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Structural design including disaster (wind & cyclone land slide_eq_ resistant design of structures

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Structural design including disaster (wind & cyclone land slide_eq_ resistant design of structures

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Structural design including disaster (wind & cyclone land slide_eq_ resistant design of structures

  1. 1. ‘Structural Design including Disaster Resistant Design of Structures’
  2. 2. • Part 6 Structural Design Structural Safety – 7 Sections – 438 pages – almost half the NBC
  3. 3. Part 6 Structural Design • Section 1 Loads, Forces and Effects • Section 2 Soils and Foundations • Section 3 Timber and Bamboo 3A Timber 3B Bamboo • Section 4 Masonry
  4. 4. Part 6 Structural Design contd… • Section 5 Concrete 5A Plain and Reinforced Concrete 5B Prestressed Concrete • Section 6 Steel • Section 7 Prefabrication, Systems Buildings and Mixed/Composite Construction 7A Pre-fabricated concrete 7B Systems Buildings and Mixed/Composite Construction
  5. 5. IS 875 Code • IS 875 Code of practice for design loads (other than earthquake) for buildings and structures; Part 2 : 1987 Imposed loads (second revision) Part 3 : 1988 Wind loads (second revision) Part 4 : 1987 Snow loads (second revision) Part 5 : Special loads and load combination (second revision)
  6. 6. IS 875 Code • Also refer to SP 64 (S&T) :2001 ‘ Explanatory Handbook on Indian Standard code of practice for design loads (other than earthquake) for buildings and structures : Part 3 Wind Loads
  7. 7. Section 1 Loads, Forces and Effects • Revised Standard IS 1893 (Part 1) – 2002 ‘Criteria for Earthquake resistant design of structures: Part 1 General provisions and Buildings (fifth revision)’
  8. 8. Imposed loads • Residential Buildings • Educational buildings • Institutional Buildings • Assembly Buildings • Business and Office Buildings • Mercantile buildings • Industrial Buildings • Storage Buildings
  9. 9. Imposed loads • Label indicating Designed Imposed Loading to be displayed at a conspicuous place. – Distributed Load kN/m2 – Concentrated Load kN
  10. 10. Wind Load • Equivalent static load for steady wind load is ok for short and heavy structures • Gust factor method considering drag on structures for flexible structures • In case of tall structures with unsymmetrical geometry designs are to be checked for torsional effects
  11. 11. Wind Load • Depends on – risk level – terrain roughness, height and size of structure – local topography
  12. 12. Wind Load • Basic wind speed Map( based on 50 year return period from code
  13. 13. Wind & Cyclone Map of India
  14. 14. TOO SMALL FOR LIGHT WEIGHT BUILDING, PULLED COMPLETELY OUT OF THE GROUND FOUNDATIONS
  15. 15. Dramatic & Total Destruction Of Large, Steel, Portal Frame Building STEEL FRAMES
  16. 16. LOSS OF CORRUGATED, METAL, ROOF SHEETS ROOF SHEETING
  17. 17. COLLAPSED LATTICE TOWERS TELECOMMUNICATION TOWERS & MASTS
  18. 18. Wind Load • Design wind speed Vz = Vb k1 k2 k3 – Vz = design wind speed at any height z in m/s – Vb = basic wind speed in m/s – k1 = probability factor (risk coefficient) Table 4 – k2 = terrain, height and structure size factor – k3 = topography factor
  19. 19. Wind Load • Design wind pressure pz = 0.6 Vz 2
  20. 20. Wind Load • Pressure Coefficients Cp code gives tables for various types and shapes of buildings
  21. 21. Seismic load • IS 1893 : 2002 ‘
  22. 22. Lack of shear connection between floors and the elevator shaft 5 storey R.C., collapse of open plinth, water tank at top dislocated (Bhuj)
  23. 23. Identical 4 storeyed R.C. buildings (Amdavad) two out of four collapsed Collapse of R.C. frame railway station building at Vondh
  24. 24. Soft ground storey collapse (Amdavad) Pancake collapse of a R.C. Building (Gandhidham)
  25. 25. Elevator shaft - weak shear connections with floors (Amdavad) Infill wall damage
  26. 26. BIS Standards • IS 1893-2002 : Criteria for earthquake resistant design of structures • IS4326-1993 : Earthquake Resistant Design and construction for buildings – code of practice (second revision) • IS 13920-1993 : Ductile detailing of RC structures subjected to seismic forces – code of practice
  27. 27. VARIOUS PARTS OF IS 1893:2002 • Part 1: General provisions and buildings • Part 2: Liquid retaining tanks - Elevated and ground supported • Part 3: Bridges and retaining walls • Part 4: Industrial structures including stack like structures • Part 5 : Dams and embankments
