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BMC Unit 4

complete notes of unit 4 in bmc according jntuk r13 2-1 syllabus

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BMC Unit 4

  1. 1. UNIT. IV:BUILDING COMPONENTS Prepared by:K.SAHITYA, Asst prof. Civil engineering dept. BVC college,odalarevu Lintels, arches, vaults, stair cases – types. Different types of floors – Concrete, Mosaic, Terrazzo floors, Pitched, flat roofs. Lean to roof, Coupled Roofs. Trussed roofs – King and Queen post Trusses. R.C.C Roofs, Madras Terrace and Pre fabricated roofs. Lintels: Lintel isa horizantal memberwhichisfixedover The openings such as doors,windows..etc to support the structure or opening  They Provides bearing for the masonry above openings  They can Transfer loads acting over the opening to the supporting walls Types of lintels Stone lintels wooden lintels Brick lintels Steel lintels Reinforced concrete lintels Reinforced brick lintels Stone lintels:  These are generally used in stone masonry  High cost  Having inablity to withstand excessive transverse stresses so rarely used  minimum thickness is 8 cm
  2. 2. wooden lintels  These are very commonly used inolden days  But now a days timber availability became difficult and costly too,so not used in these days  Easily effected by white ants and insects  Not fire proof  minimum thickness is 7.5 cm  Weak when compared with other types of lintels Brick lintels  These are generally used for small openings(<1 mt) with light loading  Bricks with frogs (i.e, depressions) are more suitable.  Lintels formed by using frog bricks is termed as joggled brick lintel  Bricks should hard,well burnt free from defects with sharp and square edges  thickness is 10 cm,20 cm…etc depends upon opening size As it is weak not suitable for heavy loadings Steel lintels  These are generally used in the form of rolled steel joists  Formers can be used for small spans and light loadings  Latter can be used for large spans and heavy loadings  These are generally provided where there is less space to construct rise of an arch.  The steel collapses quick due to fire and hence the casing of concrete should be provided which makes the steel more fire resistent Reinforced concrete lintels  More durable,strength,fire resisting properties  Economical and easy in construction.  Used for larger spans and heavy loading
  3. 3.  These are constructed with ratio of 1:2:4  Upto 1.2 mt length of span 15 cm deep lintel is found to be safe  as a general rule,add 25 mm for every additions 30 cm span. Reinforced brick lintels  When brick linels used for large spans ,they are reinforced with steel bars.those are called as r.b. lintels  These are also constructed on the same principles as r.c.c lintels,the only difference is instead of using concrete we are using good quality bricks  Bricks arranged in parallel rows that a 2 cm or 4 cm wide space is left length wise for inserting steel bars or rods  These spaces are then filled with rich cement mortar . Arches: The various technical terms used in arches are as follows:-
  4. 4. 1)Abutment:-This is the end support of an arches. 2)Pier:-This is support an intermediate of an arch. 3)Intrados :-This is the inner curve or surface of an arch. 4)Extrados :-This is the outer curve or surface of the arches. 5)Voussoirs :-The voussoirs or arch stones are the wedge shaped units forming the arch. 6)Springing stone:-The springing stone or springer is the first voussoir at springing level on either side of the arches. 7)Springing line:-This is an imaginary line joining the two springing points. 8)Crown:-This is the highest point of extrados or it is the highest part of an arches. 9)Keystone:-This is the highest central wedge shaped block of an arch. 10)Skew back:-This the surface of the abutment on which the arch rests. 11)Span:-This is the clear horizontal distance between the two supports. 12)Rise:-this is the vertical distance between the two supports. 13)Depth of arch:-This is the perpendicular distance between the intrados and extrados. 14)Haunch of an arch:-This is the portion of arch situated centrally between the key and skew backs. 15)Spandril:-This is the triangular walling enclosed by the extrados of the arch, a horizontal line from the crown of the arch and perpendicular line from the springing of the outer curves. An arch may be classified according to their: a)Material of construction and workmanship b)Shape of curve formed by their soffit or intrados c)Number of centers. Classification based on a)Material of construction and workmanship  BRICK ARCHES Rough brick arches
  5. 5.  These arches are built with ordinary bricks, which are not in wedge shape .  Also known as “RELIEVING ARCHES”.  Made up of rectangular brick that are not cut into wedge shape. Curvature are obtained by mortar Axed brick arches  Bricks are cut to wedge-shape.  Joints of arches are of uniform thickness.  Not dress finely so it does not give much attractive appearance. Gauged brick arches  Accurately prepared to wedge shape.  Specially shaped bricks known as “RUBBER BRICKS” are used .  The lime putty is used for binding the blocks  STONE ARCHES Rubble arches  Made of rubble stones, which are hammer dressed, roughly to the shape and size of voussoirs of the arch and fixed in cement mortar.  These arches are used for small span upto 1 m. Ashlar arches  Stones are cut to proper shape of voussoirs and are fully dressed, properly joint with cement or lime.  The voussoirs made of full thickness of the arch.  GAUGED ARCHES Precast concrete block arches  Used for small openings in building.  The voussoirs, in the form of cement concrete blocks are prepared in special moulds  Generally , the concrete blocks are used without reinforcement.
