans. B-2.1 Permissible Stresses in ConcreteB-l.3 Assumptions for Design of Members Permissible stresses for the various grades of concrete shall be taken as those given in Tables 21 and 23.In the methods based on elastic theory, the following NOTE - For increase in strength with age 6.2.1 shall beassumptions shall be made: applicable. The values of permissible stress shall be obtained by interpolation~between the grades of concrete.. a) At any cross-section, plane sections before bending remain plain after bending. B-2.1.1 Direct Tension b) All tensile stresses are taken up by reinforcement For members in direct tension, when full tension is and none by concrete, except as otherwise taken by the reinforcement alone, the tensile stress shall specifically permitted. be not greater than the values given below: Grcrde of M 10 M IS M 20 M 25 M 30 M 35 M 40 M45 M 50 Concrerc Tensile stress, 1.2 2.0 2.8 3.2 3.6 4.0 4.4 4.8 5.2 N/mm2 B-2.2 Permissible Stresses in Steel ReinforcementThe tensile stress shall be calculated as F, Permissible stresses in steel reinforcement shall not AC +m%, exceed the values specified in Table 22. B-2.2.1 In flexural members the value of (T, given in Table 22 is applicable at the centroid of the tensile F, = total tension on the member minus pre- reinforeement subject to the condition that when more tension in steel, if any, before concreting; than one layer of tensile reinforcement is provided, Ac = cross-sectional area of concrete excluding the stress at the centroid of the outermost layer shall any finishing material and reinforcing not exceed by more than 10 percent the value given in steel; Table 22. m = modular ratio; and B-2.3 Increase in~permissible Stresses 4 = cross-sectional area of reinforcing steel Where stresses due to wind (or earthquake) temperature in tension. and shrinkage effects are combined with those due to dead, live and impact load, the stresses specified inB-2.1.2 Bond Stress for Deformed Bars Tables 21,22 and 23 may be exceeded upto a limit ofIn the case of deformed bars conforming to IS 1786, 333 percent. Wind and seismic forces need not bethe bond stresses given in Table 21 may be increasedby 60 percent. considered as acting simultaneously. 80
  • Table 21 Permissible Stresses in Concrete IS 456: 2000 (Clauses B-1.3, B-2.1, B-2.1.2, B-2.3 &B-4.2) All values in N/mm’.Grade of Permissible Stress in Compression . Permissible StressConcrete in Bond (Average) for Bending Direct Plain Bars in Tension(1) (2) (3) (4) QCk 0, ‘NM 10 3.0 2.5 -M IS 5.0 4.0 0.6M 20 7.0 5.0 0.XM 25 a.5 6.0 0.9M 30 10.0 8.0 1.0M 35 11.5 9.0 1.1M 40 13.0 10.0 1.2M45 14.5 11.0 1.3M SO 16.0 12.0 1.4 NOTES ,. 1 The values of permissible shear stress in concrete are given in Table 23. 2 The bond stress given in co1 4 shall be increased by 25 percent for bars in compression.B-3 PERMISSIBLE LOADS IN COMPRESSION multiplication of the appropriate maximum permissibleMEMBERS stress as specified under B-2.1 and B-2.2 by theB-3.1 Pedestals and Short Columns with Lateral coefficient C, given by the following formula:Ties c, = 1.25 -lefThe axial load P permissible on a pedestal or short 486column reinforced with longitudinal bars and lateral whereties shall not exceed that given by the following cr = reduction coefficient;equation : le, = effective length of column; andwhere b = least lateral dimension of column; for permissible stress in concrete in direct column with helical reinforcement, b is o,, = compression, the diameter of the core. cross-sectional area of concrete For more~exact calculations, the maximum permissible Ac = excluding any finishing material and stresses in a reinforced concrete column or part thereof reinforcing steel, having a ratio of effective column length to least lateral radius of gyration above 40 shall not exceed those permissible compressive stress for which result from the multiplication of the appropriate column bars, and maximum permissible,stresses specified under B-2.1 ASc= cross-sectional area of the longitudinal and B-2.2 by the coefficient C, given by the following steel. formula: NOTE -The minimum eccentricity mentioned in 25.4 may be deemed to be incorporated in the above equation. C,=l.25 -I,f laOi,,B-3.2 Short Columns with Helical Reinforcement where i,,,, is the least radius of gyration.The permissible load for columns with helicalreinforcement satisfying the requirement of 39.4.1 shall B-3.4 Composite Cohunnsbe 1.05 times the permissible load for similar member a) Allowable load - The allowable axitil load Pwith lateral ties or rings.. on a composite column consisting of structuralB-3.3 Long Columns steel or cast-iron column thoroughly encased in concrete reinforced with both Jongitudinal and The maximum permissible stress in a reinforced spiral reinforcement, shall not exceed that given concrete column or part thereof having a ratio of by the following formula: effective column length to least lateral dimension above 12 shall not exceed that which results from the 81
  • IS 456 : 2000 Table 22 Permissible Stresses in Steel Reinforcement (ClausesB-2.2,B-2.2.1,B-2.3and B-4.2)Sl lLpe of Stress in Steel Permissible Stresses in N/mmNo. Reinforcement - - Mild Steel Bars Medium Tensile High Yield Strength Conforming to Steel Conform- Deformed Bars Con- Grade 1 of ing to IS 432 forming to IS 1786 IS 432 (Part 1) (Part 1) (Grade Fe 415)(1) (3) (4) (5)i) Tension ( a, or CT,) a) Up to and including 140 Half the guaranteed 230 20 mm yield stress subject to a maximum of 190 b) Over 20 mm 130 230ii) Compression in column 130 130 190 bars ( q)iii) Compression in bars in a The calculated compressive stress in the surrounding concrete multiplied by 1.5 times beam or slab when the com- the modular ratio or a= whichever is lower pressive resistance of the concrete is taken into accountiv) Compression in bars in a beam or slab where the compressive resistance of the concrete is not taken into account: a) Up to and including Half the guaranteed 190 2omm yield stress subject I to a maximum of 190 b) Over 20 mm 190 NOTES 1 For high yield strength deformed bars of Grade Fe 500 the permissible stress in direct tension and flexural tension shall be 0.55,fy. The permissible stresses for shear and compression reinforcement shall be ils for Grade Fe 415. 2 For welded wire fabric conforming to IS 1566, the permissible value in tension 0, is 230 N/mm*. 3 For the purpose of this standard, the yield stress of steels for which there is no clearly defined yield point should be taken to be 0.2 percent proof stress. 