  28. 28. Important Modifications • Design Basis Earthquake (DBE) E/Q that can reasonably be expected to occur once during the design life of the structure • Maximum Considered Earthquake (MCE) The most severe earthquake effects considered by this standard
  29. 29. Assumptions • Generally designed for earthquake coming from one direction at a time • Resonance will not occur • Earthquake will not occur with extreme wind
  30. 30. Performance criteria • Moderate Earthquake – Without structural damage – Could occur a number of times in the life span – Code based design seismic coefficients • Large earthquake – Without collapse – May occur once in the life of the structure – Not catered by the codal design seismic co- efficient – Additional resistant by incorporating details for ductility
  31. 31. Zoning Map • Zone I and II of the contemporary map has been merged and assigned the level of Zone II • Khillari area has been included in Zone III • The parts of eastern coast areas, the level of Zone II has been enhanced to Zone III
  32. 32. Seismic Zone Factors • Maximum Considered Earthquake(MCE) – The most severe earthquake effects considered by this standard • Zone Factor (Z) – It is a factor to obtain the design spectrum depending on the perceived maximum seismic risk characterized by MCE in the zone in which the structure is located. – The basic zone factors included in this standard are reasonable estimate of effective peak ground acceleration Seismic Zone II III IV V Factor 0.1 0.16 0.24 0.36
  33. 33. DESIGN HORIZONTAL LOAD • When lateral resisting elements are orthogonal, consider e/q load in one direction at a time. • When non-orthogonal – Combine full load in one direction with 30% of load in other direction EL in load combination replaced by ELx±0.3ELy or 0.3ELx±ELy
  34. 34. Response reduction factor (R) • It is the factor by which the actual base shear force, shall be reduced to obtain the design lateral force. – Actual base shear force - that would be generated if the structure were to remain elastic during its response to the Design Basis Earthquake (DBE) shaking. – The values of ‘R’ depend upon seismic damage performance of the structure, i.e. ductile/brittle. • Design Basis Earthquake (DBE) – It is the earthquake which can reasonably be expected to occur at least once during the design life of the structure. – Z / 2
  35. 35. Response Reduction Factor(R) Ordinary RC moment-resisting frame(OMRF) 3.0 Special RC moment-resisting frame(SMRF) 5.0 Load bearing masonry wall buildings a) Un-reinforced 1.5 b) Reinforced with horizontal RC bands 2.5 c) Reinforced with horizontal RC bands and vertical bars at corners of rooms and jambs of openings 3.0 Ordinary reinforced concrete shear walls 3.0 Ductile shear walls 4.0 Ordinary shear wall with OMRF 3.0 Ordinary shear wall with SMRF 4.0 Ductile shear wall with OMRF 4.5 Ductile shear wall with SMRF 5.0 Lateral Load Resisting System R
  36. 36. Design Lateral Force Revised • Design Seismic Base Shear (VB ) (Lower Bound) VB = Ah W Where, Ah = Design horizontal acceleration spectrum using the approximate fundamental natural period Ta (Clause 7.6) in the considered direction of vibration; and W = Seismic weight of the building
  37. 37. Design horizontal seismic coefficient Ah) • Z = Zone factor given in Table 2, is for the MCE and service life of structure in a zone. The factor 2 in the denominator of Z is used so as to reduce the MCE zone factor to the factor for DBE. • I = Importance factor (Table 6) • R = Response reduction factor (Table 7) I/R shall not be greater than 1.0 • Sa / g = Average response acceleration coefficient. gR SIZ A a h 2 =
  38. 38. Response Spectra 1. 0 3.0 2.0 1.0 2.0 3.0 4.0 Type III (Soft soil) Type II (Medium soil) Type I (Rock, or Hard soil) Period SpectralAccelerationCoefficient(Sa/g)
  39. 39. Fundamental Natural Period RC frame building • Moment-resisting frame building without brick infill panels Ta = 0.075 h0.75 [Old version, Ta = 0.1N(No. of storey) , No mention about the brick infill panel] • Moment-resisting frame buildings with brick infill panel where, h = Height of building and d = Base dimension of the building at the plinth level, in m, along with considered direction of the lateral force. d h aT 09.0=
  40. 40. Attributes to perform well in a earthquake • Simple and regular configuration • Adequate lateral strength • Adequate stiffness • Adequate ductility
  41. 41. Regular and Irregular Configuration • Buildings having simple regular configuration suffer less damage than buildings with irregular configuration. • Regular Configuration – Simple regular geometry – Uniformly distributed mass and stiffness in plan and elevation • Irregular configuration – As defined in Table 4 and 5 of the code
  42. 42. Plan and Vertical Irregularities