  6. 6. Monolithic concrete arches  Constructed from cast-in-situ concrete ,either plain or reinforced , depending upon the span and magnitude of loading.  Quit suitable for larger span (3.0 m).  The curing is done 2 to 4 weeks. Classification based on shape  Flat arch  Acts like a lintel, when it provided over the opening .  Joints radiated to center.  Used only for light loads only.  Span up to 1.50 m.  Segmental arch  Segmental in shape and provided over the openings .  Joints radiate from a center of arch, which lies below the springing line.  Provided over lintel
  7. 7.  Semi-circular arch  The shape of the curve given to the arch soffit is semi-circular.  The center of the arch lies on the springing line.  Relieving arch  When wooden lintel is provided over the wider opening, a brick relieving arch is constructed above the lintel.  Relieving the load of masonry over lintel.
  8. 8.  Dutch or French arch  Similar to the flat arch in design, but differs in shape and method of construction.  Suitable for small opening.
  9. 9. Classification based on number of centers  One centred arch.  Segmental, semi circular, flat arches come under this category.  Sometime , a perfectly circular arch known as bull’s eye arch ,provided for circular window.  Two centred arch.  Pointed, semi-elliptical arches come under this category.  Three centred arch.  Elliptical arches come under this category.  Four centred arch.  It has four center.  Venetian arch is typical example of this type.  Five centred arch.  This type of arch ,having five centre's ,gives good semi-elliptical shape.
  10. 10. Vaults:  A vault is a ceiling of brick , concrete , Stone , timber , etc built in principle of arch.  A vault, in architecture, is an arch-shaped structure, usually of masonry, used as the ceiling of room or other enclosed space,  as the roof of a building, or as the support for a ceiling or roof.  Masonry vaults are usually composed of wedge-shaped pieces called voussoirs, which are held in  place, like the stones of an arch, by the pressure of the neighboring pieces. Because of the combined  pressure of its components, any arch exerts an outward pressure at its base History of vaults:  In ancient Egypt brick vaulting was used ,chiefly for drains . The Chaldeans and Assyrians used vaults for the same purpose but seem also to have made architectural use of high domes and barrel vaults.  The Greeks made no use of vaults.  Then Rome adopted this technique by using concrete as a construction material so that no outer or external thrust or buttresses need to be given. Thus vaults could be easily erected over vast spaces ,producing impressive and complex thermo , amphitheatres , and basilicas .  The tunnel vault spans between two walls ,like a continuous arch. The cross , or groined , vault is formed by the intersection at right angles of two barrel vaults ,
  11. 11. producing a surface that has arched openings for its four sides and concentration of load at the four corner points of the square or rectangle .  the semicircular arch was universally employed in Romanesque vaulting throughout Europe , and the roman cross vault was the type used for covering square or rectangular compartments. TYPES 0F VAULTS • Barrel vault • Pitched brick barrel vault • Groin vault • Rib vault • Fan vault
  12. 12. BARREL VAULT • Formed by an extension of arch as an unbroken series passed together one behind another. •
  13. 13.  Characteristics • It is known as wagon or tunnel vault. • Circular in shape and semi cylindrical in appearance. • Series of arches placed side by side is known as barrel roof. • It is the simplest form of vault. • It is best for roofing purpose. • Length is greater than a diameter  Materials • Bricks , stone , timber , wood are use generally. • In stone barrel vault due to the problem of fenestration , they provide a small window which restricts the more light and hence for this cloister is used.  STRENGTH • The thrust generated against wall which is its failure. • Solution : 1. Walls should be thick(approx. 4m) and strong. 2 Two or more vaults should be kept parallel to each other. 3. Intersection of two vaults sholud be done at right angle which is known as groin vault. • Butressing should be done. • Uses: church,cloisters,cellars,crypts,hallways,caponier,etc. Types of barrel vault:  Short span barrel vaults  Long span barrel vault  Short span barrel vaults
  14. 14. Short span barrel vaults are those in which span is shorter than its width . It is used for the width of the arch ribs between which the barrel vault span.  Long span barrel vault Long span barrel vaults are those in which span is larger then its width. PITCHED BRICK BARREL VAULT • Bricks are installed vertically ( not radially ) and are leaning at an angle. • Its construction doesn’t reaquire centering