4 When mild steel conforming to Grade 11of IS 432 (Part 1) is used, the permissible stresses shall be 90 percent of the permissible stresses in co13, or if the design detaikhave already been worked out on the basis of mild steel conforming to Grade 1 of IS 432 (Part I); the area of reinforcement shall increased 10 percent that required for-Grade 1 steel. be by of 20 percent of the gross area of the column. If a permissible stress in concrete in. direct hollow metal core is used, it shall be filled with compression; concrete. The amount of longitudinal and spiral net area of concrete section; which is reinforcement and the requirements as to spacing equal to the gross area of the concrete of bars, details of splices and thickness of section -AS -Am; protective shell outside the spiral, shall conform permissible compressive stress for to require- ments of 26.5.3. A clearance of at column bars; least 75 mm shall be maintained between the cross-sectional area of longitudinal bar spiral and the metal core at all points, except reinforcement; that when the core consists of a structural steel allowable unit stress in metal core, ndt to H-column, the minimum clearance may be exceed 125 N/mm* for a steel core, or reduced to 50 mm. 70 N/mm* for a cast iron core; and c) Splices and connections of metal cores - Metal the cross-sectional area of the steel or cast cores in composite columns shall be accurately iron core. milled at splices and positive provisions shall b) Metal core and reinforcement - The cross- be made for alignment of one core above sectional area of the metal core shall notexceed another. At the column base, provisions shall be 82
  • IS 456: 2000 made to transfer the load to the footing at safe b) The resultant tension in concrete is not greater unit stresses in accordance with 34. The base of than 35 percent and 25 percent of the resultant the metal section shall be designed to transfer compression for biaxial and uniaxial bending the load from the entire composite columns to respectively, or does not exceed three-fourths, the footing, or it may be designed to transfer the 7 day modulus of rupture of concrete. the load from the metal section only, provided it is placed in the pier or pedestal as to leave NOTES ample section of concrete above the base for the P transfer of load from the reinforced concrete 1 %,4 = A, +lSmA, for columns with ties where P. A, and section of the column by means of bond on the A_ defined in B-3.1 and m-is the modularratio. vertical reinforcement and by direct M compression on the concrete, Transfer of loads 2 %W* = y where M equals the moment and Z equals to the metal core shall be provided for by the modulusof section. In the case.of sections subjectto moments use of bearing members, such as billets, brackets in two directions,the stress shall be calculatedseparatelyand or othir positive connections, these shall be added algebraically. provided at the top of the metal core and at intermediate floor levels where required. The B-4.2 Design Based on Cracked Section column as a whole shall satisfy the requirements If the requirements specified in B-4.1 are not satisfied, of formula given under (a) at any point; in -the stresses in concrete and steel shall be calculated addition to this, the reinforced concrete portion by the theory of cracked section in which the tensile shall be designed to carry, according to B-3.1 resistance of concrete is ignored. If the calculated or B-3.2 as the case may be, all floor loads stresses are within the permissible stress specified in brought into the column at levels between the Tables 21,22 and 23 the section may be assumed to be metal brackets or connections. In applying the safe. formulae under B-3.1 or B-3.2 the gross area of NOTE - The maximum saess in concrete and steel may be column shall be taken to be the area of the foundfromtables andchtis based on the crackedsection theory concrete section outside the metal core, and the or directlyby determining no-stressline which shouldsatisfy the allowable load on the reinforced concrete section the following requirements: shall be further limited to 0.28 fck times gross The direct load should be equal to the algebraicsum of sectional area of the column. the forces on concreteand steel, d) Allowable had on Metal Core Only - The The moment of the external loads about any reference line should be equal to the algebraicsum of the moment metal core of composite columns shall be of the forces in conc=te (ignoring the tensile force in designed to carry safely any construction or concrete)and steel about the same line, and other loads to be placed upon them prior to their The moment of the external loads about any other encasement in concrete. referencelines should beequal to the algebraic sum of the momentof the forcesin concrete(ignoringthe tensileB-4 MEMBERS SUBJECTED TO COMBINED force in concrete)and steel aboutthe same line.AXIAL LOAD AND BENDING B4.3 Members Subjected to Combined DirectB-4.1 Design Based on Untracked Section toad and FlexureA member subjected to axial load and bending (due toeccentricity of load, monolithic construction, lateral Members subjected to combined direct load and flexureforces, etc) shall be considered safe provided the and shall be designed by limit state method ti in 39.5following conditions are satisfied: after applying appropriate load factors as given in Table 18. B-5 SHEAR crcc CT cbcwhere B&l Nominal Shear Stress o‘..,c;ll = calculated direct compressive stress The nominal shear stress 5 in beams or slabs of in concrete, uniform depth shall be calculated by the following permissible axial compressive stress equation: in~concrete, calculated bending compressive z, 2 bd stress in concrete, and where permissible bending compressive stress in concrete. V = shear force due to design loads, 83
  • IS 456 : 2000 b = breadthof the member,which for flanged B- For solid slabs the permissible shear stress sections shall be taken as the breadth of in concrete shall be k’r, where k has the value given the web, and below: d = effective depth. Ovemlldepth3CMlar 275 250 225 200 175 15Oa of slab, mm more less B-5.1.1 Beams of Varying Depth k 1.00 1.05 1.10 1.15 1.20 1.25 1.30 In the case of beams of varying depth, the equation NOTE -This does not apply to flat slab for which 31.6 shall shall be modified as: a@ly. B-5.2.2 Shear Strength of Members Under Axial v * MtanP Compression 7” = d bd For members subjected to axial compression P, the permissible shear stress in concrete tc given where in Table 23, shall be multiplied by the following zy, V, b and d are the same as in B-5.1, factor: M = bending moment at the section, and 6=1+5p* but not exceeding 1.5 As fck p = angle between the top and the bottom edges of the beam. where P = axial compressive force in N, The negative sign in the formula applies when the Al = gross area of the concrete section id mm2, bending moment M increases numerically in the same and direction as the effective depth d increases, and the characteristic compressive strength of f, = positive sign when the moment decreases numerically concrete. in this direction. B-5.2.3 WithShear Reinforcement B-5.2 Design Shear Strength ofConcrete When shear reinforcement is provided the nominal1 B-5.2.1 The permissible shear stress in concrete in shear stress 7, in beams shall not exceed 7, _ given in beams without shear reinforcement is given in Table 23. Table 24. Table 23 Permissible Shear Stress in Concrete (Clauses B-2.1, B-2.3, B-4.2, B-5.2.1,B-5.2.2,B-5.3,B-5.4, B-5.5.1,B.5.5.3,B-6.?.2.B-6.3.3 B-6.4.3and Table 21) and 1002 Permissible Shear Stress in Concrete, T@,N/mm’ i Grade of Concrete M 15 M20 M 25 M 30 M 35 M40 and above (1) (2) (3) (4) (5) (6) (7) < 0.15 0.18 0.18 0.19 0.20 0.20 0.20 025 0.22 0.22 0.23 0.23 0.23 0.23 0.50 0.29 0.30 0.31 0.31 0.31 0.32 0.75 0.34 0.35 0.36 0.37 0.37 0.38 1.00 0.37 0.39 0.40 0.41 0.42 0.42 1.25 0.40 0.42 0.44 0.45 0.45 0.46 1so 0.42 0.45 : 0.46 0.48 0.49 0.49 1.75 0.44 0.47. 0.49 0.50 0.52 0.52 2.00 0.44 0.49 0.51 0.53 0.54 0.55 2.25 0.44 0.51 0.53 0.55 0.56 0.57 2.50 0.44 0.51 0.55 0.57 0.58 0.60 2.75 0.44 0.51 0.56 0.58 0.60 0.62 3.00 and 0.44 0.51 0.57 . 0.60 0.62 0.63 above NOTE - ASis that am of longitudinal tension reinforcement which continues at least one effective depthbeyond the section being considered except at suppotis where the full areaof tension reinforcementmay be used provided% detailiig confom to 26.23 and 26.2.3. r 84
