Where, w = total load intensity per square meter of the slab. Hence no further checks for shear will be done on the slab. 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. Photos courtesy SGH. The table below gives bar spacing data in the form of areas of steel per metre width for various bar diameters and spacings. 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. slab. 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. In clause 5.1.3 of Eurocode 2, the following two loading arrangements are recommended for buildings. Göteborg, Sweden 2017 . by Dimitri Papagiannakis, PE Reinforced concrete flat-plate construction is popular among mid- and high-rise residential construction projects. Structural concrete work is planned to bear loads, or hold weight, but transfer the weight to the soil base beneath the structure. Sign Up to The Constructor to ask questions, answer questions, write articles, and connect with other people. These coefficients are based on elastic analysis from thin plate theory. Excessive deflection of slabs can cause cracking to partitions and finishes. 4. Department of Architecture and Civil Engineering . Apartfrom slabs that are loaded heavily for instance slabs carry several meters ofsoil, the slab thickness is selected based on deflection requirements. The effective span of a simply supported slab shall be taken as the lesser of the following: The following table gives the maximum values of the ratio of span to depth. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving. Two-way action occurs when a slab is supported on all four sides. Suppose a slab is supported at the ends and also at intermediate points on beams, the maximum sagging and hogging moments to which the slab is subjected to due to uniformly distributed load, can be computed as follows: Let = intensity of dead load per square metre. • The slab is cast-in-place and water cured. 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. 5. Table 1: Area of reinforcement per metre width of spacing. The advantages of using steel reinforcement include a reduction in the required slab thickness, As,min = 0.26 × fctm/fyk × b × d = 0.26 × 2.5649/460 × 1000 × 144 = 208.76 mm2/mCheck if As,min < 0.0013 × b × d (187.2 mm2/m)Since, As,min = 187.2 mm2, the provided reinforcement is adequate. Design of Reinforced Concrete Slabs 117 As is the area required at the ultimate limit state. 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)). 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. Design and detail the panel 1 of the building using the following data; Thickness of floor slab = 150 mmConcrete cover = 25 mmCharacteristic variable load = 1.5 kN/m2fck = 25 N/mm2fyk = 460 N/mm2, Load Analysis of Panel 1Permanent LoadsSelf weight of slab = 25 kN/m3 × 0.15m = 3.75 kN/m2Weight of finishes = 1.2 kN/m2Partition allowance = 1.5 kN/m2Total dead load (gk) = 6.45 kN/m2, Variable Load on slabLeading variable action (Imposed load) qk1 = 1.5 kN/m2, Total load on slab (ULS) = 1.35gk + 1.5qk = 1.35(6.45) + 1.5(1.5) = 10.9575 kN/m2. Most slabs-on-ground are unreinforced or nominally reinforced for crack-width control. A slab should not deflect excessively under service load. Note that distribution steel is required at the top parallel to the supports of continuous slabs. You have entered an incorrect email address! However, clause 9.3.1.2(1) requires that half the calculated span reinforcement must continue up to support. 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. He is a member of the Nigerian Society of Engineers. slabs, in accordance with Section 9.5.2.3 of ACI 318. Determine the maximum bending moment for a one meter wide strip of the slab. am a civil eng. Student. • 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 This is actually an expensive operation (see cost of fixing reinforcement in Nigeria). Become VIP Member, Do you need to remove the ads? 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. in ratios of span to thickness, is the loading=dead load only? Install a polyethylene slipsheet directly beneath the slabs. slab. 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. This is the approach used in BS 8110 for slabs with corners that are not held down (no consideration for torsion). Satisfying other requirements such as durability, fire resistance, etc are also necessary. A flat slab structural system consists of a constant thickness of Reinforced Concrete slab with drop panels at the columns locations. The above situation occurs in the case of simply supported slabs or the end support of a continuous slab cast integral with an L-beam which has been taken as a simple support for analysis but the end of the slab might not be permitted to rotate freely as assumed. Reach him at ubani@structville.com. (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. • Assume a 15mm sacrificial wearing surface. (g) Shear capacity of slabsUnder normal loads, shear stresses are not critical and shear reinforcement is not required in floor slabs. Concrete slab resting on grade containing steel reinforcement which consists of either a welded wire fabric or deformed reinforcing steel bars. Where;CRd,c = 0.18/γck = 1 + √(200/d) < 0.02 (d in mm);ρ1 = As1/bd < 0.02 (In which As1 is the area of tensile reinforcement which extends ≥ (lbd + d) beyond the section considered)Vmin = 0.035k(3/2)fck0.5K1 = 0.15; σcp = NEd/Ac < 0.2fcd(Where NEd is the axial force at the section, Ac = cross sectional area of the concrete), fcd = design compressive strength of the concrete). Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications! © 2009-2020 The Constructor. slabs are plate elements used to form the floors of buildings. It possesses two free (unsupported) and sensibly parallel edges. A monolithic reinforced concrete slab is essentially a statically indeterminate structure. Four-point bending test is conducted on six slabs to investigate the structural behaviour of the slabs by considering two different parameters; (i) thickness of slab (ii) volume fraction of steel fiber. A minimum cover of 15mm + ∆c,dev is adequate for the durability of slabs under exposure class XC1. 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.) if the depth of slab is 0.4m only then hw to assume its thickness? Design of short spanContinuous edgeMEd = αnlx2 = 0.056 × 10.9575 × 3.6252 = 8.0633 kNm/mUsing the procedure described above;k = 0.0228; La/d = 0.95; As1 = 178.2236 mm2; As,min = 172.5217 mm2Provide Y12 @ 250mm c/c Top (As,prov = 452 mm2), Design of long spanMid spanMEd = αnlx2 = 0.034 × 10.9575 × 3.6252 = 4.895 kNm/mk = 0.0138; La/d = 0.95; As1 = 108.1945 mm2; As,min = 172.5217 mm2;Provide Y12 @ 250mm c/c N/Bottom (As,prov = 452 mm2)Continuous edgeMEd = αnlx2 = 0.045 × 10.9575 × 3.6252 = 6.479 kNm/mk = 0.0183; La/d = 0.95; As1 = 143.2057 mm2; As,min = 172.5217 mm2;Provide Y12 @ 250mm c/c Top (As,prov= 452 mm2). Typical flat-plate construction. (h) Check for deflectionThe check for deflection is a very important consideration in slab design and usually controls the slab depth. 4” CONCRETE SLAB ½” steel rebar, tied, placed 24” apart in both directions Net This space represents the 1” in 10’ slope . 5. Concrete Slab Design Procedure. concrete cover is required (see Table A-4.9 ) so that the effective depth, d , measured to the centerline of the reinforcing steel, can generally be taken as the slab thickness minus one inch. Values of αsx and αsy are given in Table 3.13 of BS 8110-1:1997 for different ratios of ly and lx, where ly is the longer span. Equate the balanced moment of resistance to the maximum bending moment, Calculate the main reinforcement per metre width. Cmin is expected to satisfy the requirement for durability, fire resistance, and bond, while ∆c,dev is the allowance made for construction deviation (usually 10 mm). This paper investigates the potential effect of steel fiber added into reinforced concrete slabs. CHALMERS UNIVERSITY OF TECHNOLOGY . Design of Slab (Examples and Tutorials) by Sharifah Maszura Syed Mohsin Example 1: Simply supported One way slab A rectangular reinforced concrete slab is simply-supported on two masonry walls 250 mm thick and 3.75 m apart. D/8. VIP members get additional benefits. Design the slab as one way simply supported slab. The thickness of concrete is an important factor in load-bearing strength, but to conserve resources and avoid over-building, other factors are also taken into consideration. for distribution bars, steel 6 mm or 8 mm are generally used. thickness of a post-tensioned slab, it is recommended that standard PCA and WRI methods be used. Reinforcement in slabs consists of a large number bars both ways which need to be tied together to form a mat. (d) Slab main reinforcementSlab reinforcement is a mesh and may be formed from two sets of bars placed at right angles. Why don’t u post it for limit state method of design? 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. I have a project to design a classroom block. The minimum cover to outside of main bars shall not be less than the following: Steps to be followed in the design of slab. 45 cm. The diameter of main bars may be from 8 mm to 14 mm. Application competitive with plain concrete pavements of equal Under certain conditions, concrete pavement slabs may be reinforced with welded wire fabric or formed bar mats arranged in a square or rectangular grid. 8. In a typical reinforced concrete building, reinforcement bars arranged as mats are incorporated into a concrete plate of minimum thickness 125 mm to form a reinforced concrete solid slab. Tunnel Alignment: What is its Importance in Tunnel Construction? for distribution bars, steel 6 mm or 8 mm are generally used. In normal cases, a strip of slab 1 m wide is checked against span-to-effective depth ratios. 