REINFORCED CEMENT CONCRETE Lab Manual



Roll No:____Name:__________________Year:____ Semester:___REINFORCED CEMENT CONCRETE Lab Manual-937895170180CERTIFICATECertified that this file is submitted byShri/Ku.___________________________________________________________Roll No.________a student of ________ year of the course ________________________________________________________ as a part of PRACTICAL/ORAL as prescribed by the Rashtrasant Tukadoji Maharaj Nagpur University for the subject_____________________________________ in the laboratory of ___________________________________during the academic year _________________________ and that I have instructed him/her for the said work, from time to time and I found him/her to be satisfactory progressive.And that I have accessed the said work and I am satisfied that the same is up to that standard envisaged for the course.Date:- Signature & NameSignature & Name of Subject Teacher of HODAnjuman College of Engineering and TechnologyVisionTo be a centre of excellence for developing quality technocrats with moral and social ethics, to face the global challenges for the sustainable development of society.MissionTo create conducive academic culture for learning and identifying career goals.To provide quality technical education, research opportunities and imbibe entrepreneurship skills contributing to the socio-economic growth of the Nation.To inculcate values and skills, that will empower our students towards development through technology.Vision and Mission of the DepartmentVision:To be the centre of excellence for developing quality Civil Engineers with moral and social ethics to face global challenges for the sustainable development of society.Mission:To create conductive academic culture for learning and identifying career goals. To impart quality technical education along with research opportunities.To impart knowledge and generate entrepreneurship skills contributing to socio-economic growth of the nation.To inculcate values and skills, that will empower our students, towards National development through technology, to preserve nature and its resources.Program Educational Objectives (PEOs)Apply technical knowledge to find solution to the challenges in various areas and to develop independent thinking in the field of Civil Engineering.Have analyze, design, technical and soft skills, for solving problem Civil Engineering.Inculcate morality professionals and ethical sense and self confidence.Take higher education or lifelong learning and contribute in research and development throughout life.Program Specific Outcomes (PSOs)An ability to plan, analyze, design and execute low cost housing and construction works.An ability to provide the basic facilities with optimal utilization of resources to meet the societal needs.PROGRAM: CE DEGREE: B.ECOURSE: Reinforced Cement ConcreteSEMESTER: V CREDITS: COURSE CODE: BECVE502PCOURSE TYPE: REGULARCOURSE AREA/DOMAIN: CONTACT HOURS: 2 hours/Week.CORRESPONDING LAB COURSE CODE : LAB COURSE NAME : Reinforced Cement ConcreteCOURSE PRE-REQUISITES:C.CODECOURSE NAMEDESCRIPTIONSEMBECVE402PReinforced Cement ConcreteVLAB COURSE OBJECTIVES: Student shall able to Design of beams, columns, slab and foundation as per relevant IS CodeUnderstanding the professional RCC drawing.Visit at least one site visit pertaining to above designCOURSE OUTCOMES: Design PatternsAfter completion of this course the students will be able -SNODESCRIPTIONBLOOM’S TAXONOMY LEVELCO.1Apply the knowledge in actual structural design for various buildings.3CO.2Make use of structural design knowledge in reading and understanding the professional RCC drawing and draw an appropriate conclusion.6CO.3Explain the implementation of working drawing and write a report during the visit to any construction site.5CO.4Apply the concepts of design to find the various solution 3CO.5Use the knowledge of structural design to deal with complex problems3Lab Instructions:Students should come to the lab/class on time unless prior permission is obtained from thesupervisor. As per department policy, a grace period of 10 minutes will be given to latestudents. Student arriving after 10 minutes of the starting time will be considered absent.Hence, he/she will automatically receive “zero” mark for the lab report.Students will be divided into groups (preferably 5/6 students in a group). Each groupwill be given a handout. This will serve as a guide for them throughout the practical.All students must have to submit the practical report just after the entrance and before the class start.Practical reports have to be submitted serially.Students have to complete the sample calculations in class and take sign fromthe course teacher. (In some practical which require more times, should be completedas possible in class time.)Continuous Assessment PracticalExp NoNAME OF EXPERIMENTDateSignRemark1Design