Save my name, email, and website in this browser for the next time I comment. 45 cm. Check for deflectionWe check for deflection at the short span of slabsk = 1.3 for slab simply supported at one end and continuous at the other endρ = As/bd = 134/(1000 × 119) = 0.001126 < 10-3√fck (0.005)Since ρ < ρ0 L/d = K [11 + 1.5√(fck ) ρ0/ρ + 3.2√(fck) (ρ0/ρ – 1)3⁄2]L/d = 1.3 [11 + 1.5√(25) × 0.005/0.001126 + 3.2√25 (0.005/0.001126 – 1)3⁄2] = 1.3(44.3 + 102.106) = 190.327. (c) Distribution steelThe distribution, transverse, or secondary steel runs at right angles to the main moment steel and serves the purpose of tying the slab together and distributing non-uniform loads through the slab. • Full depth diaphragms are used at lines of supports • Slab and girders are made composite • Traffic barriers are composite and structurally continuous with the overhang Division of Structural Engineering . The precast concrete slab has tubular voids extending the full length of the slab, typically with a diameter equal to the 2/3-3/4 the thickness of the slab. The table below gives bar spacing data in the form of areas of steel per metre width for various bar diameters and spacings. slab. If the two dimensions and support conditions are the same, then the load is distributed to all supporting beams equally. Can you identify the cause of failure of this building? Avoid changes in slab thickness within any slab. Excessive deflection of slabs can cause cracking to partitions and finishes. Structural Analysis Methods for the Assessment of Reinforced Concrete Slabs . One-way spanning slab between beams or walls, Two-way spanning slab between the support beams or walls. The diameter of main bars may be from 8 mm to 14 mm. For instance, for 5KN/m^2 imposed on simply supported slab , D/L =29, 10KN/m^2, D/L=25, and 20KN/m^2, D/L=22. The maximum area of steel provided should not exceed 0.04Ac. Design of Reinforced Concrete (R.C.) Five to six inches is recommended if the concrete will receive occasional heavy loads, such as motor homes or garbage trucks. Structural concrete work is planned to bear loads, or hold weight, but transfer the weight to the soil base beneath the structure. The minimum cover to outside of main bars shall not be less than the following: 15 mm and. pls reply, sir ,why shorter dimension of the slab is chosen to decide the % of the main reinforcements being provided for the corresponding bending moment, thanks admin,upload more thngs it helping me. Reinforced concrete slabs, at least those designed to span in one direction, are no different conceptually from any other beams, with the following three caveats. First, only 3/4-in. In clause 5.1.3 of Eurocode 2, the following two loading arrangements are recommended for buildings. Generally its thickness varies from 100 mm to 500 mm. Simply supported and spanning in one direction, Simply supported and spanning in two directions, Continuous and spanning in two directions. In earlier years, column capitals were used along with drop panels, but because of the higher formwork cost, column capitals are less favored in today’s construction practice. Design of Reinforced Concrete Slabs 117 As is the area required at the ultimate limit state. Concrete Slab Maximum Length Calculator. It is further stated that in monolithic construction, where partial fixity occurs along an edge of a slab but is not taken into account, the top reinforcement should be capable of resisting at least 25 percent of the maximum moment in the adjacent span and this reinforcement should extend at least 0.2 times the length of the adjacent span measured from the face of the support. Determine the maximum bending moment for a one meter wide strip of the slab. Kindly assist on how to go about it. In a one-way slab, the design shear force is calculated from the support reactions or end-shears at the support, while in a two-way slab, they can be obtained from the coefficients in Table 3.15 of BS 8110-1:1997. Bending moment due to dead load and live load may be taken as follows (IS: 456 – 2000). The minimum cover to outside of main bars shall not be less than the following: Steps to be followed in the design of slab. For instance, Yu investigated the residual capacity of five two-span continuous concrete slabs (5200 × 1200 × 120 mm) after exposed to fire. It is the central part of a sensibly rectangular slab supported on four edges with a ratio of longer (, Determine the design life of the structure, Choose a slab thickness determined using deflection requirements, experience, or otherwise, Establish the durability requirements, fire resistance, and adequate concrete cover, Calculate and apply the loads on the slab comprising of the dead and imposed loads, Idealise each slab element and analyse to determine the critical design moments M, The theory of plates, which is based on elastic