  • IS 456:2000B- For slabs, Z, shall not exceed half the value greater than 230 N/mmz,of Z,milx given in Table 24. a = angle between the inclined stirrup or bent-up bar and the axis of the member,B-5.3 Minimum Shear Reinforcement not less than 45”, andWhen zv is less than zCgiven in Table 23, minimumshear reinforcement shall be provided in accordance d = effective depth.with NOTE -Where more than one type of shear reinforcement is used to reinforcethe same portion of the beam, the total shearB-5.4 Design of Shear Reinforcement resistance shall be computed as the sum of the resistance for the ’ varioustypesseparately. The nrea of the stirrups shall not beWhen zv exceeds zC given in Table 23, shear less than the minimum specified in shall be provided in any of the followingforms: B-5.5 Enhanced Shear Strength of Sections Close a) Vertical stirrups, to supports b) Bent-up bars along with stirrups, and Be5.5.1 General c) Inclined stirrups. Shear failure at sections of beams and cantileversWhere bent-up bars are provided, their contribution without shear reinforcement will normally occur ontowards shear resistance shall not be more than half plane inclined at an angle 30” to the horizontal. If thethat of the~total shear reinforcement. angle of failure plane is forced to be inclined moreShear reinforcement shall be provided to carry a shear steeply than this [because the section consideredequal to V- The strength of shear reinforcement (X - X) in Fig. 24 is close to a support or for otherV, shall be calculated as-below: reasons], the shear force required to produce failure is increased. a) For vertical stirrups The enhancement of shear strength may be taken into account in the design of sections near a support by increasing design shear strength of concrete, z, to 2d zClav provided that the design shear stress at b) For inclined stirrups or a series of bars bent-up the face of support remains less than the values at different cross-sections: given in Table 23. Account may be taken of the enhancement in any situation where the section v,= as, 4, d (sina + cosa) considered is closer to the face of a support of sV concentrated load than twice the effective depth, d. c) For single bar or single group of parallel-bars, To be effective, tension reinforcement should extend all bent-up at the same cross-section: on each side of the point where it~isintersected by a V, = 6,” A,, sin 01 possible failure plane for a distance at least equal to the effective depth, or be provided with anwhere equivalent anchorage. As” = total cross-sectional area of stirrup legs or bent-up bars within a distance, B-5.5.2 Shear Reinforcement for Sections Close to Supports spacing of the stirrups or bent-up bars along the length of~themember, If shear reinforcement is required, the total area of this design shear strength of the concrete, is given by: breadth of the member which for As = avb ( Z, -2d ze/av )/0.87fy 2 0.4avb/0.87fy flanged beams, shall be taken as the This reinforcement should be provided within the breadth of the web b, middle three quarters of a”. Where av is less than d, permissible tensile stress in shear horizontal shear reinforcement will be more effective reinforcement which shall not be taken than vertical. Table 24 Maximum Shear Stress, z, ,_, N/mm* (CluusesB-52.3, B-,B-5.5.1 andB-6.3.1) Concrete Grade M 15 M 20 M 25 M 30 M 35 M40andabove Nhnz zc,,,yx, 1.6 1.8 1.9 2.2 2.3 2.5 85
  • IS 456: 2OOQB-5.5.3 Erihanced Shear Strength Near Supports V = shear,(Simpl$ed Approach) T = torsional moment, andThe procedure given in B-5.5.1 and B-5.5.2 may be b = breadth of beam.used for all beams. However for beams carrying The equivalent nominal shear stress, ‘t,, in this casegenerally uniform load or where the principal load is shall be calculated as given in B-5.1, except forlocated further than 2 d from the face of support, the substituting V by Ve. The values of rVcshallnot exceedshear stress may be calculated at a section a~distanced the values of T _ given in Table 24.from the face of support. The value of 2, is calculated B-6.3.2 If the equivalent nominal shear stress Z, doesin accordance with Table 23 -and appropriate shear not exceed z,, given in Table 23, minimum shearreinforcement is provided at sections closer to the reinforcement shall be provided as specifiedsupport, no further check for such section is required. in TORSION B-6.3.3 If zy, exceeds 2, given in Table 23, both longitudinal and transverse reinforcement shall beB-6.1 General provided in accordance with B-6.4.In structures where torsion is required to maintain B-6.4 Reinforcement in Members Subjected toequilibrium, members shall be designed for torsion in Torsionaccordance with B-6.2, B-6.3 and B-6.4. However, forsuch indeterminate structures where torsion can be B-6.4.1 Reinforcement for torsion, when required,eliminated by releasing redundent restraints, no shall consist of longitudinal and transversespecific design for torsion is necessary provided reinforcement.torsional stiffness is neglected in the calculation of B-6.4.2 Longitudinal Reinforcementinternal forces. Adequate control of any torsional.cracking is provided by the shear reinforcement as The longitudinal reinforcement shall be designed to per B-5. resist an equivalent bending moment, Me,, given by NOTE -The approachto design in this clause for torsionis as Me,=M+M, follows: ‘where Torsional reinforcement is not calculated separately from M = bending moment at the cross-section, and that required~for bending and shear. Instead the total longitudinal reinforcement is determined for a fictitious (l+ D/b) bending moment which is a function of actual bending M,=T 17 , where T is the torsional moment and torsion; similarly web reinforcement is determinedfor a fictitious shearwhich is a functionof actual moment, D is the overall depth of the shear and torsion. beam and b is the breadth of the beam.B-6.1.1 The design rules laid down in B-6.3 B- If the numerical value of M, as definedand B-6.4 shall apply to beams of solid rectangular in B-6.4.2 exceeds the numerical value of the momentcross-section. However, these clauses may also be M, longitudinal reinforcement shall be provided onapplied to flanged beams by substituting b, for b, in the flexural compression face, such that the beam canwhich case they are generally conservative; therefore also withstand an equivalent moment M, given byspecialist literature may be referred to. M,= M,- M, the moment Me2being taken as acting in the opposite sense to the moment M. B-6:2 Critical Section B-6.4.3 Transverse Reinforcement Sections located less than a distance d, from the face of the support may be designed for the same torsion as Two legged closed hoops enclosing the corner computed at a distance d, where d is the effective longitudinal bars shall have an area of cross-section depth. Ali,,given by B-6.3 Shear and Torsion 4, = T.s, + ‘*” , but the total W, Q,, 2.5 d, osv B-6.3.1 Equivalent Shear transverse reinforcement shall not be less than Equivalent shear, V, shall be calculated from the formula: (2, - 2,) b.s, *.w V, = V+1.6$ where where T = torsional moment, V, = equivalent shear, V = shear force, 86
