Paper Reinforced Concrete Slabs

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  • 7/24/2019 Paper Reinforced Concrete Slabs



    Randi Mirah


  • 7/24/2019 Paper Reinforced Concrete Slabs



    Thank to Almighty God who has given His bless to the writer for finishing the paperassignment entitled Reinforced Concrete Slabs The writer also wish to e!press his deepand sincere gratit"de for those who have g"ided in completing this paper

    This paper contains some e!ample of #esign Reinforced Concrete Slabs that can help theviewer to improve knowledge Hopef"lly$ this paper can help the readers to e!pand theirknowledge abo"t Reinforced Concrete Slabs

    %anado$ #ecember &'th$ ()&*


  • 7/24/2019 Paper Reinforced Concrete Slabs



    Reinforced concrete slabs are "sed in floors$ roofs and walls of b"ildings and as the decks

    of bridges The floor system of a str"ct"re can take many forms s"ch as in sit" solid slab$ribbed slab or pre+cast "nits Slabs may span in one direction or in two directions and theymay be s"pported on monolithic concrete beam$ steel beams$ walls or directly by thestr"ct"re,s col"mns

    Contin"o"s slab sho"ld in principle be designed to withstand the most "nfavorablearrangements of loads$ in the same manner as beams -eca"se there are greateropport"nities for redistrib"tion of loads in slabs$ analysis may however often besimplified by the "se of a single load case -ending moment coefficient based on thissimplified method are provided for slabs which span in one direction with appro!imatelye."al spans$ and also for flat slabs

    The moments in slabs spanning in two directions can also be determined "singcoefficients tab"lated in the code of practice$ -S /&&) Slab which are not rectang"lar in

    plan or which s"pport an irreg"lar loading arrangement may be analy0ed by techni."ess"ch as the yield line method or the Helliborg strip method

    Concrete slab behave primarily as fle!"ral members and the design is similar to that forbeams$ altho"gh in general it is somewhat simpler beca"se1

    & the breadth of the slab is already fi!ed and a "nit breadth of &m is "sed in thecalc"lations$

    ( the shear stress are "s"ally low in a slab e!cept when there are heavy concentratedloads$ and

    2 compression reinforcement is seldom re."ired

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    Type of slab "sed in constr"ction sectors are3

    Solid slab 4lat slab Ribbed slab 5affle slab Hollow block floor6slab

    7a8 Solid slab

    7b8 4lat slab

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    7c8 Ribbed slab

    7d8 5affle slab

    4ig"re &3 Types of slab

    4lat slab floor is a reinforced concrete slab s"pported directly by concrete col"mnswitho"t the "se of intermediary beams The slab may be of constant thicknessthro"gho"t or in the area of the col"mn it may be thickened as a drop panel Thecol"mn may also be of constant section or it may be flared to form a col"mn head

    or capital These vario"s form of constr"ction are ill"strated in 4ig"re 2(
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    4ig"re (3 #rop panels and col"mn head

    The drop panels are effective in red"cing the shearing stresses where the col"mnis liable to p"nch thro"gh the slab$ and they also provide an increased moment ofresistance where the negative moments are greatest

    The flat slab floor has many advantages over the beam and slab floor Thesimplified formwork and the red"ced storey heights make it more economical5indows can e!tend "p to the "nderside of the slab$ and there are no beams toobstr"ct the light and he circ"lation of air The absence of sharp corner givesgreater fire resistance as there is less danger of the concrete spalling an e!posingthe reinforcement #eflection re."irements will generally govern slab thicknesswhich sho"ld not be less than &(* mm

    Typical ribbed and waffle slab are shown in 4ig"re 2&97c8$ 7d8: Ribbed slabs$which are two+way spanning and are constr"cted with ribs in both direction ofspan Ribbed slab floors are formed "sing temporary or permanent sh"tteringsystem while the hollow block floor is generally constr"cted with block made ofclay tile or with concrete containing a light+weight aggregate ;f the block ares"itably man"fact"red and have an ade."ate strength they can be considered tocontrib"te to the strength of the slab in the design calc"lations$ b"t in manydesigns no s"ch allowance is made