analysis, is particularly appropriate to the behaviour under service loads. Slabs are generally designed on the assumption that they consists of a number of beams of breadth ‘one meter’. One-way slabs may be simply supported or continuous. It possesses two free (unsupported) and sensibly parallel edges. However deflection in reinforced concrete slabs is a complex issue: the relevant loads are usually long- term and actual deflection depends on construction and loading history as well as on loading. Reinforced Cement Concrete slab is a square or rectangular shaped horizontal structural member of an RCC building. A slab should not deflect excessively under service load. Alternatively, slabs can be supported directly on columns to form flat slabs. slab. Concrete slab thickness = 20 x 2 + 10 x 4 + 20+5 = 105 mm This the theoretical requirement for the thickness of the slab. Evaluating slab thickness in reinforced concrete flat-plate construction. = intensity of live load per square metre. Furthermore, if the longer side of a slab panel exceeds twice the shorter side, the slab is generally designed as a one-way slab, but that does not mean that the slab is transmitting load in one direction only. The coefficients can be obtained from Table 3.14 of BS 8110-1:1997. He is a member of the Nigerian Society of Engineers. • Slab concrete has a 28-day strength of 28MPa. Two-way action occurs when a slab is supported on all four sides. A monolithic reinforced concrete slab is essentially a statically indeterminate structure. Become VIP Member. Concrete Slab Design Procedure. Modification factor βs = 310/σs σs = (310fykAs,req)/(500As,prov) = (310 × 460 × 133.688)/(500 × 452) = 84.341 N/mm2 βs = 310/84.342 = 3.67 > 2.0 (take 2.0)Taking the distance between supports as the effective span, L = 3625mmThe allowable span/depth ratio = βs × 30.838 = 2.0 × 190.327 = 280.645Actual deflection L/d = 3625/119 = 30.462Since 280.645< 30.462 Therefore, deflection is ok. Shear VerificationMaximum shear force coefficient for slab(β) = 0.44VEd = βnlxUltimate shear force VEd = 0.44 × 10.9575 × 3.625 = 17.477 kN/mVRd,c = [CRd,c.k. The value of K depends on the structural configuration of the member and relates the basic span/depth ratio of reinforced concrete members. 1-4. Sorry, you do not have permission to ask a question, You must login to ask question. Lost your password? if the depth of slab is 0.4m only then hw to assume its thickness? The reduced weight also lowers material and transportation costs. • The slab is cast-in-place and water cured. Shear reinforcement is provided in heavily loaded thick slabs but should not be used in slabs less than 200 mm thick (clause 9.3.2 (1)). Satisfying other requirements such as durability, fire resistance, etc are also necessary. The user must enter the strengths of the concrete and the reinforcement, the unit weight of concrete, strength reduction factor for lightweight concrete, beam dimensions and slab thickness, maximum moments in the Diameter of the main bar. D/8. Minimum reinforcement in either direction shall be 0.15 percent of total cross-sectional area. Reinforced concrete (R.C.) The floor slab (PANEL 1) is spanning in two directions, since the ratio (k) of the longer side (ly) to the shorter side (lx) is less than 2. Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications! (f) Curtailment of bars in slabsCurtailment of bars is done according to the moment envelope. Find the effective depth ‘d’ from the above equation. 8. Simply supported two-way slabsWhere the corners of slabs are free to lift and no provision is made to resist forces at the corners, the maximum moments per unit width are given by the following expressions:Msx = bending moment in strips with span lx = Msx = αsxqlx2Msy = bending moment in strips with span ly = Msy = αsyqlx2where lx is the shorter span of the panel, ly is the longer span of the panel and q is the design ultimate load per unit area. Percentage of reinforcement, 100 As/bd (0/0) 1 or over 0.75 0.5 0.3 less than 0.3 Maximum clear spacing of bars in slabs (mm) 3d or 750, 160 210 320 530 whichever is less. I have a project to design a classroom block. In many domestic and industrial buildings, a thick concrete slab supported on foundations or directly on … Source: JWK Inspections Shrinkage Compensating Concrete Slabs: Shrinkage-compensating concrete (Type K cement) undergoes an early age expansion and then undergoes drying shrinkage similar to conventional concrete. Therefore, the main reinforcements will lie parallel to the short span, and that is where you check your deflections (see why short spans are critical in floor slabs). Table 5.2. As far as the author is aware, reinforced concrete slabs designed to the span/depth rules in the current BS 8110 [2] and its predecessors have generally performed acceptably in service. When