  43. 43. Plan Irregularities • Torsion Irregularity • Re-entrant Corners • Diaphragm Discontinuity • Out-of-plane offsets • Non-parallel systems
  44. 44. Plan Irregularities (Table 4) • Tortional Irregularity – To be considered when floor diaphragms are rigid in their own plan – when the maximum storey drift, computed with design eccentricity, at one end of the structure transverse to an axis is more than 1.2 times the average of the storey drifts at the two ends of the structure. { ∆2 =1. 2 (∆1 + ∆2) / 2} ∆ 1 ∆ 2
  45. 45. Plan Irregularities (Table 4) …Contd. • Re-entrant Corners, – where both projections of the structure beyond the re-entrant corner are greater than 15 percent of its plan dimension in the given direction. A1<0.15L1, A2<0.15L2 Contd… L1 L2 A1 A2
  46. 46. Plan Irregularities (Table 4) …Contd. • Diaphragm Discontinuity – Diaphragms with abrupt discontinuities or variations in stiffness: • those having cut-out or open areas greater then 50 percent of the gross enclosed diaphragm area • or changes in effective diaphragm stiffness of more than 50 percent from one storey to the next. Contd…
  47. 47. Plan Irregularities (Table 4) …Contd. • Out-of-Plan Offsets – Discontinuities in a lateral force resistance path, such as out-of plan offsets of vertical elements. Position of shear wall Ground Floor Plan First Floor Plan
  48. 48. Plan Irregularities (Table 4) …Contd. Non-Parallel Systems – The vertical elements resisting the lateral force are not parallel to or symmetric about the major orthogonal axes or the lateral force resisting elements. X Y
  49. 49. Vertical Irregularities • Stiffness irregularity – soft storey • Mass irregularity • Geometric irregularity • In-plane discontinuity • Discontinuity in capacity – weak storey
  50. 50. Vertical Irregularities (Table 5) • Stiffness irregularity – Soft Storey – A soft storey is one in which the lateral stiffness is less than 70 percent of that in the storey – or less than 80 percent of the average lateral stiffness of the three storeys above. • Stiffness irregularity – Extreme Soft Storey – A extreme soft storey is one in which the lateral stiffness is less than 60 percent of that in the storey above – or less than 70 percent of the average stiffness of the three storeys above, e.g., buildings on STILTS will fall under this category.
  51. 51. Vertical Irregularities (Table 5) …Contd. • Mass Irregularity – Mass irregularity shall be considered to exist where the seismic weight of any storey is more than 200 percent of that of its adjacent storeys. – The irregularity need not be considered in case of roofs. • Vertical Geometric Irregularity – Vertical geometric irregularity shall be considered to exist where the horizontal dimension of the lateral force resisting system in any storey is more than 150 percent of that in its adjacent storey. Contd…
  52. 52. Vertical Irregularities (Table 5) …Contd. • In-Plane Discontinuity in Vertical Elements Resisting Lateral Force – A in-plane offset of the lateral force resisting elements greater than the length of those elements. • Discontinuity in Capacity – Weak Storey – A weak storey is one in which the storey lateral strength is less than 80 percent of that in the storey above. – The storey lateral strength is the total strength of all seismic force resisting elements sharing the storey shear in the considered direction.
  53. 53. Dynamic Analysis • Regular Buildings – Those greater than 40 m in height in Zones IV & V, – Those greater than 90 m in height in Zones II and III. – Modeling as per 7.8.4.5 can be used for response spectrum method. • Irregular Buildings – All framed buildings higher than 12 m in Zones IV & V, – Those greater than 40 m in height in Zones II and III. – The analytical model for dynamic analysis of buildings with unusual configuration should be such that it adequately models the types of irregularities present in the building configuration. – Buildings with plan irregularities, as defined in Table 4 (as per 7.1), cannot be modeled for dynamic analysis by the method given in 7.8.4.5. • At least 3 degree of freedom are to be considered for each floor
  54. 54. Buildings with Soft Storey *Buildings with a flexible storey, – such as the ground storey consisting of open spaces for parking that is Stilt buildings, – special arrangements needs to be made to increase the lateral strength and stiffness of the soft/open storey. • Dynamic analysis of building is carried out including – the strength and stiffness effects of infill and – inelastic deformations in the members particularly, those in the soft storey, and the members designed accordingly. Contd….