  • Is 456 : 2000s = spacing of the stirrup reinforcement, dli” = permissible tensile stress in shearb: = centre-to-centre distance between corner reinforcement, bars in the direction of the width, z Ye= equivalent shear stress as specified ind, = centre-to-centre distance between comer B-6.3.1, and bars in the direction of the depth, zE = shear strength of-the concrete as specifiedb = breadth of the member, in Table 23. 87
  • IS 456 : 2000 ANNEX C (Ckzuses 22.3.2,23.2.1 and 42.1) CALCULATION OF DEFLECTIONC-l TOTAL DEFLECTION For continuous beams, deflection shall be calculated using the values of Z,, ‘,I and M, modified by theC-l.1 The total deflection shall be taken as the sum of following equation:the short-term deflection determined in accordancewith C-2 and the long-term deflection, in accordance Xc =k Iwith C-3 and C-4. whereC-2 SHORT-TERM DEFLECTION x, = modified value of X,C-2.1 The short-term deflection may be calculated by X,*X, = values of X at the supports,the usual methods for elastic deflections using theshort-term modulus of elasticity of concrete, E, and x, = value of X at mid span,an effective moment of inertia 5, given by the k, = coefficient given in Table 25, andfollowing equation: x= value of I,, 1, or M, as appropriate. C-3 DEFLECTION DUE TO SHRINKAGE ; but C-3.1 The deflection due to shrinkage u_ may be computed from the following equation: 4 a, = k3 Ya l2 wherewhere k3 is a constant depending upon the support I, = moment of inertia of the cracked section, conditions, fcr Igr 0.5 for cantilevers, Iv, = cracking moment, equal to - where Yr 0.125 for simply supported members, f,, is the modulus of rupture of concrete, 0.086 for members continuous at one end, Zgr the moment of inertia of the gross is and section about the centroidal axis, 0.063 for fully continuous members. neglecting the reinforcement, and yt is the distance from centroidal axis of gross is shrinkage curvatureequal to k L section, neglecting the reinforcement, -to ‘D extreme fibre in tension, where E,, is the ultimate shrinkagestrainof concrete M= maximum moment under service loads, (see 6.2.4). Z = lever arm, k,=O.72x 8 - &s l;OforO.25~<-PC< 1.0 X depth of neutral axis, 7 d : effective depth, bw = breadth of web, and = 0.65 x !?j$* l.OforP,-PC> 1.0 b = breadth of compression face. Table 25 Values of Coeffkient, k, (Clause C-2.1)% 0.5 or less 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4k, 0 0.03 0.08 0.16 0.30 0.50 0.73 0.91 0.97 ,.!j.? 1.0NOTE - k2 is given by where M,, Mz = support moments, and %,, M, = fixed end moments. 88
  • IS 456: 2000 wherewhere P I = - loo 41 and P - loo& a. bd ’ bd Mlm)= initial plus creep deflection due to WV permanent loads obtained using an and D is the total depth of the section, and 1 is the elastic analysis with an effective length of span. modulus of elasticity,C-4 DEFLECTION DUE TO CREEP Ece = - Ec ; 8 being the creep coefficient, 1+eC-4.1 The creep deflection due to permanent loadsa ~,perm) may be obtained from the following equation: and a. +3-m) I = short-term deflection due to aU:@emI)a.I.CC - ‘i = @cm~) @cm) permanent load using EC. 89
  • IS 456 : 2000 ANNEX D (Clauses 24.4 and 37.1.2) SLABS SPANNING IN TWO DIRECTIONSD-l RESTRAINED SLABS D-l.6 At a discontinuous edge, negative moments mayD-1.0 When the comers of a slab are prevented from arise. They depend on the degree of fixity at the edgelifting, the slab may be designed as specified in D-l.1 of the slab but, in general, tension reinforcement equalto%1.11. to 50 percent of that provided at mid-span extending 0.1 1 into the span will be sufftcient.D-l.1 The maximum bending moments per unit widthin a slab are given by the following equations: D-l.7 Reinforcement in edge strip, parallel to that edge, shall comply with the minimum given in Section Mx=axwl~ 3 and the requirements for torsion given in D-l.8 M,=a,w1,2 to D-1.10. where D-l.8 Torsion reinforcement shall be provided at any axand % are coefficients given in Table 26, corner where the slab is simply supported on both edges meeting at that corner. It shall consist of top w= total design load per unit area, and bottom reinforcement, each with layers of bars Mx,My = moments on strips of unit width placed parallel to the sides of the slab and extending spanning LXand 1, respectively, from the edges a minimum distance of one-fifth of and the shorter span. The area of reinforcement in each of lx and 1 = lengths of the shorter span and these four layers shall be three-quarters of the area Y longer span respectively. required for the maximum mid-span moment in the slab.D-l.2 Slabs are considered as divided in each directioninto middle strips and edge strips as shown in Fig. 25 D-l.9 Torsion reinforcement equal to half thatthe middle strip being three-quarters of the width and described in D-l.8 shall be provided at a cornereach edge strip one-eight of the width. contained by edges over only one of which the slab is continuous.D-l.3 The maximum moments calculated as in D-l.1apply only to the middle strips and no redistribution D-1.10 Torsion reinforcements need not be providedshall be made. at any comer contained by edges over both of whichD-l.4 Tension reinforcement provided at mid-span in the slab is continuous.the middle strip shall extend in the lower part of the D-l.11 Torsion ly / 1, is greater than 2, the slabsshallslab to within 0.25 1 of a continuous edge, or 0.15 1 of be designed as spanning one way.a discontinuous edge. D-2 SIMPLY SUPPORTED SLABSD-1.5 Over the continuous edges of a middle strip,the tension reinforcement shall extend in the upper part D-2.1 When simply supported slabs do not haveof the slab a distance of 0.15 1 from the support, and at adequate provision to resist torsion at corners and toleast 50 perccent shall extend a distance of 0.3 1. prevent the corners from lifting, the maximum l----+1 I J-L I--+’ I T- EDGE STRIP _--__-____--__-___ alo I t I -7 2 EDGE1 MIDDLE STRIP SEDGE 3 3 STRlPl ISTRIP MIDDLE STRIP rrh 1, ’ I I i w---- - ------ -____l ’ i EDGE STRIP ,4 -+ 25A FOR SPAN I, 25B FOR SPAN ly FIG. 25 DIVISIONOF SLAB INTOMDDLE AND EDGE STRIPS on