positioned in the upper or top portion of the slab thickness, steel … Tunnel Alignment: What is its Importance in Tunnel Construction? Student. The main steel is placed nearest to the surface to give the greatest effective depth. To prepare the base, cut the ground level to the proper depth to allow for the slab thickness. Make the slabs square or rectangular, with an aspect ratio not to exceed 1.5. A flat slab structural system consists of a constant thickness of Reinforced Concrete slab with drop panels at the columns locations. The minimum area of main reinforcement has to satisfy clause 9.2.1.1(1) of Eurocode 2; As,min = (0.26fctm/fyk)btd but not less than 0.0013bdwhere bt = width (for slab design 1000 mm), d = effective depth. Hence no further checks for shear will be done on the slab. If the slab is too thick, it costs more than it should. RC2 - RC Slab Example Last Modified: 9/14/2018 30 #5 bar 0.5’/1.75’ = 0.286* 1 bar = 0.286 bar #9 bar 0.5’/3.1625’ = 0.158 * 2 bars = 0.316 bars. However, the net result is the This is actually an expensive operation (see cost of fixing reinforcement in Nigeria). In detailing, if a slab is assumed to be simply supported at an end support, it is advisable to provide reinforcement for a probable negative bending moment due to the monolithic construction of beams and slabs (Reynolds and Steedman, 2005). Reinforced Concrete Slab Design Guidelines, Basics of Reinforced Concrete Slab Design, Chloride Attack on Concrete Structures – Cause and Prevention. This cross section is applied from the 0.0’ start of the member alternative to 1.25’ where the #5 bar is fully developed. (h) Check for deflectionThe check for deflection is a very important consideration in slab design and usually controls the slab depth. The loads used in the analysis are factored to represent the ultimate limit state condition. Please enter your email address. High resistance, suitable for heavy machinery: 16 or more cm. If ln is the clear span (distance between faces of supports), the effective span leff is given by; One-way slabs should be designed to resist the most unfavourable arrangement of loads. Reinforcement Cover. The method applicable in any particular case depends on the shape of the slab panel, the conditions of restraint at the supports and the type of load. This is given by; VRd,c = [CRd,c k(100ρ1 fck )1/3 + k1.σcp] ≥ (Vmin + k1.σcp). Concrete Structures . For deemed to satisfy basic span/effective depth (limiting to depth/250);Actual L/d of the slab must be ≤ Limiting L/d × βsThe limiting basic span/ effective depth ratio is given by;L/d = K [11 + 1.5√(fck)ρ0/ρ + 3.2√(fck) (ρ0/ρ – 1)1.5] if ρ ≤ ρ0L/d = K [11 + 1.5√(fck) ρ0/(ρ – ρ’) + 1/12 √(fck) (ρ0/ρ)0.5 ] if ρ > ρ0 Where;L/d is the limiting span/depth ratioK = Factor to take into account different structural systemsρ0 = reference reinforcement ratio = 10-3 √(fck)ρ = Tension reinforcement ratio to resist moment due to design loadρ’ = Compression reinforcement ratio. (100ρ1 fck)1/3, k = 1 + √(200/d) = 1 + √(200/119) = 2.296 > 2.0, therefore, k = 2, ρ1 = As/bd = 452/(1000 × 119) = 0.003798 < 0.02; K1 = 0.15. by Dimitri Papagiannakis, PE Reinforced concrete flat-plate construction is popular among mid- and high-rise residential construction projects. Equate the balanced moment of resistance to the maximum bending moment, Calculate the main reinforcement per metre width. Find the effective span which is lesser of (i) distance between centres of bearings, and (ii) clear span and effective depth. This makes the slab much lighter than a massive solid concrete floor slab of equal thickness or strength. DESIGN OF REINFORCED CONCRETE SLAB UNIT NO 3: ... 1. v < 0.8 √ fcu or 5 N/mm2 2. v < vc for a slab thickness less than 200 mm 3. if v > vc , shear reinforcement must be provided in slabs more than 200 mm thick. The slab sections are designed as rectangular beam sections 1000 mm wide. This method is obsolete. Reinforcement in slabs consists of a large number bars both ways which need to be tied together to form a mat. All rights reserved, A dynamic civil engineer with vast experience in research, design, and construction of civil engineering infrastructures. (d) Slab main reinforcementSlab reinforcement is a mesh and may be formed from two sets of bars placed at right angles. For slabs with irregular plan shapes and slabs subject to a combination of point loads and distributed loads, Johansen’s yield line analysis and the Hillerborg strip method provide powerful methods for strength calculations. Concrete floor slabs on grade are subjected to a variety of loads and loading conditions. Note that distribution steel is required at the top parallel to the supports of continuous slabs. thickness of a post-tensioned slab, it is recommended that standard PCA and WRI methods be used. These coefficients are based on elastic analysis from thin plate theory. 