  55. 55. Buildings with Soft Storey …contd. • Alternatively, – Carrying out the earthquake analysis, neglecting the effect of infill walls in other storeys. – The columns and beams of the soft storey are to be designed for 2.5 times the storey shears and moments calculated under seismic loads specified in the other relevant clauses; or – Besides the columns designed and detailed for the calculated storey shears and moments, shear walls placed symmetrically in both directions of the building as feasible; to be designed exclusively for 1.5 times the lateral storey shear force calculated as before.
  56. 56. Need for ductility • Earthquake resistant design – costs money • Cost increases geometrically for no damage design • Codes adopts lower coefficient – reduction factor • Provisions for durability for once in life earthquake • Design criteria is no-collapse design • IS-13920 – 1993 detailing for ductility
  57. 57. Roof-top DisplacementRoof-top Displacement V/W(Acceleration)V/W(Acceleration) Low-Strength; Low-Stiffness; BrittleLow-Strength; Low-Stiffness; Brittle Moderate Strength and Stiffness; DuctileModerate Strength and Stiffness; Ductile High-Strength; High-Stiffness; BrittleHigh-Strength; High-Stiffness; Brittle
  58. 58. Principles of ductility • Avoid shear failure • Avoid compression failure • Ensure continuity • Confine the critical areas where hinge can form.
  59. 59. Snow load • s = μ s0 s = design snow load in N/m2 μ = shape coefficient s0 = Ground snow load
  60. 60. Special Loads • Temperature Effects • Hydrostatic & soil Pressure • Fatigue • Structural Safety during construction • Accidental loads • Vibrations
  61. 61. Load Combinations • Various loads are to be combined to evaluate the most unfavourable effect • Simultaneous occurrence of maximum values of wind, earthquake, imposed and snow load is not likely
  62. 62. Multi – Hazard Risk • Earthquake • Cyclones • Windstorm • Floods • Landslides • Liquefaction of soils • Extreme winds • Cloud bursts • Failure of slopes
  63. 63. DISASTER MANAGEMENT CYCLE Emergency Response Post-disaster: recovery Preparedness Prevention/ Mitigation Reconstruction Rehabilitation Response/Relief Pre-disaster: risk reduction Disaster Emergency Response Post-disaster: recovery Preparedness Prevention/ Mitigation Reconstruction Rehabilitation Response/Relief Pre-disaster: risk reduction Disaster
  64. 64. Multi – Hazard Risk • Code gives criteria for identifying the multi- hazard districts and a list of such districts is at Ann: M
  65. 65. Vulnerability Atlas of India, 1987 • Seismic hazard map • Cyclone and wind map • Flood prone area map • Housing stock vulnerability table
  66. 66. Vulnerability Atlas of India, 1987 • Landslide Hazard Zonation Atlas, 2003 BMTPC
  67. 67. Hazard Maps The earthquake , wind storm and flood hazard maps are drawn for each state and Union Territory separately in which various district boundaries are clearly shown for easy identification of the hazard prone areas.
  68. 68. The Vulnerability Atlas of India The Vulnerability Atlas of India has been structured to serve as a tool towards natural disaster prevention , preparedness and mitigation for housing and related infrastructure at local as well as national levels.
  69. 69. Hazard Maps The earthquake , wind storm and flood hazard maps are drawn for each state and Union Territory separately in which various district boundaries are clearly shown for easy identification of the hazard prone areas.
  70. 70. Flood Hazard Map of India
  71. 71. LANDSLIDE HAZARD MAP OF INDIA
  72. 72. EARTHQUAKE HAZARD MAP OF GUJARAT
  73. 73. FLOOD HAZARD MAP OF GUJARAT
  74. 74. WIND & CYCLONE HAZARD MAP OF GUJARAT
  75. 75. TABLE 1 – BUILDING TYPES IN FIVE DISTRICTS OF GUJARAT Wall Type No. of Houses and percentage of Total in District Kachchh % Jamnagar % Banaskanth a (incl. Patan) % Rajkot % Surendranagar % Category A 276,390 70.72 215,135 52.04 268,790 54.90 295,005 46.81 281,475 85.04 Category B 56,995 14.58 183,050 44.28 202,185 41.29 310,925 49.34 43,705 13.20 Category C 42,135 10.78 9,980 2.41 6,705 1.37 15,15 2.46 2,870 0.87 Category X 15,290 3.91 5,210 1.26 11,955 2.44 8,760 1.39 2,9 0.89 Total 390,810 100 413,375 100 489,635 100 630,205 100 330,995 100 Source: Vulnerability Atlas of India, 1997 Category A - Building in field-stone, rural structures, unburnt brick houses, clay houses Category B - Ordinary brick buildings; buildings of the large block and prefabricated type, half-timbered structures, buildings in natural hewn stone Category C - Reinforced building, well built wooden structures Category X - Other types not covered in A,B,C. as of biomass, metal sheets etc. These are generally light.