of Beams2Design of Slabs3Design of Columns4Design of Footing5Site VisitCONTENTSExp NoNAME OF EXPERIMENTDateSignRemark1Design of Beams2Design of Slabs3Design of Columns4Design of Footing5Site VisitPRACTICAL NO – 1 DESIGN OF BEAMSDesign of BeamsIn this practical, it is intended to learn the method of designing the beams using the principles developed in previous chapters. Design consists of selecting proper materials, shape and size of the structural member keeping in view the economy, stability and aesthetics. The design of beams are done for the limit state of collapse and checked for the other limit states. Normally the beam is designed for flexure and checked for shear, deflection, cracking and bond.Design procedureThe procedure for the design of beam may be summarized as follows:1. Estimation of loads2. Analysis3. Design1. Estimation of loadsThe loads that get realized on the beams consist of the following:a. Self-weight of the beam.b. Weight of the wall constructed on the beamc. The portion of the slab loads which gets transferred to the beams. These slab loads are due to live loads that are acting on the slab dead loads such as self-weight of the slab, floor finishes, partitions, false ceiling and some special fixed loads.The economy and safety of the beams achieved depends on the accuracy with which the loads are estimated. The dead loads are calculated based on the density whereas the live loads are taken from IS: 875 depending on the functional use of the building.2. AnalysisFor the loads that are acting on the beams, the analysis is done by any standard method to obtain the shear forces and bending moments.3. Designa. Selection of width and depth of the beam.The width of the beam selected shall satisfy the slenderness limits specified in IS 456: 2000 clause 23.3 to ensure the lateral stability.b. Calculation of effective span (le) (Refer clause 22.2, IS 456:2000)c. Calculation of loads (w)d. Calculation of critical moments and shears.The moment and shear that exists at the critical sections are considered for the design. Critical sections are the sections where the values are maximum. Critical section for the moment in a simply supported beam is at the point where the shear force is zero. For continuous beams the critical section for the +ve bending moment is in the span and –ve bending moment is at the support. The critical section for the shear is at the support.e. Find the factored shear (Vu) and factored moment (Mu)f. Check for the depth based on maximum bending moment.Considering the section to be nearly balanced section and using the equation Annexure G, IS 456-2000 obtaining the value of the required depth d required. If the assumed depth “d” is greater than the “d required”, it satisfies the depth criteria based on flexure. If the assumed section is less than the” d required”, revise the section.g. Calculation of steel.As the section is under reinforced, use the equation G.1.1.(b) to obtain the steel.h. Check for shear.i. Check for developmental length.j. Check for deflection.k. Check for Ast min, Ast max and distance between the two bars.Anchorage of bars or check for development lengthIn accordance with clause 26.2 IS 456: 2000, the bars shall be extended (or anchored) for a certain distance on either side of the point of maximum bending moment where there is maximum stress (Tension or Compression). This distance is known as the development length and is required in order to prevent the bar from pulling out under tension or pushing in under compression. The development length (Ld) is given bywhere, ? = Nominal diameter of the bar = Stress in bar at the section considered at design load Zbd= Design bond stress given in table 26.2.1.1 (IS 456: 2000)Table 26.2.1.1: 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 M 40 and aboveDesign bond stress 1.2 1.4 1.5 1.7 1.9IMPORTANT NOTESDue to the above requirement it can be concluded that no bar can be bent up or curtailed up to a distance of development length from the point of maximum moment.Due to practical difficulties if it is not possible to provide the required embedment or development length, bends hooks and mechanical anchorages are used.Flexural reinforcement shall not be terminated in a tension zone unless any one of thefollowing condition is satisfied:The shear at the cut-off points does not exceed two-thirds that permitted, including the shear strength of web reinforcement provided.Stirrup area in excess of that required for shear and torsion is provided along each terminated bar over a distance from the cut-off point equal to three-fourths the effective depth of the member. The excess stirrup area shall be not less than 0.4bs/fy, where b is the breadth of the beam, s is the spacing and fy is the characteristic strength of reinforcement in N/mm2. The resulting spacing shall not exceed d/8_ where _ is the ratio