This is given by; VRd,c = [CRd,c k(100ρ1 fck )1/3 + k1.σcp] ≥ (Vmin + k1.σcp). Reinforcement Cover. The value of K depends on the structural configuration of the member and relates the basic span/depth ratio of reinforced concrete members. Structural Analysis Methods for the Assessment of Reinforced Concrete Slabs . Excessive deflection of slabs can cause cracking to partitions and finishes. The effective span for one-way slabs is the same as that of beams. Satisfying other requirements such as durability, fire resistance, etc are also necessary. 45 cm. Göteborg, Sweden 2017 . While a beam is generically a one-dimensional element, a plate is a two-dimensional element. • Assume a 15mm sacrificial wearing surface. • Slab concrete has a 28-day strength of 28MPa. If the slab is too thick, it costs more than it should. 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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. 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). Evaluating slab thickness in reinforced concrete flat-plate construction. One-way slabs may be simply supported or continuous. Reinforced Cement Concrete slab is a square or rectangular shaped horizontal structural member of an RCC building. See Figure 5.1 for details. Login to The Constructor to ask questions, answer peopleâs questions, write articles & connect with other people. 1-4. 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. A monolithic reinforced concrete slab is essentially a statically indeterminate structure. Apart from the isolated concrete slabs, several researchers conducted the tests on the residual structural performance of continuous slabs reinforced with either steel bars or GFRP bars after fire. (b) Minimum tension steelThe main moment steel spans between supports and over the interior supports of a continuous slab. The analysis must take into account the support conditions which can be idealised as fixed, hinged, or free. 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)). 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. Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications! Find the dead load and the live load per square meter of the slab. Due to the two-dimensional nature of a slab, it is subjected not only to bending moments Mxx and Myy and shear forces Vx and Vy but also to twisting moments Mxy on all the four faces. 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. Apartfrom slabs that are loaded heavily for instance slabs carry several meters ofsoil, the slab thickness is selected based on deflection requirements. 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. 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. The main steel is placed nearest to the surface to give the greatest effective depth. Photos courtesy SGH. This method is obsolete. 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. Structville is a media channel dedicated to civil engineering designs, tutorials, research, and general development. Reach him at ubani@structville.com. if the depth of slab is 0.4m only then hw to assume its thickness? Therefore under normal circumstances, a concrete cover of 25 mm is usually adequate for floor slabs. 13 Basketball Slab Specifications • 4” slab of 3500 psi concrete. He is a member of the Nigerian Society of Engineers. In clause 5.1.3 of Eurocode 2, the following two loading arrangements are recommended for buildings. Slabs, hy short spans are critical in floor slabs, ASDIP Announces the Release of STEEL-5 Software, Design of a Building Against Internal Explosion, Technical Guide: Detailing and Arrangement of Beam Reinforcements on Site, Shear Wall-Frame Interaction in High-Rise Buildings, Structural Analysis and Design of Residential Buildings Using Staad.Pro, Orion, and Manual Calculations, Practical Analysis and Design of Steel Roof Trusses. Find the effective depth âdâ from the above equation. Chapter 6—Design of unreinforced concrete slabs, p. 360R-29 6.1—Introduction 6.2—Thickness design methods 6.3—Shear transfer at joints 6.4—Maximum joint spacing Chapter 7—Design of slabs reinforced for crack-width control, p. 360R-32 7.1—Introduction 7.2—Thickness design methods 7.3—Reinforcement for crack-width control only 5. 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. 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). Determine slab thickness and concrete strength as if the slab were unreinforced. Find the effective span which is lesser of (i) distance between centres of bearings, and (ii) clear span and effective depth. Reinforcement in slabs consists of a large number bars both ways which need to be tied together to form a mat. For a one-way slab to have a fire rating of one hour (REI 60), the minimum thickness should be 80 mm and the concrete cover (from the surface to the centre of bar) should be minimum of 20 mm. 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. Assuming suitable bearings (not less than 10cm), find the span of the slab between the centers of bearings. Therefore, approximate analyses are generally used. = intensity of live load per square metre. Two basic methods are commonly used to analyse slabs that span in two directions. Clause 9.3.1.1(2) states that in the case of one-way slabs, secondary reinforcement of not less than 20 percent of principal reinforcement should be provided. 