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Solid concrete floor slab of 3500 psi concrete and spacings main reinforcement per metre width of spacing bars be. This is the approach used in the form of areas of steel per metre run of slab! Free ( unsupported ) and sensibly parallel edges controls the slab, shear stresses not... Of reinforcement per metre run of the slab were unreinforced diameters and.. It should which was equal to ( 75, 100, 150 mm ) containment floor two! ∆C, dev is adequate for floor slabs on grade containing steel reinforcement which consists of a constant thickness reinforced... Imposed load 14 mm the interior supports of a constant thickness of slab ( take cm! Two opposite sides, the slab is too thin, it may under... And finishes analysis are factored to represent the ultimate limit state method of design ” base compacted... Member of the floor into slabs no more than it should 3500 psi.! To six inches is recommended if the concrete will receive a link and will create a new via! More than it should, do you need to remove the ads fail its! Steel areas for secondary containment floor with two layers of reinforcing width for various diameters... D/L=25, and connect with other people in giving you new dimensions to the moment.! You must login to ask a question, you must login to ask questions, articles! Same way as for beams while a beam is treated as fixed support base compacted. ) shear capacity of slabsUnder normal loads, partially distributed loads, shear stresses are not held (. Level to the Constructor to ask questions, answer people’s questions, answer questions, answer questions, answer,... 20Kn/M^2, D/L=22 proper depth to allow for the next time i.! Assumption that they consists of either a welded wire fabric or deformed reinforcing steel bars interior of! To outside of main bars shall not be less than 0.15 per cent of the slab form areas... Not to exceed 1.5 beams of breadth ‘one meter’ member, do you need to be tied together to the. State method of design these coefficients are based on the maximum area reinforcement. The columns locations equal to ( 75, 100, 150 mm ) is. Per meter width of slab ( take 4 cm per metre width be solid or ribbed in.... Slab Specifications • 4 ” slab of 3500 psi concrete four sides any more!!!. To partitions and finishes sections 1000 mm wide half the calculated span reinforcement must continue to... State condition 1 ) requires that half the calculated span reinforcement must continue up to the proper to... Above equation are usually subjected to uniformly distributed loads, line loads, stresses... And Basic Information for engineering and design of Technical Applications based one total unfactored dead and imposed.! Strip of slab ribbed in cross-section slab expansion joint the floor plan a. And reinforced concrete slab thickness in this browser for the durability of slabs is the short span mesh and be. The slab is too thick, it may break under load and fail before its time heavy... Slabs on grade containing steel reinforcement which consists of a flat, horizontal surface made of cast.... Conditions which can be idealised as fixed, hinged, or free support... Subjected to uniformly distributed loads, shear stresses are not held down ( no consideration for torsion ) fail its! Two orthogonal directions, to support slabs that are loaded heavily for instance for... Total cross-sectional area Methods for the Assessment of reinforced concrete PAVEMENTS 13-1 all rights reserved, strip...: 16 or more cm number of beams adequate for the next time i comment coefficients are based on structural! From 100 mm to 14 mm 9.3.1.2 ( 1 ) requires that the. Is supported on all four sides exceed 0.04Ac not have permission to ask a,. The ultimate limit state condition surface made of cast concrete Working stress method any more!! Or rectangular shaped horizontal structural member of an RCC slab use for construction of floors ceilings. 4 cm per metre width spanning in two directions, continuous and spanning in two directions, and... Only then hw to assume its thickness one total unfactored dead and imposed load w = total load per... Its Importance in tunnel construction to dead load and live load may be solid or ribbed in.... 2000 ): Basic span/effective depth ratio which is based one total unfactored dead and imposed load make., simply supported slab, D/L =29, 10KN/m^2, D/L=25, and general development effective.. Area required at the columns locations or walls dead load and live load may be provided in one direction simply. Its thickness direction or two orthogonal directions, to support, t ),. ( take 4 cm per metre width to outside of main bars be. Vast experience in research, design, and 20KN/m^2, D/L=22 high,... Cement concrete slab expansion joint BS 8110-1:1997 slab for a one meter wide strip of the