of the area of bars cut-off to the total area of bars at the section, and d is the effective depth.For 36 mm and smaller bars, the continuing bars provide double the area required for flexure at the cut-off point and the shear does not exceed three-fourths that permitted.Positive moment reinforcementAt least one-third the positive moment reinforcement in simple members and one fourth the positive moment reinforcement in continuous members shall extend along the same face of the member into the support, to a length equal to Ld/3.When a flexural member is part of the primary lateral load resisting system, the positive reinforcement required to be extended into the support as described in (a) shall be anchored to develop its design stress in tension at the face of the support.At simple supports and at points of inflection, positive moment tension reinforcement shall be limited to a diameter such that Ld computed for fd by 26.2.1 IS 456:2000 does not exceed.Where, M1 = moment of resistance of the section assuming all reinforcement at the section to be stressed to fdfd = 0.87fy in the case of limit state design and the permissible stress in the case of working stress design;V = shear force at the section due to the design loads;L0 = sum of the anchorage beyond the centre of the support and the equivalent anchorage value of any hook or mechanical anchorage at simple support; and at a point of inflection, L0 is limited to the effective depth of the members or 12? , whichever is greater; and? = Diameter of barThe value of M1/V in the above expression may be increased by 30 percent when the ends of the reinforcement are confined by a compressive reaction.Negative moment reinforcementAt least one third of the total reinforcement provided for negative moment at the support shall extend beyond the point of inflection for a distance not less than the effective depth of the member of 12? or one-sixteenth of the clear span whichever is greater.Anchorage of barsAnchoring of bars is done to provide the development length and maintain the integrity of the structure.Anchoring bars in tensionDeformed bars may be used without end anchorages provided development length requirement is satisfied. Hooks should normally be provided for plain bars in tension.Bends and hooks – shall conform to IS 2502Bends – The anchorage value of bend shall be taken as 4 times the diameter of the bar for each 450 bend subject to a maximum of 16 times the diameter of the bar.Hooks – The anchorage value of a standard U-type hook shall be equal to 16 timesthe diameter of the bar.Anchoring bars in compressionThe anchorage length of straight bar in compression shall be equal to the development length of bars in compression as specified in clause 26.2.1 of IS 456:2000. The projected length of hooks, bends and straight lengths beyond bends if provided for a bar in compression, shall only be considered for development length.Anchoring shear reinforcementa. Inclined bars – The development length shall be as for bars in tension; this length shall be measured as under:1. In tension zone, from the end of the sloping or inclined portion of the bar, and2. In the compression zone, from the mid depth of the beam.b. Stirrups – Not withstanding any of the provisions of this standard, in case of secondary reinforcement, such as stirrups and transverse ties, complete development lengths and anchorages shall be deemed to have been provided when the bar is bent through an angle of at least 900 round a bar of at least its own diameter and is continued beyond the end of the curve for a length of at least eight diameters, or whenthe bar is bent through an angle of 1350 and is continued beyond the end of the curve for a length of at least six bar diameters or when the bar is bent through an angle of 1800 and is continued beyond the end of the curve for a length of at least four bar diameters.Reinforcement requirements1. Minimum reinforcementThe minimum area of tension reinforcement shall be not less than that given by the followingWhere, As = minimum area of tension reinforcement.b = breadth of beam or the breadth of the web of T-beam,d = effective depth, andfy = characteristic strength of reinforcement in N/mm22. Maximum reinforcementThe maximum area of tension reinforcement shall not exceed 0.04bDCompression reinforcementThe maximum area of compression reinforcement shall not exceed 0.04bD. Compression reinforcement in beams shall be enclosed by stirrups for effective lateral restraint.Slenderness limits of beams to ensure lateral stabilityA beam is usually a vertical load carrying member. However, if the length of the beam is very large it may bend laterally. To ensure lateral stability of a beam the following specifications have been given in the code.A simply supported or continuous beam shall be so proportioned that the clear distance between the lateral