  • IS 456 : 2000 Table 26 Bending Moment Coeffuzients for Rectangular PaneIs Supported on Four Sides with Provision for Torsion at Comers (ClausesD-l .l and 24.4.1)Case Type of Panel and Short Span Coeffkients a, Long SpanNo. Moments Considered (values of I,“,, Coefficients ay for All , . Valuesof 1.0 1.1 1.2 1.3 1.4 1.5 1.75 2.0 ‘YK(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Cl1)I Interior Punels: Negative moment at continuous edge 0.032 0.037 0.043 0.047 0.05 1 0.053 0.060 0.065 0.032 Positive moment at mid-span 0.024 0.028 0.032 0.036 0.039 0.041 0.045 0.049 0.0242 One Short Edge Continuous: Negative moment at continuous edge 0.037 0.043 0.048 0.051 0.055 0.057 0.064 0.068 0.037 Positive moment at mid-span 0.028 0.032 0.036 0.039 0.041 0.044 0.048 0.052 0.0283 One h)ng Edge Discontinuous: Negative moment at continuous edge 0.037 0.044 0.052 0.057 0.063 0.067 0.077 0.085 0.037 Positive moment at mid-span 0.028 0.033 0.039 0.044 0.047 0.051 0.059 0.065 0.0284 7klo Adjucent Edges Discontinuous: Negative moment at continuous edge 0.047 0.053 0.060 0.065 0.071 0.075 0.084 0.091 0.047 Positive moment at mid-span 0.035 0.040 0.045 0.049 0.053 0.056 0.063 0.069 0.0355 Two Short Edges Discontinuous: Negative moment at continuous edge 0.045 0.049 0.052 0.056 0.059 0.065 0.069 - Positive moment at mid-span 0.035 0.037 0.040 0.043 0.044 0.045 0.049 0.052 0.0356 Two Edges Discontinuous: Negative moment at continuous edge - - - - - - - 0.045 Positive moment at mid-span 0.035 0.043 0.05 1 0.057 0.063 0.068 0.080 0.088 0.0357 Three Edges Discontinuous (One Long Edge Continuous): Negative moment at continuous edge 0.057 0.064 0.071 0.076 0.080 0.084 0.091 0.097 - Positive moment at mid-span 0.043 0.048 0.053 0.057 0.060 0.064 0.069 0.073 0.0438 Three Edges Discrmntinunus (One Shor? Edge Continuous) : Negative moment at continuous edge - - - - - - - - 0.057 Positive moment at mid-span 0.043 0.051 0.059 0.065 0.07 1 0.076 0.087 0.096 0.0439 Four-Edges Discontinuous: Positive moment at mid-span 0.056 0.064 0.072 0.079 0.085 0~089 0.100 0.107 0.056moments per unit width are given by the following and ax and ay are moment coefficientsequation: given in Table 27 M, = a, w 1,2 D-2.1.1 At least 50 percent of the tension reinforcement provided at mid-span should extend M, =izy wl; to the supports. The remaining 50 percent should where extend to within 0.1 fX or 0.1 f of the support, as Mx, My, w, lx, I, are same as those in D-1.1, appropriate. Table 27 Bending Moment Coeffkients for Slabs Spanning in l’ko Directions at Right Angles, Simply Supported on Four Sides . (Clause D-2.1) $4 1.0 1.1 1.2 1.3 1.4 1.5 1.75 2.0 2.5 3.0 ax 0.062 0.074 0.084 0.093 0.099 0.104 0.113 0.118 0.122 0.124 aY 0.062 0.061 0.059 0.055 0.05 1 0.046 0.03; 0.02% 0.020 0.014 91
  • IS 456 : 2000 ANNEX E (Chse 25.2) EFFECTIVE LENGTH OF COLUMNSE-l In the absence of more exact analysis, the effective E-2 To determine whether a column is a no sway orlength of columns in framed structures may be obtained a sway column, stability index Q may be computed asfrom the ratio of effective length to unsupported length given below :1,/f given in Fig. 26 when relative displacement of theends of the column is prevented and in Fig. 26 whenrelative lateral displacement of the -ends is notprevented. In the latter case, it is recommendded that wherethe effective length ratio Id/l may not be taken to be VU = sum of axial loads on all column in theless than 1.2. storey, Au = elastically computed fust order lateral NOTES deflection, 1 Figures 26 and 27 nre reproduced from ‘The Structural Hu = total lateral force acting within the Storey, Engineer’ No. 7, Volume 52, July 1974 by the permission of the Council of the Institution of StructuralEngineers, and U.K. h, = height of the storey. 2 In Figs. 26 and 27, p, and p, a~ equal to xc If Q 5 0.04, then the column in the frame may be taken as no sway column, otherwise the column will be I;K,+=b considered as sway columnn. where the summation is to be done for the members fmming into njoint st top nnd bottom respectively; nndKc E-3 For normal usage assuming idealizedconditions. und K, being the flexural stiffness for column and benm the effective length 1, of in a given plane may be respectively. assessed on the basis of Table 28. H INGED FIXED FIG.26 EFFECIWELENGTH RATIOS A COLUMNIN A FRAME FOR WITH SWAY NO 92
  • IS 456 : 2000HINGED1.O 0.8 0.7 0.6 1 P, Oa5 0.4 0.3 0.2 0.1FIXED 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 FIG.27 EFFECTIVE RATIOS A COLUMN A LENGTH FOR TN FRAMEWITHOUT RESTRAINT AGAINSTSWAY 93
  • IS 456 : 2000 Table 28 Effective Length of Compression Members (Clause E-3)Degree of End Symbol Theoretical RecommendedRestraint of Compre- Value of Value ofssion Members Effective Effective (1)Effectively held in (2) / Length (3) 0.50 1 Length (4) 0.65 1 1position and restrainedagainst rotation inboth ends I , IlIzEffectively held in 0.70 1 0.80 1 .1position at both ends, Irestrained against trotation at one end /Effectively held in 1.001 1.00 1position at both ends,but not restrainedagainst rotation r-1Effectively held in 1.00 1 1.20 1 Lposition and restrained LI’against rotation at oneend, and at the other //restrained againstrotation but not heldin positionEffectively held in - 1.50 1position and restrainedagainst rotation inone end, and at theother partially restr-ained against rotationbut not held in position 2.00 1Effectively held in El 2.00 1 Lposition at one endbut not restrainedagainst rotation, andat the other end restrained :against rotationbut not held in position ,Effectively held in 2.00 1 2.00 1 /’ 4,position and restrainedagainst rotation at one /end but not held inposition nor restrainedagainst rotation at theother end NOTE - 1 is the unsupported length of compression member. 94
  • IS 456: 2000 ANNEXF (Clauses 35.3.2 and 43.1) CALCULATION OFCKACK WIDTHProvided that the strain in the tension reinforcement X= the depth from the compression face to theis limited to 0.8 FYI Es, the design surface crack width, neutral axis,which should not exceed the appropriate value given the maximum compressive stress in the f,=in 35.3.2 may be calculated from the following concrete,equation: f,= the tensile stress in the reinforcement, andDesign surface crack width Es = the modulusof elasticityof the reinforcement 3% Em Alternatively, as an approximation, it will normally KY = be satisfactory to calculate the steel stress on the basis 1 + 2( a,, - Girl ) of a cracked section and then reduce this by an amount h-x equal to the tensile force generated by the triangularwhere distributions, having a value of zero at the neutral axis a SC = distance from the point considered to the and a value at the centroid of the tension steel of surface of the nearest longitudinal bar, 1N/mm2 instantaneously, reducing to 0.55 N/mm2 in Cme m=minimum cover to the longitudinal bar; the long-term, acting over the tension zone divided by the steel area. For a rectangular tension zone, this gives E, = average steel strain at the level considered, h = overall depth of the member, and b (h-x)(a-x) E, = &I - = depth of the neutral axis. 3E, A&X)’ x whereThe average steel strain E, may be calculated on thebasis of the following assumption: As = area of tension reinforcement,The concrete and the steel are both considered to be b = width of the section at the centroid of thefully elastic in tension and in compression. The elastic tension steel,modulus of the steel may be taken as 200 kN/mm2 and E, = strain at the level considered, calculatedthe elastic modulus of the concrete is as derived from ignoring the stiffening of the concrete inthe equation given in both in compression and the tension zone,in tension. a = distance from the campression face to theThese assumptions are illustrated in Fig. 28, point at which the crack width is beingwhere calculated, and h = the overall depth of the section, d = effective depth. I- III tl 0 SECTION As 0 CRACKED STRAIN FIG.28 STRESS STRESS IN CONCRETE 1 N/mm2 IN SHORT TERM 0.SSNlmm2 IN LONO TERM 95