  15. 15.  GROIN VAULT  A Groin vault (also known as a double barrel vault) is produced by the intersection at right angles of two barrel vault.  A cross vault or groined vault (also sometimes known as a double barrel vault or groin vault) is produced by the intersection at right angles of two barrel vaults. The word "groin" refers to the edge between the intersecting vaults.  so the vault need only be abutted at its four corners. STRUCTURE  The construction method was particularly common on the basement level, such as at Myres Castle in Scotland, or at the ground floor level for the storerooms as at Muchalls Castle in Scotland.  accomplish the multiple goals of minimum materials use, wide span of construction, ability to achieve lateral illumination, and avoidance of lateral stresses. Characteristics  The word “groin” refers to the edge between the intersecting vaults.  Sometime the arches of groin vaults are pointed instead of round.  In comparison with a barrel vault, a groin vault provides good economies of material and labour.  The groin vault required great skills in cutting stone to from a neat arris.  Difficult to construct neatly because of the geometry of cross groins.  The construction of groin vault can be understood most simply by visualizing two barrel vault section at right angles merging to form a squarish unit.
  16. 16.  RIB VAULT Definition  The intersection of two or three barrel vaults produces a rib vault or ribbed vault .  Characteristics  when they are edged with an armature of piped masonry often carved in decorative patterns compare groin vault an older from of vault construction.  While the mechanics of the weight of a groin vault and its transmission outwards to the supporting pillars remained as it had been the new use of rib vaults demonstrates the skill of the masons and the grandeu of the new ideas circulating at the introduction of gothic architecture in the end of the eleventh century.  This technique was new in the leta eleventh century for example in the roof of the lchoir side aisles at Durham cathedral.  Ancestors of the gothic rib vault in the Romanesque vault can be found at caen and durham both sites of early gothic constructions and elsewhere.  Some ribbed vaults even have six section in each bay.  TYPES OF RIB VAULT o Rib vaults is reinforced by masonry ribs. o There are two types of rib vault. - Quadripartite rib vault - -Sexpartite rib vault
  17. 17. The vault has two masonry ribs dividing into Lierne vault of the nave of cheste cathedral four sections is called Quadripartite vault  FAN VAULT A fan vault is a form of vault in which the ribs are all of the same curve and spaced equidistantly, in a manner resembling a fan
  18. 18. stair cases stairs: A set of steps leading from surface of a building to another surface, typically inside the building is termed as Stairs.” Function: To protect people from injury and to facilitate access during movement from one level to another in a building Parts of staircase 1. Step : It is a portion of stair which permits ascent & descent. 2. Tread : It is the upper horizontal portion of step upon which the feet is placed. 3. Riser: The vertical portion between each tread on the stair. 4. Handrail : A handrail is a rail that is designed to be grasped by the hand so as to provide stability or support 5. Baluster : It is vertical member of wood or metal supporting the handrail. 6. Newel post : This is the vertical member which is placed at the ends of flights to connect handrail . 7. Run : It is the total length of stairs in a horizontal plane, including landings. 8. Nosing : It is the projecting part of the tread beyond the face of the riser. It is rounded to give good architectural effect.
  19. 19. 9. String Or Stingers : These are the sloping wooden members which support the steps in a stair .They run along the slope of the stair.
  20. 20. Types of staircases: Straight stairs  These are the stairs along which there is no change in direction on any flight between two successive floors. The straight stairs can be of following types.  Straight run with a single flight between floors  Straight run with a series of flight without change in direction  Parallel stairs  Angle stairs  Scissors stairs  Straight stairs can have a change in direction at an intermediate landing. In case of angle stairs, the successive flights are at an angle to each other. Scissor stairs are comprised of a pair of straight runs in opposite directions and are placed on opposite sides of a fire resistive wall. With one flight with2 flights Qurter turn stairs
  21. 21. They are provided when the direction of flight is to be changed by 900. The change in direction can be effected by either introducing a quarter space landing or by providing winders at the junctions Half turn stairs  These stairs change their direction through 1800.  It can be either dog-legged or open newel type.  In case of dog legged stairs the flights are in opposite directions and no space is provided between the flights in plan.  On the other hand in open newel stairs, there is a well or opening between the flights and it may be used to accommodate a lift. These stairs are used at places where sufficient space is available.