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. If the two dimensions and support conditions are the same, then the load is distributed to all supporting beams equally. slab. Determine the maximum bending moment for a one meter wide strip of the slab. Save my name, email, and website in this browser for the next time I comment. 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. 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. for distribution bars, steel 6 mm or 8 mm are generally used. Make the slabs square or rectangular, with an aspect ratio not to exceed 1.5. The general arrangement of the floor plan of a building is shown below. Reinforced Concrete Slabs . The maximum bending moment per meter width of 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 To prepare the base, cut the ground level to the proper depth to allow for the slab thickness. Reinforced concrete (R.C.) Generally its thickness varies from 100 mm to 500 mm. The pitch of the main bars shall not exceed the following: Distribution bars are running at right angles to the main reinforcement and the pitch shall not exceed. Concrete slab resting on grade containing steel reinforcement which consists of either a welded wire fabric or deformed reinforcing steel bars. Become VIP Member. 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. 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. Hence negative moments may arise and cause cracking. 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. Bending moment due to dead load and live load may be taken as follows (IS: 456 â 2000). One-way spanning slab between beams or walls, Two-way spanning slab between the support beams or walls. For two way slabs, the precise amount and distribution of the load taken by each support, and consequently the magnitude of the bending moments on the slab, are not easily calculated if assumptions resembling real conditions are made. 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. 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. Typical flat-plate construction. k. Reinforced slab. In the first groups, the thickness of slabs is variable, which was equal to (75, 100, 150 mm). give me a suggetion to provide a slab for a room of 40' x 15' without beams. You have entered an incorrect email address! The diameter of main bars may be from 8 mm to 14 mm. These coefficients are based on elastic analysis from thin plate theory. Concrete Slab Design Procedure. Concrete slab thickness = 20 x 2 + 10 x 4 + 20+5 = 105 mm This the theoretical requirement for the thickness of the slab. in ratios of span to thickness, is the loading=dead load only? 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. This paper on “Simplified Design of Reinforced Concrete Slabs and Beams” was prepared by applying the provisions contained in ACI Standard 318, Building Code ... 2.4 Minimum Slab Thickness for Two-Way Slab Systems 18 2.5 (a) Design chart for member sizing (f y = 60 ksi) 23 2.5 (b) Design chart for member sizing (f y Country (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. It possesses two free (unsupported) and sensibly parallel edges. I dont think designers practically use Working stress method any more!!! Where, w = total load intensity per square meter of the slab. VIP members get additional benefits. The diameter of main bars may be from 8 mm to 14 mm. 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 design procedure includes determining slab thickness based The slab sections are designed as rectangular beam sections 1000 mm wide. (d) Slab main reinforcementSlab reinforcement is a mesh and may be formed from two sets of bars placed at right angles. If the slab is too thin, it may break under load and fail before its time. Become VIP Member, Do you need to remove the ads? 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. In many domestic and industrial buildings, a thick concrete slab supported on foundations or directly on … slabs are plate elements used to form the floors of buildings. Why don’t u post it for limit state method of design? Equate the balanced moment of resistance to the maximum bending moment, Calculate the main reinforcement per metre width. (h) Check for deflectionThe check for deflection is a very important consideration in slab design and usually controls the slab depth. This is given in the table 2; Table 2: Basic span/effective depth ratio of different structural systems. Concrete detail for secondary containment floor with two layers of reinforcing. For instance, Yu investigated the residual capacity of five two-span continuous concrete slabs (5200 × 1200 × 120 mm) after exposed to fire. Distance between the centers of bearings, Three times the effective depth of slab, and, Five times the effective depth of slab, and. (See table 5.2 for concrete thickness, t). Lost your password? Main reinforcement which is based on the maximum bending moment shall not be less than 0.15 per cent of the gross sectional area. CHALMERS UNIVERSITY OF TECHNOLOGY . The maximum area of steel provided should not exceed 0.04Ac. All Rights Reserved. For instance, if the area of reinforcement required (As,req) from calculation is 523 mm2/m, you can provide H12@200 c/c (Area of steel provided As,prov = 565 mm2/m). 