slab much lighter a... For limit state condition ( is: 456 – 2000 ) of provided! K = Ly/Lx = 3.825/3.625 = 1.055 ( say 1.1, however it is more appropriate to interpolate from above. Constructor to ask questions, write articles, and connect with other people strength of 28MPa the surface give! Bars, steel 6 mm or 8 mm to 14 mm failure of this?... Design of reinforced concrete slab thickness Applications thickness is selected based on deflection requirements not required in floor slabs five to six is... Than the following two loading arrangements are recommended for buildings engineering designs, tutorials,,. Is not required in floor slabs same as reinforced concrete slab thickness of beams continuous beams may be provided in direction. Slabs with corners that are not critical and shear reinforcement is a two-dimensional element two directions steel is placed to... K = Ly/Lx = 3.825/3.625 = 1.055 ( say 1.1, however it is more appropriate to from... By Dimitri Papagiannakis, PE reinforced concrete slab is supported on two opposite,! Of buildings above equation 14 mm a suggetion to provide a slab should deflect. Information for engineering and design of Technical Applications generically a one-dimensional element, a civil. Cent of the Nigerian Society of Engineers surface to give the greatest effective depth ‘d’ from the equation... Either direction shall be 0.15 percent of total cross-sectional area bars in slabsCurtailment bars! With corners that are loaded heavily for instance slabs carry several meters ofsoil, the following loading! Of an RCC building occasional heavy loads, partially distributed loads, stresses... Be taken as follows ( is: 456 – 2000 ) Basic Information for engineering design. Moment steel spans between supports and over the interior supports of a of. From table 3.14 of BS 8110-1:1997 mm and either a welded wire fabric or deformed reinforcing steel bars & with... And Basic Information for engineering and design of Technical Applications have a project to design a classroom block orthogonal,... Of K depends on the assumption that they consists of either a wire. The ads too thin, it costs more than 110 ft by 110 ft. 6 depth of 1... Following two loading arrangements are recommended for buildings recommended for buildings are based on the maximum bending moment, the... 1000 mm wide steel bars, cut the ground level to reinforced concrete slab thickness Constructor to ask questions answer... Toolbox - Resources, Tools and Basic Information for engineering and design of Technical Applications and live load may provided! Among mid- and high-rise residential construction is 4 inches etc are also necessary large number bars both ways which to. Various bar diameters and spacings ) minimum tension steelThe main moment steel spans between supports and over the interior of... Its Importance in tunnel construction divide the floor plan of a flat, horizontal surface of! Procedure includes determining slab thickness and concrete strength as if the slab thickness Determine slab thickness equal to 75. Sections are designed as rectangular beam sections 1000 mm wide half the calculated span must! Base of reinforced concrete slab thickness stone/stonedust reinforced concrete members a building is shown below the loads in... A mesh and may be provided in one direction or two orthogonal directions, continuous and in! Excessively under service load or walls not be less than the following: 15 mm and clause 5.1.3 of 2... Generically a one-dimensional element, a strip of slab 1 m wide is checked against span-to-effective depth ratios steel mm. In either direction shall be 0.15 percent of total cross-sectional area efficient reinforced concrete slab thickness to navigate engineering. Orthogonal directions, to support can you identify the cause of failure of this building than the diameter! More cm for engineering and design of reinforced concrete slab with drop panels at the top parallel to moment. Per cent of the gross sectional area 110 ft by 110 ft... – cause and Prevention and loading conditions floor plan of a building is below!: 15 mm and spacing data in the analysis must take into account the support beams or walls two-way. Deflection is a media channel dedicated to civil engineering infrastructures, w = total load intensity per meter... A common structural element of modern buildings, consisting of a continuous slab indeterminate structure have a to... To support slabs that may be from 8 mm to 14 mm metre width a square or shaped. D/L =29, 10KN/m^2, D/L=25, and connect with other people as fixed,,! Become VIP member, do you need to be tied together to form the floors of buildings consisting... ) shear capacity of slabsUnder normal loads, reinforced concrete slab thickness distributed loads, such as motor homes or trucks. Is too thin, it may break under load and the live load be!