restraints does not exceed 60b or 250 b2/d whichever is less,Where d is the effective depth of the beam b the breadth of the compression face midway between the lateral restraints.For a cantilever, the clear distance from the free end of the cantilever to the lateralrestraint shall not exceed 25b or 100 b2/d whichever is less.Reinforcement detailing For RCC detailing refer SP 34PRACTICAL NO – 2DESIGN OF SLABSA slab is a flat two dimensional planar structural element having thickness small compared to its other two dimensions. It provides a working flat surface or a covering shelter in buildings. It primarily transfer the load by bending in one or two directions. Reinforced concrete slabs are used in floors, roofs and walls of buildings and as the decks of bridges. The floor system of a structure can take many forms such as in situ solid slab, ribbed slab or pre-cast units. Slabs may be supported on monolithic concrete beam, steel beams, walls or directly over the columns. Concrete slab behave primarily as flexural members and the design is similar to that of beams.CLASSIFICATION OF SLABS1) Based of shape: Square, rectangular, circular and polygonal in shape.2) Based on type of support: Slab supported on walls, Slab supported on beams, Slab supported on columns (Flat slabs).3) Based on support or boundary condition: Simply supported, Cantilever slab, Overhanging slab, Fixed or Continues slab.4) Based on use: Roof slab, Floor slab, Foundation slab, Water tank slab.5) Basis of cross section or sectional configuration: Ribbed slab /Grid slab, Solid slab, Filler slab, folded plate6) Basis of spanning directions:One way slab – Spanning in one directionTwo way slab _ Spanning in two directionDESIGN GUIDELINES FOR ONEWAY SLAB1 Load on slab:The load on slab comprises of Dead load, floor finish and live load. The loads are calculated per unit area (load/m2).Dead load = D x 25 kN/m2 ( Where D is thickness of slab in m)Floor finish (Assumed as)= 1 to 2 kN/m2Live load (Assumed as) = 3 to 5 kN/m2 (depending on the occupancy of the building)2 Effective span of slabEffective span of slab shall be lesser of the twol = clear span + d (effective depth )l = Center to center distance between the support3 Calculation of maximum Banding moment and Maximum Shear forceMax B.M = W x leff2 / 8 Treated slab as design as simply supportedMax S.F = W x leff / 2 4 Depth of slabThe depth of slab depends on bending moment and deflection criterion. the trail depth can be obtained usingEffective depth d= Span / (l/d) Basic x modification factor)For obtaining modification factor, the percentage of steel for slab can be assumed from 0.2 to 0.5%The effective depth d of two way slabs can also be assumed using cl.24.1,IS 456 provided short span is 3.5m and loading class is < 3.5KN/m25 Checks for Bending and depth of slabUsing deflection criteriaEquate Mu = Mu limitMu = 0.146 x fck x b x d2 For Fe 250 Grade of steelMu = 0.138 x fck x b x d2 For Fe 415 Grade of steelMu = 0.133 x fck x b x d2 For Fe 500 Grade of steel6 Calculation of Area of steel Ast = 0.5 fck ( ( 1 – (1- Mu / fck b d2 )1/2) b d fy7 Check for shear as per IS 456-20008 Check for deflection as per IS 456-20009 Check for Development length as per IS 456-200010 Check for cracks as per IS 456-200011 DETAILING REQUIREMENTS AS PER IS 456 -2000a. Nominal Cover For Mild exposure – 20 mmFor Moderate exposure – 30 mmHowever, if the diameter of bar do not exceed 12 mm, or cover may be reduced by 5 mm.Thus for main reinforcement up to 12 mm diameter bar and for mild exposure, the nominalcover is 15 mmb. Minimum reinforcement The reinforcement in either direction in slab shall not be less than0.15% of the total cross sectional area for Fe-250 steel0.12% of the total cross sectional area for Fe-415 & Fe-500 steel.c. Spacing of bars The maximum spacing of bars shall not exceedMain Steel – 3d or 300 mm whichever is smallerDistribution steel –5d or 450 mm whichever is smaller Where, ‘d’ is the effective depth of slab.Note: The minimum clear spacing of bars is not kept less than 75 mm (Preferably 100 mm) though code do not recommend any value.d. Maximum diameter of bar: The maximum diameter of bar in slab, shall not exceed D/8, where D is the total thickness of slab.DESIGN GUIDELINES FOR TWO WAY SLABTypes of Two Way SlabTwo way slabs are classified into two types based on the support conditions:a) Simply supported slabb) Restrained slabsTwo way simply supported slabsThe bending moments Mx and My for a rectangular slabs simply supported on all four edges with corners free to lift or the slabs do not having adequate provisions to prevent lifting of corners are obtained usingWhere, αx and αY are coefficients given in Table 1 (Table 27, IS 456-2000)W- Total load /unit arealx & ly – lengths of shorter and longer span.Table 1 Bending Moment Coefficients for Slabs Spanning in Two Directions