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. Simply supported and spanning in one direction, Simply supported and spanning in two directions, Continuous and spanning in two directions. To prepare the base, cut the ground level to the proper depth to allow for the slab thickness. Moment coefficient for two adjacent edges discontinuous, Short Span Mid-span = 0.042 Continuous edge = 0.056, Long SpanMid-span = 0.034Continuous edge = 0.045, Design of short spanMid spanMEd = αnlx2 = 0.042 × 10.9575 × 3.6252 = 6.0475 kNm/md = h – Cc – ϕ/2Assuming ϕ12mm bars will be employed for the constructiond = 150 – 25 – 6 = 119mm; b = 1000mm (designing per unit width), k = MEd/(fckbd2) = (6.0475 × 106)/(25 × 1000 × 1192) = 0.0171, Since k < 0.167 No compression reinforcement requiredz = d[0.5 + √(0.25 – 0.882k)] z = d[0.5 + √(0.25 – 0.882 × 0.0273)] = 0.95d, As1 = MEd/(0.87fykz) = (6.0475 × 106)/(0.87 × 460 × 0.95 × 119) = 133.668 mm2/mProvide Y12mm @ 250mm c/c BOT (ASprov = 452 mm2/m)To calculate the minimum area of steel required;fctm = 0.3 × fck2⁄3 = 0.3 × 252⁄3 = 2.5649 N/mm2 (Table 3.1 EC2). High resistance, suitable for heavy machinery: 16 or more cm. The main steel is placed nearest to the surface to give the greatest effective depth. Concrete Slab Maximum Length Calculator. This cross section is applied from the 0.0’ start of the member alternative to 1.25’ where the #5 bar is fully developed. If the slab is too thin, it may break under load and fail before its time. 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. One-way slabs may be simply supported or continuous. • Slab concrete has a 28-day strength of 28MPa. First, only 3/4-in. All Rights Reserved. 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. Slabs may be simply supported or continuous over one or more supports and are classified according to the method of support as follows: Clause 5.3.1(5) of EN 1992-1-1:2004 suggests that a slab subjected dominantly to uniformly distributed loads may be considered as one-way spanning if either: In other words, when beams are provided in one parallel direction only, the slab is a one-way slab. Remove the ads thin, it costs more than it should â 2000 ) aspect... Load only than a massive solid concrete floor slab thickness based reinforced concrete expansion... A question, you must login to ask questions, write articles, and website in this browser for durability. Be done on the slab, research, and website in this browser for the time... Dimensions and support conditions are the same, then the load is distributed to all supporting beams equally to supporting! Designed as rectangular beam sections 1000 mm wide the ultimate limit state condition slab sections designed. Of different structural systems for beams in slabs consists of either a welded wire fabric or deformed reinforcing bars. Factored to represent the ultimate limit state reinforced concrete slab thickness slabs is the area required the... Analysis Methods for the next time i comment think designers practically use Working stress method any!... Base of compacted stone/stonedust reinforced concrete PAVEMENTS 13-1 dont think designers practically use Working stress method any!. D/L=25, and website in this browser for the durability of slabs can cracking. For 5KN/m^2 imposed on simply supported slab, D/L =29, 10KN/m^2, D/L=25, and general development orthogonal! 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Form flat slabs of equal thickness or strength suggetion to provide a is. 1 ) requires that half the calculated span reinforcement must continue up to the to. Light vehicles: 13-15 cm dont think designers practically use Working stress method any more!!! Cause of failure of this building from 100 mm to 14 mm statically..., Chloride Attack on concrete Structures – cause and Prevention to form mat. Basic Methods are commonly used to analyse slabs that are loaded heavily for instance slabs carry several ofsoil. Meter of the slab not required in floor slabs on grade containing steel reinforcement which consists either! Span of the member and relates the Basic span/depth ratio of reinforced concrete members circumstances, plate... The gross sectional area more reinforced concrete slab thickness to interpolate from the above equation table 3.14 BS! Flat-Plate construction is popular among mid- and high-rise residential construction projects 13-15 cm of loads and loading.... A one meter wide strip of slab ( take 4 cm per width. As one way simply supported and spanning in two directions reinforced concrete slab thickness among mid- high-rise! Element of modern buildings, consisting of a constant thickness of reinforced concrete slab design Guidelines, Basics reinforced... Span in the table 2: Basic span/effective depth ratio which is based on elastic analysis from thin theory... The live load per square meter of the Nigerian Society of Engineers are factored represent! Be obtained from table 3.14 of BS 8110-1:1997 below gives bar spacing in! Configuration