  • IS 456 : 2000 ANNEX G (Clause 38.1) MOMENTS OF RESISTANCE FORRECTANGULARAM) T-SECTIONSG-O The moments of resistance of rectangularand exceeds the limiting value, MU ,imcompressionT-sections based~onthe assumptions of 38.1 are given reinforcement may be obtained from the followingin this annex. equation :G-l RECTANGULARSECTIONS Mu - Mu,,h=fJlf (d-d’)G-l.1 SectionsWithoutCompression whereReinforcement Mu, M,, lirn’ are same as in d G-1.1,The moment of resistance of rectangular sections f,= design stress in compression reinforce- ’without compression reinforcement should be obtained ment corresponding to a strain ofas follows : a) Determine the depth of netutral axis from the XII, -6’) max 0.003 5 ( following equation : %I,max xu= 0.87 fY $t where d 0.36 f,k~b.d xu.maa= the limiting value of xU_from38.1, b) If the value of x,/d is less than the limiting AX = amaof~onreinforcemen~ and value (see Note below 3&l), calculate the d’ = depth of compression reinforcement moment of resistance by the following from compression face. expression : The total area of tension reinforcement shall be obtained from the following equation : 4t fy M” = 0.87 fy bt d 1 -- ( bd fck 1 Ast=Ast* f42 c> If the value of xu/d is equal to the limiting 4 = area of the total tensile reinforcement, value, the moment of resistance of the section As,‘ = area of the tensile reinforcement for a is given by the following expression : singly reinforced section for Mu lim, andMu = 0.36 F *lim 1 -0.42 y bd2 fct Ast* = Axfwl 0.87fy. d) If xU/ d is greater than the limiting value, the G-2 FLANGED SECTION section should be redesigned.In the above equations, G-2.1 For xU<D, the-moment of resistance may be calculated from the equation given in G-1.1. x = depth of neutral axis, ;; = G-2.2 Thelimiting value of the moment of resistance effective depth, of the section may be obtained by the following & = characteristic strength of reinforce- equation when the ratio D, / d does not exceed 0.2 : ment, 4 = area of tension reinforcement, . f& = characteristic compressive strength . of concrete, b = width of the compression face, Mu.lim = limiting moment of resistance of a section without compression where reinforcement, and M”,x”.~*~d andf, are same as in G-1.1, x = limiting value of x, from 39.1. b, = breadth of the compression face/flange, u.-G-l.2 Sectionwith CompressionReinforcement bw= breadth of the web, andWhere the ultimate moment of resistance of section D, = thickness of the flange. 96
  • IS 456 : 2000G-22.1 When the ratio D,/d exceeds 0.2, the moment where yr = (0.15 xU + 0.65 DJ, but not greater than~of resistance of the section may be calculated by the D, and the other symbols are same as in G-l.1following equation : and G-2.2. G-2.3 For xUmilx x, > Q,, the moment of resistance > M, ~0.3695 l-0.42- fckbwd2 may be calculated by the equations given in G-2.2 ( 1 when D,.lx, does not exceed 0.43 and G-2.2.1 when D/x,, exceeds 0.43; in both cases substituting x,, milx by x;. 97
  • IS 456 : 2000 ANNEX H ( Foreword ) COMMITTEE COMPOSITION Cement and Concrete Sectional Committee, CED 2 Chuirman DRH. C. V~SWSVARYA ‘Chandrika’, at 15thCross, 63-64, Malleswaram, Bangalore 560 003 Members RepresentingDR S. C. AHLUWAL~A OCL India, New DelhiSHRI G. R. BHARTIKAR B. G. Shirke & Construction Technology Ltd. PuneSHRI N. TIWARI T. The Associated Cement Companies Ltd, Mumbai DR D. GHOSH(Alternute)CHIEF ENGINEER (DESIGN) Central Public Works Department, New Delhi SUPERIK~N~ING ENGINEER (S&S) (Alternate)CHIEF ENGINEER, NAVAGAM DAM Sardar Sarovar Narman Nigam Ltd. Gandhinagar SUPERIN~NLNNG ENGINEER @CC) (Alternate)CHIEF ENGINEER (RE~EAR~WC~M-DIRECTOR) Irrigation and Power Research Institute, Amritsar RESEARCH OFFICER (CONCRETE TECHNOLOGY) (Alternate)DIRECWR A.P. Engineering Research Laboratories, Hyderabad JOINT DIRECXUR (Alternate)DIRECTOR (CMDD) (N&W) Central Water Commission, New Delhi DEPUTY DIRECWR(CMDD) (NW&S) (Alternate)SHRI H. GANGWAL K. Hyderabad Industries Ltd. Hyderabad SHRI PA~ABHI V. (Altemute)SHRI K. GHANEKAR V. Structural Engineering Research Centte (CSIR), GhaziabadSHRI GOPMATH S. The India Cements Ltd, Chennai SHRI TAMILAKARAN R. (Alrernu?e)SHRI K. GUHATHAKWRTA S. Gannon Dunkerley & Co Ltd. Mumbai SHRI P. SANKARANARAYANAN S. (Alternate)Suai N. S. BHAL Central Building Research Institute (CSIR), Roorkee DR IRSHAD MASOOD(Alremate)SHRI C. JAIN N. Cement Corporation of India, New DelhiJOINT DIREWR STANDARDS (B&S) (CB-I) Research, Designs & Standards Organization (Ministry of Railway), JOINT DIRECTOR STANDARDS (B&S) (CB-II) (Akenrate) LucknowSHRIN. G. JOSHI Indian Hume Pipes Co Ltd. Mumbai SHRI D. KELKAR P. (Altemute) SHRI K. KANIJNOO D. National Test House, Calcutta SHRI B.R. MEENA(Alternute) SHRI P. KRISHNAMIJ~ Larsen and Toubro Limited, Mumbai SHRI CHAKRAVARTHY S. (Alternate) DR A. G. MADHAVARAO Structural Engineering Research Centre (CSIR), Chennai SHRI MANY K. (Alfemute) SHRI SARUP J. Hospital Services Consultancy Corporation (India) Ltd, New Delhi SHRI PRAF~LLA KUMAR Ministry of Surface Transport, Department of Surface Transport SHRI P. NAIR(Afternute) P. (Roads Wing), New Delhi . (Continued on page 99) 98
  • IS 456 : 2000(Conkwed,from puge 98) Members RepresenhgMEMBERSECRETARY Central Board of Irrigation and Power, New Delhi DIRECVLIR (CIVIL) (Alternute)SHRIS. K. NATHANI, I SO Engineer-in-Chief’s Branch, Army Headquarters, New Delhi DR A. S. GOEL, (A&mute) EESHRIS. S. SEEHRA Central Road Research Institute (CSIR), New Delhi (Altemute) SHRISATAN~ERKUMARSHRIY. R. PHULL Indian Roads Congress, New Delhi SHRIA. K. SHARMA (Alterflute)DR C. RAJKUMM National Council for Cement and Building Materials, New Delhi DR K. MOHAN(Alrernure)SHRIG. RAMDAS Directorate General of Supplies and Disposals, New Delhi (Alrernute) SHRIR. C. SHARMASHRIS. A. REDDI Gammon India Ltd. MumbaiSHRIJ. S. SANGANER~A Geological Survey of India, Calcutta SHRIL. N. AGARWAL(Alternute)SHRIVENKATACHALAM Central Soil and Materials Research Station, New Delhi (Alternute) SHRIN. CHANDRASEKARANSUPERIIWENDING ENGINEER(DESIGN) Public Works Department, Government of Tamil Nadu, Chennai EXECUTWE (S.M.R.DWISION) (Altemure) ENGINEERSHRI A. K. CHADHA Hindustan Prefab Ltd. New Delhi _SHRI R SIL (Alrernule) J.DR H. C. VISVESVARAYA The Institution of Engineers (India), Calcutta (Alternure) SHRID. C. CHATURVEDI SHRIVINODKUMAR Director General, BIS (Ex-@icio Member) Director (Civ Engg) Member-Secreluries SHRIJ. K. PRASAD Add1Director (Civ Engg), BIS SHRISAWAYPANT Deputy Director (Civ Engg), BIS Panel for Revision of Design Codes Convener DR C. RAJKUMAR National Council for Cement and Building Materials, Ballabgarh Members SHRI V. K. GHANEKAR Structural Engineering Research Centre, Fhaziabad SHRI S. A. REDDI Gammon India Ltd. Mumbai SHRIJOSE KURIAN Central Public Works Department, New Delhi DR A. K. MITTAL Central Public Works Department, New Delhi DR S.C.MAITI National Council for Cement and Building Materials, Ballabgarh DR ANn KUMAR(Alremute) PROFA.K. JAIN University of Roorkee, Roorkee DR V. THIRUVENGDAM School of Planning and Architecture, New Delhi (Continued on puge 100) 99