  22. 22. Circular stairs  These stairs, when viewed from above, appear to follow circle with a single centre of curvature and large radius. These stairs are generally provided at the rear of a building to give access for servicing at various floors. All the steps radiate from a newel post in the form of winders. These stairs can be constructed in stone, cast iron or R.C.C.
  23. 23. FLOORS  Structural component made to provide a level surface .  It is a horizontal sanitary surface that supports the occupants of a building, furniture and equipment. STRUCTURE OF A FLOOR. The floor is divided into three components Sub base Base concrete Floor finish Concrete flooring  Finish is laid with base concrete on ground.  Topping is laid within 2-3 hours of laying the base concrete  Base concrete imparts strength and have good wearing properties. Base concrete  Consists of 100 mm thick1:4:8 cement concrete  Before placing the base concrete, the sub base should be properly wetted.  Surface should not be finished smooth but kept rough to provide adequate bond for topping. Floor finishing  Topping consist of 1:2:4 cement concrete with a minimum thickness of 25 mm. Topping should be placed in position as soon as possible but not later than 2to 3 hours of laying Mosaic Flooring Flooring is made up of marble chips laid on thin layer of concrete topping. Widely used in school, residential buildings, hospitals, offices and other public buildings
  24. 24. Materials  White cement or grey cement.  Marble chips, size varies from 3mm to 6mm.  Tint of color as desired Preparation  The sub base is prepared in ratio 1:6:12.  It is 3 inch deep  A 30mm deep plain cement concrete is laid in the ratio of 1:2:4. Floor finishing  The finishing layer is of cement and marble dust mixed with marble chips. Cement and marble dust are mixed in ratio of 5:l  cement and marble dust with marble chips, mixed in ratio of 1:2.  Then grinding finishes the floor. Terrazzo floors,  It is the specially prepared concrete surface containing cement and marble chips in proportion to 1:12 to 1:2  The propotion of terrago mix depends on the size of marble chips. But is generally taken 1:2 to 1:3 i.e. one part of cement to two or three pats of marble chips by volume.  The total thickness of terrazo flooring is about 20mm. Colour Pigment to be used Proportion of Pigment Proportion of Cement Proportion of White Cement Red Red oxide of Iron One Unit 60ml 15-20% - Black Carbon Black One Unit 60ml 25-40% - Pink Red Oxide One Unit 60ml - 10%
  25. 25.  The area is divided in to suitable panels of predetermined size and shape  Strips are jointed to base concrete with help of cement mortar  Thickness of strip may be 4 to 6 mm.  Surface of base concrete is cleaned and wetted and then base concrete is laid in alternate panels.  The surface is then cured for 7 days.  It is then scrubbed and cleaned thoroughly and cement grout is applied again.  After 6 days curing, final grinding is done with carborundom stone of 320-grid size.  Then it is washed with dilute oxalic solution and finally  the floor is polished with the machine Roofs • Roof is defined as the upper most part of a building , which is constructed in the form of a frame work to give protection to the buildings against rain, heat, snow, wind etc… • Roofs protect buildings and occupants from wind, rain, cold, sun, heat, dust, etc. • Roofs come in many shapes Charecterstics of roof: • The characteristics of a roof are dependent upon the purpose of the building that it covers, • the available roofing materials and the local traditions of construction and wider concepts of architectural design. • In most countries a roof protects primarily against rain. • A verandah may be roofed with material that protects against sunlight but admits the other elements. Requirements or qualities of an ideal roof: • A roof must be weather resistant to rain, snow, wind and sun. • The durability of a roof should be equal to or in excess of those materials used in the remainder of the building. • A roof should have good thermal insulation properties. • A roof should require a minimum of maintenance.
  26. 26. • A roof should be constructed in such a way as to retain structural stability when dead and imposed loads are applied to it ( dead loads is the weight of materials used to make the roof, imposed loads are loads created by wind, snow, etc. Elements of a roof: When designing a roof the following points should be considered in relation to its final appearance.  Span:- clear distance between the supports.  Rise:- vertical distance between ridge and wall plate.  Pitch:- ratio of rise to span.