  76. 76. GUJARAT – EARTHQUAKE DAMAGE TO BUILDINGS (100 YEARS RETURN PERIOD) (Number of Buildings)
  77. 77. ESTIMATED PROBABLE MAXIMUM SURGE AT MEAN SEA LEVEL
  78. 78. MAH INSTALLATIONS - ALL CHEMICAL HAZARDS
  79. 79. Section 2 Soils and Foundations • 1080: 1985 Design and construction of shallow foundations in soils ( other than raft, ring and shell) (second revision) • 1904: 1986 Design and construction foundations in soils : General requirements (third revision)
  80. 80. Section 2 Soils and Foundations contd…. • 2911 (part 1/sec 1): 1979 Design and construction of pile foundations: Part 1 Driven cast in situ concrete piles) • 2911 (part 1/section 2): 1979 Bored cast in situ concrete piles • 2911 (Part 1/section 3): 1979 Driven precast concrete piles • 2911 (Part 1/section 4): 1984 Bored precast concrete piles • 2911 Part 3): 1980 Under-reamed piles (first revision
  81. 81. Section 2 Soils and Foundations contd • 2950(Part 1): 1981 Raft foundations • 9456: 1980 Conical hyperbolic paraboloidal types of shell foundations
  82. 82. Section 2 Soils and Foundations contd • Site Investigations • Shallow foundations • Allowable bearing Pressure • Safe bearing capacity based on shear strength • Based on allowable settlement • Depth of foundations • On soils min 500 mm
  83. 83. Section 3 Timber and Bamboo
  84. 84. Timber Codes • 399: 1963 Classification of commercial timbers and their zonal distribution (revised) • 883: 1994 design of structural timber in buildings • 1150: 2000 Trade names and abbreviated symbols foe timber species (third revision) • 2366: 1983 Nail-jointed timber construction (first revision)
  85. 85. Timber • 4891: 1988 specification for preferred cut sizes of structural timber (first revision) • 4983: 1968 design and construction of nailed laminated timber beams • 11096: 1984 design and construction of bolt- jointed timber construction • 14616: 1999 specification for laminated veneer lumber
  86. 86. Bamboo Codes • 6874: 1973 Method of test for round bamboo • 8242: 1976 Method of test for split bamboo • 9096: 1979 Preservation of bamboo for structural purposes • 13958: 1994 specification for bamboo mat for general purposes
  87. 87. Masonry Codes • 1905: 1987 Structural use of unreinforced masonry (third revision) • 4326: 1993 Earthquake resistant design and construction of buildings • Sp 20: 1991 Handbook on masonry design and construction (first revision)
  88. 88. Masonry Changes • Special consideration for earthquakes brought in line with IS 4326 • New clause on guidelines for improving earthquake resistance of low strength masonry buildings added • Reference to design and of reinforced brick concrete floors and roofs has been included
  89. 89. • I S 1905- 1987 : Code of Practice for Structural Use of Un-reinforced Masonry • SP 20: Handbook on Masonry Design and Construction
  90. 90. IS 1905 Cl. 0.6 Assumes that : Design is carried out by qualified Engineer
  91. 91. 1905 is applicable for • Un-reinforced load bearing wall •Non-load bearing wall Constructed with: - Solid or perforated burnt clay bricks IS 1077 (Common burnt clay) or IS 2180 (Heavy duty burnt clay) or IS 2222 (Burnt clay perforated) - Sand lime bricks IS 4139-1976 - Stones IS 3316(Structural granite) or IS 3620(Laterite block)
  92. 92. 1905 is applicable for contd.. • Concrete blocks IS 2185 Part 1 Hollow &Solid IS 2185 Part 2 Hollow and solid ( light weight) • Lime based blocks IS 3115 • Burnt clay hollow blocks IS 3952 • Gypsum partition blocks IS 2849 • Autoclaved cellular concrete blocks IS 2185 Part 3 • Walls constructed with mud mortars are not included
  93. 93. Planning • Eccentricity is kept minimum Adequate stiffness of walls Load to be uniformly distributed • For load bearing buildings up to 4 stories, height to width ratio of buildings should not exceed 2 • For halls of length exceeding 8 m, safety and adequacy of lateral supports shall be checked by structural analysis
  94. 94. Mortar Properties Lime is added to improve workability, water retention, and bonding properties Plasticised cement sand mortar Mortar for masonry shall conform to IS 2250
  95. 95. effect of joint thickness on brickwork strength fig 3.2
  96. 96. Method of construction • Stone masonry IS 1597 part 1 • Rubble stone masonry • IS part 2 Ashlars • Brickwork masonry IS 2212 • Hollow concrete block masonry IS 2572