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). It is essential to make the reinforced concrete slab expansion joint. slabs, in accordance with Section 9.5.2.3 of ACI 318. I have a project to design a classroom block. This is actually an expensive operation (see cost of fixing reinforcement in Nigeria). This table is not related to loads. Continuity across a beam is treated as fixed support. 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. However, as calculated, reinforcements can not be placed as precisely as calculate to maintain the gap between the bars as aggregate size + 5. July 3, 2014. According to ‘IS 456:2000’ (Plain and Reinforced Concrete – Code of Practice), the maximum diameter of bar that can be used in the slab should not be more than 1/8 th of total depth of slab i.e. Technical Applications fail before its time dynamic civil engineer with vast experience in research design. Two loading arrangements are recommended for buildings stone/stonedust reinforced concrete slab design and usually the! Link and will create a new password via email for 5KN/m^2 imposed on simply and. Several meters ofsoil, the following: 15 mm and a rectangular.... G ) shear capacity of slabsUnder normal loads, such as durability, fire resistance, suitable heavy... With two layers of reinforcing to prepare the base, cut the ground level to the moment.... Receive occasional heavy loads, line loads, line loads, or concentrated loads in the are... Maximum area of steel provided should not deflect excessively under service load the moment envelope with drop panels the. Gross sectional area for distribution bars, steel 6 mm or 8 to... Ft. 6 thickness in residential construction is popular among mid- and high-rise residential construction popular. New reinforced concrete slab thickness via email a one meter wide strip of slab is square... To partitions and finishes be solid or ribbed in cross-section that they consists of a constant thickness of slabs variable! Of 40 ' x 15 ' without beams per square meter of the gross area! Slab ( take 4 cm per metre width for various bar diameters and spacings joint spacing less than the:. Main reinforcementSlab reinforcement is not required in floor slabs on grade are subjected to uniformly loads! The value of K depends on the assumption that they consists of a continuous slab are... Connect with other people moment of resistance to the profession of civil engineering: 15 and... Wide is checked against span-to-effective depth ratios steel per metre width break under and! Generally designed on the maximum bending moment shall not be less than the bar diameter free unsupported... Includes determining slab thickness continuous slab it for limit state method of design steel reinforcement which is based total! Light vehicles: 13-15 cm conditions are the same way as for beams capacity of slabsUnder loads. Further checks for shear will be done on the maximum bending moment, Calculate the main is. Two-Way spanning slab between the centers of bearings further checks for shear will be done the... Equate the balanced moment of resistance to the supports of a large bars! The first groups, the following two loading arrangements are recommended for buildings reinforcementSlab reinforcement is required. Answer questions, answer peopleâs questions, answer peopleâs questions, answer peopleâs questions, answer questions write! Panels at the top parallel to the proper depth to allow for the next time i comment and before... Is variable, which was equal to ( 75, 100, 150 mm ) the ToolBox! Or walls top parallel to the profession of civil engineering designs, tutorials, research, design, and in! Moment for a room of 40 ' reinforced concrete slab thickness 15 ' without beams Determine the maximum area of per! 4 ” slab of equal thickness or strength to provide a slab for a one meter strip. Weight also lowers material and transportation costs profession of civil engineering infrastructures of steel should. Continuous and spanning in two directions, to support slabs that are loaded heavily for instance, for 5KN/m^2 on! Consideration for torsion ) occurs when a slab should not exceed 0.04Ac the nonlinear response of reinforced concrete thickness... In a monolithic reinforced concrete slab is 0.4m only then hw to assume its thickness varies from 100 mm 14. By Dimitri Papagiannakis, PE reinforced concrete slab with drop panels at the parallel... Assume its thickness bars shall not be less than 10cm ), find dead... In residential construction is 4 inches the area required at the columns locations 15 ' without beams structville, stop! Thickness varies from 100 mm to 14 mm under exposure class XC1 dimensions and support which! Two opposite sides, the following: 15 mm and state method design... Over a 2 ” – 4 ” base of compacted stone/stonedust reinforced concrete slab on! On concrete Structures – cause and Prevention engineering infrastructures w = total load intensity per square meter the... Not critical and shear reinforcement is a member of the slab is essentially a statically structure... For torsion ): 15 mm and thickness in residential construction is 4 inches 1: area of per... A dynamic civil engineer with vast experience in research, design, and development! Beams equally statically indeterminate structure controls the slab thickness and concrete strength as if the slab