  27. 27.  Ridge:- apex or headline of a slopping roof  Hip:- external angle formed at the intersection of two roof slopes.  Eaves :- lower edge of a sloping roof  Gable:-If roof slopes in two direction, the closing wall in that portion may be a combination of triangular and rectangular wall.The triangular upper part of the wall formed at the end of pitched roof is known as Gable.  Valley:-When two roof surfaces together at an angle less than 180 degree,a valley is formed.  Purlins:- wooden members are connected to trusses and to support common rafters It placed horizontally over the principal rafter  Rafters:- Inclined member placed above the purlins and extend from ridge to eave. Common rafters are intermediate rafters, which give support to the roof covering (30- 45cm spacing)  Batten :-Small c/s of wood, fixed on common rafter to support roofing material.  Cleat:-Small pieces of steel or timber, angel or channel section, used to connect purlins to principal rafter. Flat roofs  A roof is designated as flat if its slope is less than ten degrees.  Flat roofs have traditionally been used in hot climates where water accumulation is not a problem.  Slope less than 3:12 or 25 percent  If the slope is too shallow, puddles of water will stand for extended periods  Leading to premature deterioration of the roofing materials in those areas  If water accumulates cause by structural deflection, progressive structural collapse becomes possibility
  28. 28. Advantages of flat roof design:  No space lost below roof, i.e. no dead space  Less material is used than in a sloped roof  The rooftop is potentially useful as a terrace, or sleeping porch  Potentially pleasing appearance  Easier to build than a sloped roof Disadvantages of flat roof • Roof elements can not overlap, hence waterproofing must be more complex, and more thorough • Drainage is not automatic • Support of snow load must be insured Types of flat roofs  Madras terrace roof  Reinforced brick cement roof  Reinforced cement concrete roof Madras terrace roof  Wooden flat roof  Roof having slope less than 1 in 100  Teak wood joist are placed on rolled steel joists.  Sufficient slope is provided o Terrace bricks of size 15x75x25mm to be laid diagonally. o Brick bat concrete of thickness 75mm to be laid  Rammed and allow to set for three days.  Flat tiles are then laid over this concrete.  Surface of this roof is finished with 3 coats of plaster.
  29. 29. Reinforced brick cement roof  Bricks are laid horizontally between the steel bars and concrete mix is inserted in the joints.  Top surface of the slab is plastered with a 2cm thick cement mortar.  Over that apply two layers of hot bitumen for water proofing.  Over that bitumen coat apply one more coat of cement paste of thickness 5cm.  Provide sufficient slope at top surface for drainage of water Reinforced cement concrete roof  Made up of concrete and steel. Types of roof slab:-  One way slab:- length/width > 2  Two way slab:- length/width < 2 For one way slab  Reinforcement to be run parallel to the shorter span For two way slab  Main reinforcement runs parallel to both sides of the room  At corners suitable mesh reinforcement to be provided to resist temperature stresses
  30. 30. Pitched roofs Sloping top surface they are suitable for places where rainfall or snowfall is heavy. Types of pitched roofs o Lean-to-roof o Couple roof o Couple close roof o Collar and tie roof – double or purlin roof Lean-to-roof  It is used covering verandah, sheds and outhouses connected to main building.  Upper side common rafters are supported on a wall plate which in turn rest on a projecting corbel stone from the wall.  Lower side rest on the wall plate.  Roofing material rests on battens, battens on common rafter and common rafter on wall plate.  Maximum span of the roof is 2.5m
  31. 31. Couple roof  It is formed by a pair of inclined rafters, centre ridge piece and wall plate for supporting the whole roof.  Battens are supported on common rafters and roofing material on battens  Span of couple roof is limited to 3.5m Couple close roof  Similar to couple.  Two rafters are connected by a wooden member which acts as a tie.  Tie prevents the outward spreading of roof  It can also act as support for ceiling.  It can be economically used for spans up to 4.2m.
  32. 32. Collar beam roof  Members are same but just raising the position of tie beam.  Used to increase the height of room  For spans between 4 to 4.5m
  33. 33. Collar and tie roof/purlin roof or double roof  For spans greater than 3m rafters are uneconomical  To reduce the size of rafters, intermediate supports called purlins  Roof can be economically adopted for spans up to 4.8m  It is also Also known as purlin roof or double roof  Trussed roofs • A truss consists of typically straight members connected at joints, traditionally termed panel points. King post truss  Used when span > 5m  The triangular shape of truss frame offers greater rigidity.  Central vertical post-king post-provides support for tie beam.  Two inclined members provided on either side of king post- strut-used to prevent the principal rafter from bending at the Centre.  It is used for spans up to 5m to 8m
  34. 34. Queen post truss  Two vertical post- queen post – 8m to 13m span  Straining beam is provided to keep upper end of queen post in position and to counteract the thrust of struts.  Straining sill is provided on the tie beam.

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complete notes of unit 4 in bmc according jntuk r13 2-1 syllabus


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