  97. 97. Method of construction contd.. • Autoclaved cellular concrete block masonry: IS 6041 • Light weight concrete block masonry: IS 6042 • Gypsum partition blocks: IS 2849
  98. 98. Guidelines for Approximate Design of Non-load Bearing Wall • Panel walls • Curtain walls • Partition walls
  99. 99. construction of RB and RBC floors and roofs IS 10440 code of practice for construction of RB and RBC floors and roofs
  100. 100. IS 13828: Improving earthquake resistance of low strength masonry buildings guidelines Earthquake Resistance
  101. 101. Earthquake Resistance IS 4326: Code of Practice for Earthquake Resistant Design and Construction of Structures
  102. 102. Table: 2 BUILDING CATEGORIES FOR EARTHQUAKE RESISTING FEATURES (Clause 7.1.1) Building Range of αh Categories A 0.04 to less than 0.05 B 0.05 to 0.06 (both inclusive) C More than 0.06 and less than 0.08 D 0.06 to less than 0.12 E Equal to or more than 0.12
  103. 103. Table 3 Recommended Mortar Mixes (Clauses 8 1.2.1 and 8.2.6) *Category of Proportion of Cement Construction Lime-Sand† A M2 (Cement-sand 1:6) or M3 (Lime- cinder‡ 1:3) or richer B,C M2 (Cement-lime-sand) 1:2:9 or Cement-Sand 1:6) or richer D,E H2 (Cement-sand 1:4) or M1 (Cement- lime-Sand 1:1:6) or richer
  104. 104. Table 4 SIZE AND POSITION OF OPENINGS IN BEARING WALLS (Clause 8.3.1 and Fig.7) Sl. Position of Pening Details of Opening for Building Category No. 1. Distance b5 from the inside corner of A and B C D and E outside wall, Min Zero mm 230 mm 450 mm 2. For total length of openings, the ratio (b1+b2+b3)/11 or (b6+b7)/12 shall not exceed: a) one-storeyed building 0.60 0.55 0.50 b) two-storeyed building 0.50 0.46 0.42 c) 3 or 4-storeyed building 0.42 0.37 0.33 3. Pier width between consecutive open- 340 mm 450 mm 560 mm ning b4, Min
  105. 105. Fig.7 Dimensions of Openings and Pipes for Recommendations in Table 4
  106. 106. Table 5 STRENTHENING ARRANGIEMENTS RECOMMENDED FOR MASONARY BUILDINGS (Rectangular Masonry Units) Building Number of Strengthening to Category Storeyes be Provided in all Storeyes A i) 1 to 3 a ii) 4 a, b, c B i) 1 to 3 a,b,c,f,g ii) 4 a,b,c,d,f,g C i) 1 and 2 a,b,c,f,g ii) 3 and 4 a to g D i) 1 and 2 a to g ii) 3 and 4 a to h E 1 to 3* a to h
  107. 107. Table 5 (Contd…) Where a Masonry mortar (See 8.1.2) b Lintel band (see 8.4.2) c Roof band and gable band where necessary (see 8.4.3 and 8.4.4), d Vertical steel at corners and junctions of walls (see 8.4.8) e Vertical steel at jambs of openings (see 8.4.9) f Bracing in plan at tie level of roofs (see 5.4.2.2) g Plinth band where necessary (see 8,4,6), and h Dowel bars (see 8.4.7)
  108. 108. Table 6 Recommended Longitudinal Steel in Reinforced Concrete Bands (Clause 8.4.5) Span Building Building Building Building Category Category Category Category B C D E No. Dia No. of Dia No. of Dia No. of Dia of Bars Bars Bars Bars (1) (2) (3) (4) (5) (6) (7) (8) (9) m mm mm mm mm 5 or less 2 8 2 8 2 8 2 10 6 2 8 2 8 2 10 2 12 7 2 8 2 10 2 12 4 10 8 2 10 2 12 4 10 4 12
  109. 109. Cyclone Resistance Guidelines for Improving Cyclone Resistance of Houses/Buildings
  110. 110. Section 5 concrete
  111. 111. IS : 456 • 1st Revision 1953 Working Stress Method • 2nd Revision 1964 Ultimate Load Method • 3rd Revision 1978 Limit State Method • 4th Revision 2000 Durability
  112. 112. 4th Revision Sampling and Acceptance Criteria Types of Cements increased. Mineral admixtures introduced  Fly ash  GGBS  CSF  Rice Husk Ash  Metakaoline
  113. 113. 4th Revision  Higher strength concrete  Exposure condition  Minimum requirements for durability  Quality Assurance, Inspection  Fire Resistance  Cover/Nominal Cover  Lap Length
  114. 114. TYPES OF CEMENT  33 Grade Ordinary Portland cement conforming to IS 269  43 Grade ordinary Portland cement conforming to IS 8112  53 Grade ordinary Portland cement conforming to IS:12269  Rapid hardening Portland cement conforming to IS:8041  Portland slag cement conforming to IS:455
  115. 115. TYPES OF CEMENT Portland pozzolana cement (fly ash based) conforming to IS:1489 (Part 1) Portland pozzolana cement (calcined clay based) conforming to IS:1489 (Part 2). Hydrophobic cement conforming to IS:8043 Low heat Portland cement conforming to IS:12600. Sulphate resisting Portland cement conforming to IS:12330.