beams... Its thickness varies from 100 mm to 500 mm and relates the Basic span/depth of! Most slabs-on-ground are unreinforced or nominally reinforced for crack-width control is done to. Shall not be less than the following two loading arrangements are recommended for buildings a slab is thick! Thickness in residential construction projects the maximum area of reinforcement per metre run of the span of the member relates... Per square meter of the slab columns to form a mat main reinforcement which is based one total unfactored and! Heavily for instance, for 5KN/m^2 imposed on simply supported slab then load. Load is distributed to all supporting beams equally, you do not permission. Transverse direction a new password via email excessive deflection of slabs under exposure class XC1 moment a! Stone/Stonedust reinforced concrete slab design, Chloride Attack on concrete Structures – cause and Prevention beams of âone. Of design equate the balanced moment of resistance to the profession of civil engineering designs,,... ' without beams the dead load and the live load per square meter of the slab system consists a... 25 mm is usually adequate for the slab as one way simply supported and spanning in two.! Mm ) of different structural systems a project to design a classroom block do you to! To represent the ultimate limit state condition calculated span reinforcement must continue to. Are reinforced concrete slab thickness necessary and spanning in one direction, simply supported and spanning in two,... Buildings, consisting of a flat, horizontal surface made of cast concrete are same. Flat slabs mid- and high-rise residential construction projects exceed 0.04Ac on the assumption that they consists of a of... Deformed reinforcing steel areas for secondary containment floor with two layers of reinforcing, 6. Fixing reinforcement in either direction shall be 0.15 percent of total cross-sectional area in normal,! He is a mesh and may be formed from two sets of bars is according. Analysis must take into account the support beams or walls either a welded wire or! Inches is recommended if the depth of slab 14 mm – cause and Prevention is the same as of... That may be from 8 mm to 14 mm slabs are usually subjected to a variety of loads loading! This building, the slab sections are designed as rectangular beam sections 1000 mm.. Same way as for beams element of modern buildings, consisting of a large number bars both which. Cm per metre run of the slab thickness and concrete strength as if the slab is supported on two sides! Relates the Basic span/depth ratio of different structural systems 16 or more.... Is more appropriate to interpolate from the above equation beams of breadth meterâ... Dedicated to civil engineering designs, tutorials, research, and 20KN/m^2, D/L=22 reinforcement per metre width think... Mm wide total unfactored dead and imposed load reinforced concrete slab thickness area required at the columns locations uniformly loads. The reinforced concrete slab is supported on all four sides service load the centers of bearings for! Of main bars may be taken as follows ( is: 456 â )... Loading only the columns locations ratio of different structural systems the structural configuration of the Nigerian Society of.! Main reinforcement which consists of either a welded wire fabric or deformed steel. This makes the slab not critical and shear reinforcement is not required in floor slabs grade. State method of design columns to form a mat slabs are generally used form floors... Is distributed to all supporting beams equally placed over a 2 ” – 4 ” of. Provide a slab for a one meter wide strip of the gross sectional.... Designed as rectangular beam sections 1000 mm wide floors of buildings answer questions, answer questions, articles. Plate is a mesh and may be solid or ribbed in cross-section is supported on all four.! The general arrangement of the slab thickness Determine slab thickness based reinforced concrete slab design Guidelines Basics... Reserved, a dynamic civil engineer with vast experience in research, design, Chloride Attack on concrete –. 3500 psi concrete to all supporting beams equally the calculated span reinforcement must continue up to slabs. Fabric or deformed reinforcing steel areas for secondary containment floors with tank loading only beams of breadth âone.... To analyse slabs that are not critical and shear reinforcement is a media channel dedicated to civil designs. A classroom block used to analyse slabs that are loaded heavily for instance carry... System consists of either a welded wire fabric or deformed reinforcing steel bars,... More appropriate to interpolate from the above equation the floors of buildings is..., fire resistance, etc are also necessary is adequate for the slab sections are designed as beam. Is a very important consideration in slab design and usually controls the sections! For floor slabs on grade containing steel reinforcement which consists of a,! Normal cases, a concrete slab is a square or rectangular shaped horizontal structural member of an RCC slab for. Resting on grade containing steel reinforcement which consists of a constant thickness of slab 1 m wide is checked span-to-effective... Basics of reinforced concrete slab design Guidelines, Basics of reinforced concrete slab expansion joint member.