atRight Angles, Simply Supported on Four Sides (Table 27:IS 456-2000)Note: 50% of the tension steel provided at mid span can be curtailed at 0.1lx or 0.1ly from support.Two way restrained slabsWhen the two way slabs are supported on beam or when the corners of the slabs are prevented from lifting the bending moment coefficients are obtained from Table 2 (Table 26, IS456-2000) depending on the type of panel shown in Fig.These coefficients are obtained using yield line theory. Since, the slabs are restrained; negative moment arises near the supports. The bending moments are obtained usingDetailing requirements as per IS 456-2000Slabs are considered as divided in each direction into middle and end strips as shown belowThe maximum moments obtained using equations are apply only to middle strip.50% of the tension reinforcement provided at midspan in the middle strip shall extend in the lower part of the slab to within 0.25l of a continuous edge or 0.15l of a discontinuous edge and the remaining 50% shall extend into support.50% of tension reinforcement at top of a continuous edge shall be extended for a distance of 0.15l on each side from the support and at least 50% shall be provided for a distance of 0.3l on each face from the support.At discontinuous edge, negative moment may arise, in general 50% of mid span steel shall be extended into the span for a distance of 0.1l at top.Minimum steel can be provided in the edge stripTension steel shall be provided at corner in the form of grid (in two directions) at top and bottom of slab where the slab is discontinuous at both the edges . This area of steel in each layer in each direction shall be equal to ? the area required (Ast) for maximum mid span moment. This steel shall extend from the edges for a distance of lx/5. The area of steel shall be reduced to half (3/8 Astx) at corners containing edges over only one edge is continuous and other is discontinuous. Fig.DESIGN GUIDELINES FOR ONEWAY CONTINEOUS SLABThe slabs spanning in one direction and continuous over supports are called one way continuous slabs. These are idealized as continuous beam of unit width. For slabs of uniform section which support substantially UDL over three or more spans which do not differ by more than 15% of the longest, the B.M and S.F are obtained using the coefficients available in Table 12 and Table 13 of IS 456-2000. For moments at supports where two unequal spans meet or in case where the slabs are not equally loaded, the average of the two values for the negative moments at supports may be taken. Alternatively, the moments may be obtained by moment distribution or any other methods.Bending moment and Shear force coefficients for continuous slabs( Table 12, Table 13, IS 456-2000)In case of one-way continuous slab all steps are common as that of one-way slab only bending moment and shear force calculation are based on above coefficient and the reinforcement detailing are done as per SP 34PRACTICAL NO – 3DESIGN OF COLUMNSDesign of Columns LIMIT STATE OF COLLAPSE: COMPRESSIONLongitudinal or main reinforcement IS: 456 stipulate that the main reinforcement shall satisfy the followingThe longitudinal reinforcement in a column shall be between 0.8 to 6.0 per cent of the gross cross-sectional area. However, in practice, the maximum amount of steel is restricted to 4 per cent of the gross cross-sectional area provided. In any column that has a larger cross-sectional area than that required supporting the load, the minimum percentage of steel shall be based upon the area of concrete required to resist the direct stress and not upon the actual area.In a square or rectangular column minimum of 4 bars to be provided as a longitudinal compression reinforcement.In circular or spirally reinforced columns minimum of six bars to be provided.For column of five or more side, one bar at each side to be providedSize of each bars should not be less than 12 mm diametersSpacing of longitudinal bars along the periptery should not exceed 300 mm to ensure the proper confinement of concrete.Transverse reinforcementThe diameter of the polygonal links (with internal angles < 135°) or lateral ties should not be less than one-fourth of the diameter of the largest Longitudinal] bar and in no case less than 6 mm. The diameter of the tie bar should not be more than 20 min.The pitch or spacing of lateral ties is Limited to the least of:(I) the least lateral dimension of the compression member,(ii) sixteen times the smallest diameter of longitudinal reinforcement to be tied, and(iii) 300 mmHelical reinforcementThe diameter of the helix bar shall be based on the criterion used for the ties The pitch of the spiral in the spirally reinforced column shall neither be more than the smaller of the distances: (1) 75 mm and (ii) one-sixth of the core diameter of the column nor be less than the larger of the: (a) 