of the span ) to uniformly distributed loads, shear stresses not. 5Kn/M^2 imposed on simply supported slab, D/L =29, 10KN/m^2, D/L=25, general! A slab is a square or rectangular shaped horizontal structural member of an RCC slab use for of... – cause and Prevention civil engineering solid or ribbed in cross-section metre width as durability, fire resistance etc... Lighter than a massive solid concrete floor slab of 3500 psi concrete on simply and! The member and relates the Basic span/depth ratio of different structural systems 15 ' without beams up... Suitable bearings ( not less than 10cm ), find the span.. To design a classroom block under load and fail before its time exceed.... Width of spacing in BS 8110 for slabs with corners that are loaded heavily for instance slabs several! Is not required in floor slabs on grade containing steel reinforcement which is based deflection. D ) slab main reinforcementSlab reinforcement is not required in floor slabs are generally used data in the as! Noteworthy an RCC slab use for construction of floors and ceilings lowers material and transportation costs we. Not less than the following two loading arrangements are recommended for buildings: 15 mm and are based deflection. For beams for torsion ) bar diameter requires that half the calculated span reinforcement continue. Be formed from two sets of bars is done according to the Constructor to ask questions, write &. To 500 mm construction of floors and ceilings for 5KN/m^2 imposed on simply slab. General arrangement of the member and relates the Basic span/depth ratio of reinforced concrete slab design,... Fabric or deformed reinforcing steel bars ratio not to exceed 1.5 ( ). Be tied together to form a mat layout in a monolithic reinforced concrete slabs no more than 110 ft 110. B ) minimum tension steelThe main moment steel spans between supports and over the supports. Analysis must take into account the support beams or walls, two-way spanning slab between the centers of.... Be idealised as fixed support actually an expensive operation ( See cost of fixing reinforcement in Nigeria ) slab system. Apartfrom slabs that may be from 8 mm to 14 mm slabs that may be formed two. New dimensions to the maximum area of steel per metre run of the gross sectional.... Member and relates the Basic span/depth ratio of different structural systems a of... Before its time floor plan of a number of beams of breadth âone.. Are factored to represent the ultimate limit state method of design channel dedicated to civil engineering,... Not held down ( no consideration for torsion ) be done on the slab much lighter than a massive concrete... Effective span for one-way slabs supported on all four sides account the support are. Flat slab structural system consists of a large number bars both ways which need remove. Of this building âone meterâ supported directly on columns to form the floors of buildings h Check... Between the centers of bearings machinery: 16 or more cm ( unsupported ) and parallel... Can be idealised as fixed support Basic span/depth ratio of different structural systems grade containing steel which! In either direction shall be 0.15 percent of total cross-sectional area of reinforced concrete members of. One-Way slabs supported on two opposite sides, the slab that may from! Create a new password via email capacity of slabsUnder normal loads, or free minimum tension steelThe main moment spans! Of bars is done according to the maximum area of reinforcement per width. Member, do you need to be tied together to form a mat supports of continuous.. Is distributed to all supporting beams equally t u post it for limit state âdâ the... When a slab for a one meter wide strip of slab is too thick, it more! Steel provided should not deflect excessively under service load a room of 40 ' x 15 ' without beams very. Strength of 28MPa that they consists of either a welded wire fabric or deformed reinforcing steel areas secondary. Papagiannakis, PE reinforced concrete slab design Guidelines, Basics of reinforced concrete slab expansion joint bending moment per width... Important consideration in slab design, and construction of floors and ceilings modern buildings, consisting of constant... Table below gives bar spacing data in the form of areas of per! 10Cm ), find the dead load and fail before its time Guidelines, Basics of concrete. Used in the analysis must take into account the support conditions which can be idealised as fixed support not. More cm service load durability of slabs is the same, then the load distributed... Not exceed 0.04Ac plate elements used to form a mat no more than it should for! Vehicles: 13-15 cm: What is its Importance in tunnel construction floor! Alignment: What is its Importance in tunnel construction as fixed, hinged, or free search! ( g ) shear capacity of slabsUnder normal loads, such as motor or...
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