  • IS 456 : 2000 Special Ad-Hoc Group for Revision of IS 456 Convener DR H.C. VISVESVARYA ‘Chandrika’ at 1~5th Cross, 63-64, Malleswamm, Bangalore 560 003 Member.vSHRI S.A. REDDI Gammon India Ltd. MumbiDR C. RAJKUMAR National Council for Cement and Buildidg Materials, Ballubgarh 100
  • Bureau of Indian StandardsBI S is a statutory institution established under the Bureau of Indian Standards Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification of goodsand attending to connected matters in the country.CopyrightBIS has the copyright of all its publications. No part of these publications may be reproduced in anyform without the prior permission in writing of BIS. This does noi. preclude the free use, in the courseof implementing the standard, of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (Publications), BIS.Review of Indian StandardsAmendmerfts are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicatesthat no changes are needed; if the review indicates that changes are needed, it is taken up for revision.Users of Indian Standards should ascertain that they are in possession of the latest amendments~oredition by referring to the latest issue of ‘BIS Catalogue’ and ‘Standards: Monthly Additions’.This Indian Standard has been developed from Dot: No. CED 2(5525) - Amendments Issued Since Publication Amend No. Date of Issue Text Affected BUREAU OF INDlAN STANDARDSHeadquarters:Manak Ehavan, 9 Bahadur Shah Zafar Marg, New Delhi 110 002 Telegrams : ManaksansthaTelephones : 323 01 3 I, 323 33 75, 323 94 02 (Common to all offices) Regional Offices : Telephone Central : Manak Bhavan, 9 Bahadur Shah Zafar Marg { 323 76 17 NEW DELHI 11’6.002 323 38 41 Eastern : l/l 4 C. I. T. Scheme VII M, V. I. P. Road, Kankurgachi { 337 84 99,337 85 61 CALCUTTA 700 054 337 86 26,337 9120 Northem : SC0 335-336, Sector 34-A, CHANDIGARH 160 022 { 60 38 43 60 20 25 Southerw : C. I. T. Campus, IV Cross’ Road, CHENNAI 600 113 { 235 02 16,235 04 42 235 15 19,23523 15 Western : Manakalaya, E9 MIDC, Marol, Andheri (East) 832 92 95,832 78 58 MUMBAI 400 093 { 832 78 91,832 78 92 Branches : AHMADABAD. BANGALORE. BHOPAL. BHUBANESHWAR. COIMBATORE. FARIDABAD. GHAZIABAD. GUWAHATI. HYDERABAD. JAIPUR. KANPUR. LUCKNOW. NAGPUR. PATNA. PUNE. RAJKOT. THIRUVANANTHAPURAM. Rhkd at NCW India Rinting Ress, Khurja, India
  • AMENDMENT NO. 1 JUNE 2001 TO IS 456:2000 PLAIN AND REINFORCED CONCRETE — CODE OF PRACTICE (Fourth Revision ) (Page 2, Foreword last but one line) — Substitute ‘ACI 318:1995’ for ‘ACI 319:1989’. (Page 11, clause 4) – Delete the matter ‘L~ – Horizontal distance between centres of lateral restraint’. (Page 15, clause 5.5, Tide ) — Substitute ‘Chemical Admixtures’ for ‘Admixtures’. (Page 17, clause 7.1 ) — Substitute the following for the existing informal table: Placing Conditions Degree of Slump Wo;kabijity (mm) (1) (2) (3)Blinding concrete;Shallow sections; Very low See 7.1.1Pavements using pavera }Mass concretq ILightly reinforcedsections in slabs,beams, walls, columns; Low 25-75Floors; ‘1Hand placed pavements;Canal liningStrip footingaHeavily reinforcedsections in slabs, Medium 50-100beams, walls, columns;Slipfonn worlq Medium 75-1ooPumped concrete 1Trench fill; High 100-150In-situ piling 1Tremie concrete Very high See 7.1.2 NOIE — For moat of the placing eonditiona, internal vibrarora (needle vibratota) am suitable. ‘lhe diameter of the oecdle ahatl be determined based on the density and apaang of reinformment bara and thickness of aectiona. For tremie eoncret% vibratora are not required to be Used(ace ako 13.3).” (Page 19, Table 4, column 8, sub-heading ) – Substitute %w’ for ‘FMx’ . (Page 27, clause 13.S.3 ) — Delete. (Page 29, clause 15.3 ): a) Substitute ‘specimens’ for ‘samples’ in lines 2,6 and 7. b) Substitute ‘1S9013’ for ‘IS 9103’. ( Page 29, clause 16.1) — Substitute ‘conditions’ for ‘condition’ in line 3 and the following matter for the existingmatter against ‘a)’ : ‘a) The mean strength determined from any group of four non-overlapping consecutive teat results mmplies with the appropriate limits in column 2 of Table 11.’ (Page 29, clause 16.3,para 2 ) — Substitute ‘cd 3’ for ‘cd 2’. -(Page 29, clause 16.4, line 2) — Substitute ‘16.1 or 16.2 as the case may be’ for ‘16.3’. (Page 30, Tablk 11, column 3 ) — Substitute % fek -3’ for ‘a~k-3’ and ‘2A, -4’ for ‘a~k-4’Price Group 3 1
  • Amend No. 1 to IS 4S6: 2000 (Page 33, clause 21.3, line 2) — Substitute !action’ )lor ‘section’. [ Page 37, clause 23.1.2(c)] — Substitute ‘L+‘@r ‘b,’, ‘lO’@ ‘l;, ‘b’ /br ‘b’ and ‘bW’for ‘bW’ the formulak. m (Page 46, clause 26.4.2 ) – Substitute ‘8.2.2’ for ‘8.2.3’. [Page 49, clause (c) (2), last line ] — Substitute ‘6 mm’ for ’16 mm’. (Page 62, clause 32.2.5 ) – Substitute ‘H:’ for ‘HW~’ the explamtion of e,. in (Page 62, clause 32.3.1, line 4) – Substitute ‘32.4’ for ‘32.3’. [ Page 62, clause 32.4.3 (b), line 6 ] — Insert ‘~eW’ etween the words ‘but’ and ‘shall’. b [ Page 65, clause 34.2.4.l(a), last line] — Insert the following after the words ‘depth of footing’: ‘in case of footings on soils, and at a distsnm equal to half the e~fective depth of footing’. (Page 68, Tab& 18, CO14 ) — Substitute ‘-’ for ‘1.0’ against the Load Combination DL + IL. (Page 72, clause 40.1 ) – Substitute ‘bd’ for ‘b~’ in the formula. (Page 83, clause B-4.3, line 2) —Delete the word ‘and’. (Page 85, clause B-5.5.l,para 2, line 6 ) – Substitute ‘Table 24’ for ‘Table 23’. (Page 85, clause B-5.5.2 ) — Substitute the following for the existing formula: ‘A, = avb (tv-2d~c I av) /a,v z 0.4 avb / 0.87 fy’ (Page 90, clause D-1.11, line 1 ) — Substitute ‘Where” for ‘Torsion’. (Page 93, Fig. 27) — Substitute ‘lJ1’ for ‘U’. q (Page 95, Anncw F ): a) The reference to Fig. 28 given in column 1 of the text along with the explanation of the symbols used in the Fig. 28 given thereafter maybe read just before the formula given for the rectangular tension zone. b) Substitute ‘compression’ for ‘compression’ in the explanation of symbol ‘a ‘ . (Pages 98 to 100, Annex H) – Substitute the following for the existing Annex: ANNEX H (Foreword) COMMTfTEE COMPOSITION Cement snd Concrete Sectional Committee, CED 2 Chairman DR H. C. VWESVARAYA ‘Chandnks’. at 15* Cmaa. 63-64 East park Road. A4atieawarsm Bangalore-560 003 ‘ Medurs Reprcssnting DRS. C. AHLUWAUA OCL India I& New Delhi SHRIV. BAIASUSrMWUWAN Directorate Geneml of Supplies and Dwpoask New Delhi SHIUR. P. SINGH(Alternate) SHFU R. BHARtmwtr G. B. G. Shirke Construction Technology L@ Puoe SHRIA K CHADHA Hindustsn Prefab IJmite4 New Delhi SHIUJ.R. !ML(Ahenrute) CMrrw ENGtmeR(DtmoN) Central Pubtic WortraDepartment, New Delhi SUFSRNIINDING ENOtNSER&S) (Alternate) CIMIFENOINSWI @IAVGAMDAMI Sardar Samvar Namrada Nigsm L&t,Gamfhinagar SUFSmmNOINGENoumut(QCC) (Alterrrde) CHIEF thGINSF!JIRBswRcH)-cuM-IlttecmR ( Irrigation aridPower Research Inatihrte. Amritssr R@sSARCH OFPICaR@ONCREIIi ‘kHNOLOGY) (Akernde) 2 (contimdrmpsge3)