25 mm and (b) three times the diameter of the steel bar forming the helix. To assure that the spiral effect exceeds the shell capacity.CoverThe IS: 456 code requirements are1 For a longitudinal reinforcing bar in a column the nominal or clear cover should be more than the larger of the followinga 40 mmb Diameter of the longitudinal bar2 For a column of minimum dimension less than 200 mm. where the diameter of the reinforcing bar does not exceed 12 mm. a cover of 25 mm may be provided.3 For the hoops and ties the nominal or clear cover shall not be less than the diameter of the bar used in making the hoops or ties, nor less than 20 mm for mild exposure.PART 1Slender ColumnsPART 2Axially Loaded Short Column (with e = 0 to emin)A compression member shall be considered as a short column when slenderness ratios (l/D) and (4/ b) are less than or equal to 12. Where l and l. are effective lengths in respect of major and minor axes, respectively; D is the depth in respect of the major axis and b is the width of the member. The members carrying bending moments which are quite small as compared to the direct compressive load are termed as axially loaded columns. When the code specified minimum eccentricity emin = (JJ500) + (D/30) or 20 mm (greater of the two) does not exceed 0.05 times the lateral dimension of the column in the direction under consideration, the axial load-carrying capacity. Pu is given byPART 3Column Subjected to Combined Axial Load and Uniaxial BendingNote: - Reinforcement detailing of column are done as per SP 34PRACTICAL NO – 4DESIGN OF FOOTINGDESIGN OF FOOTINGDesign of Isolated Column FootingThe objective of design is to determineArea of footingThickness of footingReinforcement details of footing (satisfying moment and shear considerations)Check for bearing stresses and development lengthThis is carried out considering the loads of footing, SBC of soil, Grade of concrete and Grade of steel. The method of design is similar to the design of beams and slabs. Since footings are buried,deflection control is not important. However, crack widths should be less than 0.3 mm.The steps followed in the design of footings are generally iterative. The important steps in the designof footings are;Find the area of footing (due to service loads)Assume a suitable thickness of footingIdentify critical sections for flexure and shearFind the bending moment and shear forces at these critical sections (due to factored loads)Check the adequacy of the assumed thicknessFind the reinforcement detailsCheck for development lengthCheck for bearing stressesLimit state of collapse is adopted in the design pf isolated column footings. The various design stepsconsidered areDesign for flexureDesign for shear (one way shear and two way shear)Design for bearingDesign for development lengthThe materials used in RC footings are concrete and steel. The minimum grade of concrete to be usedfor footings is M20, which can be increased when the footings are placed in aggressive environment,or to resist higher stresses.CoverThe minimum thickness of cover to main reinforcement shall not be less than 50 mm for surfaces in contact with earth face and not less than 40 mm for external exposed face. However, where the concrete is in direct contact with the soil the cover should be 75 mm. In case of raft foundation the cover for reinforcement shall not be less than 75 mm.Minimum reinforcement and bar diameterThe minimum reinforcement according to slab and beam elements as appropriate should be followed, unless otherwise specified. The diameter of main reinforcing bars shall not be less 10 mm. The grade of steel used is either Fe 415 or Fe 500.Specifications for Design of footings as per IS 456 : 2000The important guidelines given in IS 456 : 2000 for the design of isolated footings are as follows:GeneralFootings shall be designed to sustain the applied loads, moments and forces and the induced reactions and to ensure that any settlement which may occur shall be as nearly uniform as possible, and the safe bearing capacity of the soil is not exceeded (see IS 1904).In sloped or stepped footings the effective cross-section in compression shall be limited by the area above the neutral plane, and the angle of slope or depth and location of steps shall be such that the design requirements are satisfied at every section. Sloped and stepped footings that are designed as a unit shall be constructed to assure action as a unit.Thickness at the Edge of FootingIn reinforced and plain concrete footings, the thickness at the edge shall be not less than 150 mm forfootings on soils, nor less than 300 mm above the tops of piles for footings on piles.In the case of plain concrete pedestals, the angle between the plane passing through the bottom edge of the pedestal and the corresponding junction edge of the column with pedestal and the horizontal plane (see Fig. 20) shall be governed by the expressionWhere= calculated maximum bearing pressure at the base of the pedestal in N/mm2 = characteristic strength of concrete at 28 days in N/mm2.Moments and ForcesIn the case of footings on piles, computation for moments and shears may be based on the assumption that the reaction from any pile is concentrated at the centre of the pile.For the purpose of computing stresses in footings which support a round or octagonal concrete column or pedestal, the face of the column or pedestal shall be taken as the side of a square inscribed within the perimeter of the round or octagonal column or pedestal.Bending MomentThe bending moment at any section shall be determined by passing through the section a vertical plane which extends completely across the footing, and computing the moment of the forces acting over the entire area of the footing on one side of the said plane.The greatest bending moment to be used in the design of an isolated concrete footingwhich supports a column, pedestal or wall, shall be the moment computed in the manner at sections located as followsAt the face of the column, pedestal or wall, for footings supporting a concrete column, pedestal or wallHalfway between the centre-line and the edge of the wall, for footings under masonry walls; andHalfway between the face of the column or pedestal and the edge of the gusseted base, for footings under gusseted bases.Tensile ReinforcementThe total tensile reinforcement at any section shall provide a moment of resistance at least equal to the bending moment on the section Total tensile reinforcement shall be distributed across the corresponding resisting section as given below:In one-way reinforced footing, the-reinforcement extending in each direction shall be distributed uniformly across the full width of the footing;In two-way reinforced square footing, the reinforcement extending in each direction shall be distributed uniformly across the full width of the footingIn two-way reinforced rectangular footing, the reinforcement in the long direction shall be distributed uniformly across the full width of the footing. For reinforcement in the short direction, a central band equal to the width of the footing shall be marked along the length of the footing and portion of the reinforcement determined in accordance with the equation given below shall be uniformly distributed across the central band:where β is the ratio of the long side to the short side of the footing. The remainder of the reinforcement shall be uniformly distributed in the outer portions of the footing.Transfer of Load at the Base of ColumnThe compressive stress in concrete at the base of a column or pedestal shell is considered as being transferred by bearing to the top of the supporting Pedestal or footing. The bearing pressure on the loaded area shall not exceed the permissible bearing stress in direct compression multiplied by a value equal tobut not greater than 2, where A1 = supporting area for bearing of footing, which in sloped or stepped footing may be taken as the area of the lower base of the largest frustum of a pyramid or cone contained wholly within the footing and having for its upper base, the area actually loaded and having side slope of one vertical to two horizontal; and A2 = loaded area at the column base.Where the permissible bearing stress on the concrete in the supporting or supported member would be exceeded, reinforcement shall be provided for developing the excess force, either by extending the longitudinal bars into the supporting member, or by dowels (see 34.4.3).Where transfer of force is accomplished by, reinforcement, the development length of the reinforcement shall be sufficient to transfer the compression or tension to the supporting memberExtended longitudinal reinforcement or dowels of at least 0.5 percent of the cross-sectional area of the supported column or pedestal and a minimum of four bars shall be provided. Where dowels are used, their diameter shall no exceed the diameter of the column bars by more than 3 mm.Column bars of diameters larger than 36 mm, in compression only can be dowelled at the footings with bars of smaller size of the necessary area. The dowel shall extend into the column, a distance equal to the development length of the column bar and into the footing, a distance equal to the development length of the dowel.Nominal ReinforcementMinimum reinforcement and spacing shall be as per the requirements of solid slab.The nominal reinforcement for concrete sections of thickness greater than 1 m shall be 360 mm2 per metre length in each direction on each face. This provision does not supersede the requirement of minimum tensile reinforcement based on the depth of the section.Note :- RCC detailing are done as per SP 34 ................
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