  116. 116. TABLE 1 PERMISSIBLE LIMIT FOR SOLIDS (Clause 5.4)Tested as per Permissible Limit Max. Organic IS 3025 (Pt 18) 200 mg/1 Inorganic IS 3025 (Pt 18) 3 000 mg/1 Sulphates (as SO3) IS 3025 (Part 24) 400 mg/1 Chlorides (as C1) IS 3025 (Part 32) 2 000 mg/1 for concrete work containing embedded steel and 500 mg/1 for reinforced concrete work Suspended matter IS 3025 (Pt 17) 2 000 mg/1
  117. 117. TABLE 2 : GRADES OF CONCRETE (Clauses 6.1, 6.2.1, 9.2.1, 15.1.1 and 16.1 Group Grade Designa- tion Specified Characteristic Compressive Strength of 150 mm cube at 28 days in N/mm2 1 2 M 10 10 M 15 15 Ordinary Concrete M 20 20 M 25 25 M 30 30 Standard Concrete M 35 35
  118. 118. GRADES OF CONCRETE M 35 35 M 40 40 M 45 45 M 50 50 M 55 55 M 60 60 M 65 65 M 70 70 M 80 75 High Strength Concrete 80
  119. 119. CONCRETE MIX • Concrete of compressive strength less than M20 may be used for plain concrete constructions, lean concrete, simple foundations, foundation for masonry walls and other simple or temporary construction.
  120. 120. MODULUS OF ELASTICITY • Modulus of Elasticity of concrete 5 000 √fck
  121. 121. HOLISTIC APPROACH TO DURABILITY • Selection of Site • Structural designs and detailing • Concrete technology • System of construction • Drainage, cover, water proofing • Inspection, maintenance & repair
  122. 122. FACTORS AFFECTING DURABILITY  the environment  the cover to embedded steel  the type and quality of constituent material  the cement content and water/cement ratio of the concrete  workmanship, to obtain full compaction and efficient curing  the shape and size of the member.
  123. 123. TABLE 3 : ENVIRONMENTAL EXPOSURE CONDITIONS (Clause 8.2.2.1) Environment Exposure Conditions Mild Concrete surfaces protected against weather or aggressive conditions except those situated in coastal area. Moderate Concrete surfaces sheltered from seven rain or freezing whilst wet Concrete exposed to condensation and rain Concrete continuously under water Concrete in contact or buried under non-aggressive soil/ground water
  124. 124. ENVIRONMENTAL EXPOSURE CONDITIONS Severe Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation. Concrete completely immersed in sea water Very severe Concrete exposed to coastal environment Concrete surfaces exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet. Concrete in contact with or buried under aggressive subsoil/ground water. Extreme Surface of members in tidal zone. Members in direct contact with liquid/solid aggressive chemicals.
  125. 125. TABLE 5 : MINIMUM CEMENT CONTENTS, MAXIMUM W/C RATION AND MINIMUM GRADE OF CONCRETE FOR DIFFERENT EXPOSURE WITH NORMAL WEIGHT AGGREGATES OF 20 MM NOMINAL MAXIMUM SIZE. Exposure Plain Concrete Reinforced Concrete Minimum Grade of Concrete Mini. Cement content Kg/m3 Max. Free w/c Mini. Cement content Kg/m3 Max. Free w/c Plain Concrete Reinforced Concrete Mild 220 0.60 300 0.55 - M20 Moderate 250 0.60 300 0.50 M15 M25 Severe 260 0.50 350 0.45 M20 M30 Very Severe 280 0.45 375 0.45 M20 M35 Extreme 300 0.40 375 0.40 M25 M40
  126. 126. MAXIMUM CEMENT CONTENT • Maximum Cement Content 450 Kg/m3
  127. 127. NOMINAL COVER TO MEET DURABILITY REQUIREMENTS Exposure Nominal Concrete Cover in mm Not less than Mild 20 Moderate 30 Severe 45 Very Severe 50 Extreme 75 Notes: i. For main reinforcement up to 12 mm diameter bar for mild exposure the nominal cover may be reduced by 5 mm ii. Unless specified otherwise, actual concrete cover should not deviate from the required nominal cover by +10 mm or 0mm.