    The principal advantage of these floors is the red"ction in weight achieved byremoving part of the concrete below the ne"tral a!is and$ in the case of the hollowblock floor$ replacing it with a lighter form of constr"ction Ribbed and hollowblock floors are economical for b"ildings where there are long spans$ over abo"t *m$ and light or moderate live loads$ s"ch as in hospital wards or apartment

    b"ildings They wo"ld not be s"itable for str"ct"res having a heavy loading$ s"chas wareho"ses and garages

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    as they are stopped off$ there is no abr"pt change in cross+section e!tendingacross the slab The slabs are "s"ally made solid "nder partitions andconcentrated loads #"ring constr"ction the hollow tiles sho"ld be well soaked inwater prior to placing the concrete$ otherwise shrinkage cracking of the topconcrete flange is liable to occ"r


    -S /&&) permit the "se of simplified load arrangement for all slabs of ma!im"m"ltimate design load thro"gho"t all spans or panels provided that the followingcondition are met1

    a8 in one+way slab$ the area of each bay > 2) m(b8 ?ive load$ @k &(* #ead load$ Gkc8 ?ive load$ @k * k

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    C D







    Beam AC and BD

    w = n lx/ 3






    E F




    Beam AB and CD

    w = n lx/ 6 {3 !l

    x/ l



    #efine the type of slab either one+way direction or two+way direction$ fordetermine the shape of load distrib"tion from slab to beam

    ;fIy6IxF ( consider as two+way slab Iy6Ix > ( consider as one+way slab

    where Ix + length of shorter side Iy + length of longer side

    a8 ne+way slab

    b8 Two+way slab

    -eam A- and C#w = n lx/ "

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    4ig"re E3 ?oad distrib"tion of slabS#EAR IN SLAB

    The shear resistance of slab may be calc"lated by the proced"res given in -S/&&)$ Cl2**( I!perimental works has indicated that$ compared wit beams$

    shallow slab fail at slightly higher shear stresses and this is incorporated into theval"es of design "ltimate shear stress vc7Refer to Table 2$ -S /&&)8 The shearstress at a section in a solid slab is given by1

    v = Vb.d

    where Vis the shear force d"e to "ltimate load$ dis the effective depth of the slaband b is the width of section considered 7Refer to Table 2&D and Cl 2**(8Calc"lation is "s"ally based on strip of slab &m wide

    The -S /&&) re."ires that for solid slab1

    & vF )/ J fc"or *

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    e."al to at least don either sideCheck sho"ld also be "ndertaken to ens"re that the stress vcalc"lated forthe perimeter at the face of the loaded area is less than smaller of )/ J fc"or *

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    service stress of 2)D

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    The ma!im"m clear spacing given in Table 22)$ and Cla"se 2&(&&$ -S /&&)$7apply to bars in beams when a ma!im"m likely crack width of )2 mm isacceptable an the cover to reinforcement does not e!ceed *) mm8$ and are similarto beams e!cept that for thin slabs$ or if the tensile steel percentage is small$

    spacing may be increased from those given in Table 22)$ -S /&&) to a ma!im"mof the lesser of 2dor D*) mm

    c8 Reinforcement in the flange of a T P or ?+-eam5hen the slab from the flange of a T or ? beam the area of reinforcement in theflange and at right angles to the beam sho"ld not be less than )&* percent of thelongit"dinal cross+section of the flange

    d8 C"rtailment and anchorage of reinforcement

    At a simply s"pported end the bars sho"ld be anchored as specified in 4ig"re 2D

    4ig"re D3 Anchorage at simple s"pported for a slab

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    The slabs are design as if they consist of a series of beams of & m breadthThe main steel is in the direction of the span and secondary or distrib"tionsteel re."ired in the transverse direction The main steel sho"ld from theo"ter layer of reinforcement to give it the ma!im"m level arm

    The calc"lations for bending reinforcement follow a similar proced"re tothat "sed in beam design The lever+arm c"rve of 4ig"re 2/ is "sed todetermine the lever arm 7!8 and the area of tension reinforcement is thengiven by1

    As= "#/ 0.$% fy.!

    4or solid slabs spanning one way the simplified r"les for c"rtailing bars asshown in 4ig"re 2 may be "sed provided the loads are s"bstantially"niformly distrib"ted 5ith a contin"o"s slab it is also necessary that thespans are appro!imately e."al the simplified single load case analysis has

    been "sed


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