  • Amend No. 1 to IS 456:2000( Continuedfiompage 2 ) Madera Jieprcseti”ngSHRIJ.P. DESM Gujarat Arnbuja Cemenla Ltd, Ahmedabad SHRtB. K JAGETIA (Ahernot.)DRIX.TOR AP. EngineeringResearchI.Axxatoris Hyderabad JOINT DItUKTOR@keMOte)DtREct_OR (CMDD) (N&W CentralWater Commission,New Delhi DEPrnYDIRtXNIR(CMDD) (NW&S) (Af&rnate)Stint K H. GANGWAL HyderabadIndustriesLtd, Hyderabad %ltt V. pATrABHl (Ab7@e)SHIUV.K Gwuwrmrr Structural EngineeringResrmcb Centre (CSIR), GhaziabadSHRI . GOPtWITH S Tire IndiaCements Ltd, Chennai SttruR. TAMUKAMN (A/krnate)SHWS.K GUHATHAKURTA GannonDunkerleyand Companyw Mumtil SHRtS.SANKARANARAYANAN (Akrnate)SNRI . S. BNAL N Central BuildingResearehInstitute(cSIR), Roorkee DRIRSHAD ,SGGD(AktwIot.) MPROF K JAIN A. Univemityof Roorkee,RoorkeeSHRtN.C. JAIN Cement Corporation of India Ud, New DelhiJOttWDtRXTOR@TANDARDS) (CB-f) (B&S) Rese.mcb,Designs& StandardaOrganization(Mlniatryof Railways>Luekmw Jomrr IMF.CTGR(STANOAIUW (B&S) (cB-II) (Alternote)SHRJ G. Josra N. The IndianHume Pipe CompanyI@ Mumbai SmuP. D. IQrumrt (Afterde)St+trrD.KKANUNoo NationalTest HouaGCalcutts SHRJB.R. Mt?ENA (Akernote)sHRIP. KRlaHN4MuRlHY Larsen& TubroM Mumbai Smt S. CHOWDHURY (Akernoti) RAODRA. G. MADHAVA Structurall?ngineeringReseamhCcntre (CSIR> Cbennai Smu K MAM (Akermrte)St+ruJ.SARW HospitalServi~ ComsuhsncyGwpmation (hdw) m New Ddbi%lltV. Housingand Urbsn DevelopmentCorporationLQ New Delhi SHRID.P. SINGH@&?mate)SW PtwwrA KUMAR Ministryof SurfaceTrsnapo@Departmentof SurfaceTrsnaport(Rnsds WI@ New Delhi SHRtp.P. NAIR(AIternate)MmmtmSF.CRRTARY CentralBoard of Irrigation& Power, New Delhi D(~R(CML)(A/t=ti&)SHRIS.KN.AMMNI Engineer-inChiefs Branch, Army HeaifquartemNew Delhi DRA S. Gorz (Akmde)SHRIS. S. SriEHRA Central Road ResearehInstitute(CSIR), New Delhi Swtt SATANDER UMAR(Akerwde) KSHRIY. R.PHUU IndmnRoadaCm- New Delhi SHRtA K SHARMA (Akrurte)DRC. RAJKUMAR NationalCouncil for Cement and BuildingMaterials Baflabgsrh DR K MOHAN(Aft~)sHRtS. A Rt3DDI Gammon Indw L@ MumbaitiR15E!WAllVB Builder’skoeiition of Indw, MumbaiSHRIJ.S. SANO~ GeologicalSurvrYyf Indm,Calcutta o Smt L N. AOARWAL(A/le/?@e)suPERtNmmN G BNGtNEER(Dt?stGN) Public Works Departmen$Guvemmentof Tamil Nadq Cbermai EXKIMVE ENouwER(SMR DtvtsioN)(4ternde)Stint K K TAPARM IndmnRayon sod Industries~ Pune SHRIA K JAN (Akd4SHRIT. N. TIWARI 7% Aaociated ~ment Ckmpaniesw Mumbai DRD. GHOStI ternute) @DitK VENKATMXUAM Central Soil and Materials ResearebStatioq New Delhi SwuN. CHANDWWXARAN (Alternate) 3 ( Continued onpcrge 4 )
  • Amend No. 1 to IS 456:2000( Continued fiunpage 3) Makers Rep-”ngDRH. C. VtSVESVARAYA llre Institutionof Engineers(India) Calcutta SmuD. C. CHATUItVEOJ(AkUW@SHRJVtNOD UMAR K DirectorGeneral,BtS (Ex-oficio Member) Dkector (Civ Engg) Member-.%rdark$ SHRIJ. K PRASAO Additional Dkcctor (Ctv Engg), BIS SHRISAIWAY PANT Deputy Dkector (Civ Engg), BIS Concrete Subeomrnittee,CE1322 Com.wser RepresentingDRA K MUUJCK National Council for Cement and Building Materials,.Ballabgarh MemberssHRtC. R. AuMcHANOAM Stup Consultants Ltd, Mumbai Smu S. RANGARAIAN (Altemute)DR P. C. CHOWDHURY Torsteel Research Foundation in India, Calcutta (Alternate) DR C. S. VtSHWANAITMSHRSJ.P. DESN Gujarat Ambuja Cements Ltd, Ahmcrtabad Srab B. K JAGETIA (Alf.rwt.)DtIGZTOR Central Soil and Materials Research Station, New Delhi SNRIN. CHANDRASmCARAN (Akerrrate) DtRMXOR (C8CMDD) Central Water Commision, New Delhi DF,PGTYrrwcmR (C&MDD) (Alternate) D JOtNTD~RSTANDAttOS @8@CB-H Researc~ Designs and Standards Organintion ( Ministry of Railways), Lucknow JOSNT tR@CITIRSTANDARDS D (EWS)KB-I (Alternate)StJPEWTEHDtNGENGtNEEJt (DI?SIGNS) Central Public Works Department New Delhi EmxrmvEENotN@sR(DEsIGNs)-111 (Alt.rnok)StmtV. K. GHANEKArr Structural Engineering Research Centre (CSIR), Gt@abad WirrtD. S. PRAKASHIUO(Allerrrote) SHRSS. K GGHATHAKURTA Gannon Dunkedey and Co Ltd, Mwnbai sHRrs. P. sANmRmwm YANAN(Alternate) SHRIJ.S. HINoorwo Assoaated Consulting Services, Mumbai stint LKJMN In personal capacity Smtt M. P. JAtSINGH Central Building Research Institute (CSIR), Roorkec DR B. KAMISWARARAO(Alternate) CHIEFENGtNEeR JOtNT & SGCRSTARY Public Works Dcpartmenh MumL-A srJP51uNTmm ENOSNSSR SNO (Alternate) PROFS. KstrsHNAMOORIHY Indian Institute of Technology, New Delhi SHRI K K. NAYAR(Akernute) DRS. C. Wvn National Counal for Cement and Building Material%Ballabgsrh MANAGINODtREIXIR HitsdustanPrefab Limited, New Delhi .%mtM. KUNDSJ (Alternate) sHRts. KNNrmNI Engineer-in-Chief’s Branch, Army Headquarters, New Delhi LT-COL S. fXARAK K (Alternate) Stint B. V. B. PAI The Associated Cement Companies L$4Mumtil StrroM. G. DANDVATB(Alternate) SHWA. B. PHADKB llre Hindustsn Construction Co Lt4 Mumbai SHRID. M. SAWR (Alternate) SHRJY. R PHUU Central Road Research Institute (CSIR),-New Delhi Wttt S. S. SSSHRA (A/ternofe I) KttMAR(Alternate H) SW SATANGER 4 (Carthuedonpsrge5)
  • Amend No. 1 to IS 4S6: 2000( Contirtwd frcvnpog. 4) RepresentingStno A. S. PRASAD RAO Structural Engineering Research Centre (cSIR), Chennai StlR1K. MAN] Aherrrote) (SHRI K. L PRUrHJ National Building Construction Corporation Ltd. New Delhi SHRIJ. R. GAtSR.JEL (A/terrrufe)SHrtI B. D. RAHALIWR Nuclear Power Corporation Ltd, New Delhi SHRI U. S. P. VERMA(Alternate)SHRI HANUMANTHARAO A.P. Engineering Research Laboratories, Hyderabad SHRIG. RAMAKRtStlNAN (Alternate)SHto S. A. REDDI Gammon India Ltd. Mumbai DR N. K. NAYAK (Ahernde)S}IRI S. C. SAWHNEY Engineers India Ltd, New Delhi StiRl R. P. MEtlR071r,4 (Ahernde)PROFM. S. SHEtTt Indian Concrete Institute, CherrnaiSHRI N. K SINHA Ministry of Surface Transport (Roads Wing), New DelhiSIIRI B. T. UNWAtJA In personal capacity Panel for Revision of IS 456, CED 2:2/P Convener Reprwenting DR C. RAJKUMAR National Council for Cement and Building Materials, Ballabgarh MembersDR ANILKUMAR National Council for Cement and Building Materials, BallabgarhSIIRJ K. GHANEKAR V. Structural Engineering Research Cenire (cSIR), GhaziabsdPROF K. JAIN A. University of Roorkee, RoorkeeSHRI L K. JAIN In personal capacitySHRIJOSE KURtAN Central Public Works Department, New DelhiDR S. C. MAtTS National Council for Cement and Building Materials, BallabgarhDR A. K MIITAL Central Public Works Department, New DelhiS}IR} S. A. REDOI Gammon India I@ MumbaiDR V. THIRWENGDAM School of Planning and Architecture, New Delhi Special Ad-Hoc Group for Revision of 1S 456 Chairman DR H. C. VISVESVARAYA ‘Chandrika’, at 15* Cross, 63-64 East Park Road, Malleswaram, Bangalore-560 003 Members Representbig DR C. RAJKUMAR National Council for Cement and Building Materials, Ballabgarh SIIRI S. A. REDDI Gammon India Idd, Mumbai (CED2) Printed at New Incha Prmturg Press. KhurJa. India