  128. 128. DETAILING • Corner of a section and the minimum cover to either face is less than twice the diameter of the lapped bar or where the clear distance between adjacent laps is less than 75 mm or 6 times the diameter of lapped bar, whichever is greater, the lap length should be increased by a factor of 1.4. • Where both condition (i) and (ii) apply, the lap length should be increased by a factor of 2.0.
  129. 129. BATCHING Ready mix concrete supplied by RMC plant shall be preferred. Accuracy of equipment  2% for cement  3% for aggregate, admixture, water.
  130. 130. 5b Prestressed concrete • IS 1343: 1980 code of Practice for Prestressed concrete (first revision) • • Under revision to be incorporated when ready..
  131. 131. CONCRETE CORBELS NEW CLAUSE 28.1 General • A corbel is a short cantilever projection which supports a load bearing member and where: a) the distance a between the line of the reaction to the supported load and the root of the corbel is less than d (the effective depth of the root of the corbel); and
  132. 132. CONCRETE CORBELS NEW CLAUSE b) the depth at the outer edge of the contact area of the supported load is not less than one-half of the depth at the root of the corbel. The depth of the corbel at the face of the support is determined from shear consideration in accordance with 40.5.2 but using the modified definition of av given in (a).
  133. 133. WALLS • Steel to be provided on both faces • Min. thickness shall be 100mm • Clause 32.2 method for vertical load only • Clause 32.3 method for combined Vertical & Horizontal forces.
  134. 134. 21. FIRE RESISTANCE Durability removed ( & made into a new Chapter.) IS:1641 for fire resistance in hrs. – Member size – Detailing – Cover – Types of aggregate IS:1642 for Fire Protection
  135. 135. MIN. REQUIREMENTS • Min requirement – Fig.1 & Table of Fig.1 • Special provision when cover exceeds 40mm • Clause 26.4.3. cover for fire resistance. Table 16.
  136. 136. FIRE RESISTANCE Nominal cover Beams Floors Ribs Column Fire resist- tance hrs. Simply supported Continuous Simply supported continuous Simply supported Continuous 0.5 20 20 20 20 20 20 40 1 20 20 20 20 20 20 40 1.5 20 20 25 20 35 20 40 2 40 30 35 25 45 35 40 3 60 40 45 35 55 45 40 4 70 50 55 45 65 55 40
  137. 137. FIRE RESISTANCE
  138. 138. FIRE RESISTANCE Column dimension (b or D) Minimum wall thicknessFire resista nce h Min. beam width b Rib width bw Min. thickne ss of floors D Fully expose d 50% expose d One face expose d P<0.4 % 0.4%< p <1% >1% Hrs. mm mm mm mm mm mm mm mm mm 0.5 200 125 75 150 125 100 150 100 100 1 200 125 95 200 160 120 150 120 100 1.5 200 125 110 250 200 140 175 140 100 2 200 125 125 300 200 160 - 160 100 3 240 150 150 400 300 200 - 200 150 4 280 175 170 450 350 240 - 240 180
  139. 139. Section 6 Steel • IS 800 : 1984 Code of practice for general construction in steel (second revision) • IS 806: 1968 code of practice for use of steel tubes in general building construction (first revision)
  140. 140. • IS 800 is undergoing revision • Introduction of limit state design • Plastic range of material for design of structural members • Ultimate limit state and serviceability limit state • Incorporatea load factors • Tension and compression have different performance factors • Critical buckling stress considering local buckling of members classified as slender, semi- compact, compact and Plastic.
  141. 141. • Section 7 • Prefabrication systems Buildings • And mixed /composite Construction • 7A Prefabricated Concrete
  142. 142. 7A Prefabricated Concrete • Importance aesthetics highlighted • Clauses on materials added • Clauses on prefabrication systems and structural elements elaborated • Clauses on testing of components revised • Manufacture of cellular concrete added
  143. 143. 7A Prefabricated Concrete • Modular coordination and modular dimension of components revised bring about more flexibility in planning • Provisions for tolerance revised to include different types of prefabricated components • Detailed clause on safety requirements against progressive collapse added
  144. 144. Systems Buildings and Mixed/composite Construction • Prescribes general requirements applicable to all valid existing systems and mixed/composite constructions • Flexibility to accommodate new systems introduced in future is also incorporated
  145. 145. Jose Kurian Chief Engineer, DTTDC

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