The column layout in a monolithic reinforced concrete structure often forms a rectangular grid. The quality of a completed floor slab is dependent on; an appropriate design, the quality of the materials used and the knowledge and experience of the workmen who place and finish the concrete. The maximum diameter of bar used in slab should not exceed 1/8 of the total thickness of slab. Disable spacing conditions. For a flat slab, such as a driveway, consider placing the rebar in an 18 inch grid spacing, keeping the edge rebar at the same distance from each side. 4. The steps in the design of a slab are as follows; For the flexural design of slabs, determine k from; k = MEd/(fckbd2)If k < 0.167, no compression reinforcement is required, and you can calculate the lever arm;z = d[0.5 + √(0.25 – 0.882k)]The area of reinforcement required is given by;As1 = MEd/(0.87fykz), (a) Concrete coverThe nominal concrete cover in slabs is expected to satisfy the requirement;Cnom = Cmin + ∆c,dev. For a patio it is common to use a #3 bar spaced every 18″-24″ while for a driveway #4 bar is often used with a 12″-18″ spacing. Hello All, When deciding the reinforcement type and spacing per foot width in slabs or footings, should you go with larger rebars with larger spacing or smaller rebars with smaller spacing? Hence no further checks for shear will be done on the slab. 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. The maximum area of steel provided should not exceed 0.04Ac. The provision of adequate reinforcement, slab thickness, and proper detailing to satisfy ultimate and serviceability limit state requirements forms the basis of the design of reinforced concrete (R.C.) and please explain why? The coefficients can be obtained from Table 3.14 of BS 8110-1:1997. 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. the maximum spacing between two parallel main reinforcing bars in case of RCC Slab shall be 3d or 300 mm or whichever is less. 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). ACI 360, "Design of Slabs-on-Grade", refers to this as a Type B slab. Thickness of the slab is decided based on span to depth ratio specified in IS456-2000. For a patio you can use a grid spacing of 24 inches. The table below gives bar spacing data in the form of areas of steel per metre width for various bar diameters and spacings. Two-way action occurs when a slab is supported on all four sides. (g) Shear capacity of slabsUnder normal loads, shear stresses are not critical and shear reinforcement is not required in floor slabs. 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. Minimum reinforcement is 0.12% for HYSD bars and 0.15% for mild steel bars. Calculate the Value of ‘D’ (Depth of slab- Top cover- Bottom cover) Find out the No. Concrete Slab Rebar Reinforcement. Can you identify the cause of failure of this building? While a beam is generically a one-dimensional element, a plate is a two-dimensional element. VRd,c = [0.12 × 2 × (100 × 0.003798 × 25)1/3] × 1000 × 119 = 60476.947 N = 60.476 kN Since VRd,c (60.476 kN) > VEd (17.477 kN), no shear reinforcement is required.Note that shear reinforcements are rarely required in solid slabs supported by beams. Rebar Slab: Concrete Cutting Weights ~ Sizes: Core Drill Angles Floor AND Wall: Core Drill Angles Floor OR Wall: Directory: Inch: Inch: Inch: Inch: Inch: Inch: Inch: Calculate Rebar Spacing, Layout and Weight in a Concrete Slab. (e) Crack ControlAccording to Clause 9.3.1.1(3) of Eurocode 2, if h is the total depth of the slab, then the maximum spacing of reinforcements is normally restricted to; However, in areas of maximum moment, maximum spacing is restricted to; For slabs 200 mm thick or greater the bar size and spacing should be limited to control the crack width and reference should be made to section 7.3.3 of the Eurocode 2. Minimum spacing between reinforcement bars in foundation tie-beams Concrete casting in foundation tie-beams is not an easy procedure. A rectangular reinforced concrete slab is simply- supported on two masonry walls 250 mm thick and 3.75 m apart. Hence negative moments may arise and cause cracking. In design, a slab is considered to be two-way if the ratio of the longer side to the shorter side is less than two. 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. Rebar should be placed evenly throughout the project. All Inch inputs and dimensions are actual physical finished sizes, If the US ever goes Metric, you'll be able to use a Meter to measure Meters - A Meter Meter. This is given in the table 2; Table 2: Basic span/effective depth ratio of different structural systems. The diameter of bar generally used in slabs are: 6 mm, 8 mm, 10 mm, 12mm and 16mm. The installation of the rebar is critical for the success of the overall project. 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. Select output Fraction Precision, Decimal Inch or Metric mm. A slab should not deflect excessively under service load. To check the shear capacity of slabs, the shear stress (vEd = VEd/bd) must be checked against the shear capacity of an unreinforced section (VRc,d). This is actually an expensive operation (see cost of fixing reinforcement in Nigeria). (h) Check for deflectionThe check for deflection is a very important consideration in slab design and usually controls the slab depth. You have entered an incorrect email address! The minimum reinforcement will be generated as 1,2 times the area required in ULS verification. The value of K depends on the structural configuration of the member and relates the basic span/depth ratio of reinforced concrete members. Design of Reinforced Concrete Slabs 107 B = 1.2x 1 where x = distance of load-from support closest to load I = effective span. Originally Answered: How much maximum spacing can be given between reinforcement in RCC SLAB? The minimum reinforcement will be generated without limiting the spacing of bars. For vertical stirrups, the maximum spacing of shear reinforcement should not cross 0.75d. Continuity across a beam is treated as fixed support. These coefficients are based on elastic analysis from thin plate theory. With some limitations, reinforcement for slabs can be sized using the Subgrade Drag Theory in order to increase the spacing of control or construction joints. Cover of concrete over/under the reinforcement must be provided to protect the steel from corrosion. according to ACI code 7.6.5 The lateral spacing of temperature and shrinkage reinforcement should not be placed farther apart than 5 times the slab thickness or 18 inch according to ACI code 7.12.2 4. 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. Other considerations 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. Note that distribution steel is required at the top parallel to the supports of continuous slabs. They are; Generally, for rectangular slabs with standard edge conditions and subject to uniformly distributed loads, normally the bending moments are obtained using tabulated coefficients. 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