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A hall in a building has a floor consisting of a One way slab Continous slab cast with simply supported beams of width 250mm spaced at 4m c/c (fig3).

The clear span of beam is 9m. Assuming live load=3kN/m2, partition load 1kN/m2 and load due to finishes 0.6 kN/m2.

Design the slab with Grade of concrete is M20 and steel is Fe 415. Use LSM method. Draw neat reinforcement diagram.

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Solution:

ly=9m

lx=4m

lylx=94=2.25>2

One way continuous slab

Given:

Live load = 3KN/m2

Partition load = 1KN/m2

F.F = 0.6KN/m2

M20 Fe415

beam = 250 mm

brick wall = 230 mm

1] Calculation of depth

dreq=lxld×MF=400026×1.4=109.89120mmD=120+20+102=145mm


2] Load calculation

i) Dead load

a) s/w of slab =25×D=25×0.145=3.625KN/m2Partition load=1KN/m2Floor finish=0.6KN/m2----------------5.225KN/m2WuDL=1.5×5.225=7.84KN/m

ii) Live load

LL=3KN/m2

WULL=4.5KN/m2

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D.L+112116116112

L.L+1101911219

Mu1=112×7.84×42+110×4.5×42=17.65KNmMuB=110×7.84×4219×4.5×42=20.54KNmMu2=116×7.84×42+112×4.5×42=13.84KNmMuc=112×7.84×42+(19)×4.5×42=18.45KNm


4] Check for depth

mmmax=Rumax bd2d=20.54×1000.138×20×1000d=86.26mm<120mmSafe in depth


5] Calculation of steel

a) Main steel

1) Ast1=0.5×20×1000×120415[1146×176.5×10620×1000×1202]=441.24mm2Astmin=174mm2Use commϕSpacing=π/4×102441.24×1000=177.99mm150mmUse 10mm ϕ @ 150 mm

2) AstB=521.30mm2

Provide 10mm ϕ 125 mm c/c

3) Ast2=339.53mm2

Provide 10mm ϕ @ 200 mm c/c

4) Astc=463.14mm2

Provide 10mm ϕ @ 150 mm c/c

b) Distribution steel

Astmin=174mm2

Provide 8 mm ϕ @ 275 mm c/c

Astp=π/4×102150×1000=523.6mm2


6] Check for deflection Page no 38 IS456

Fs=0.58×415×441.2953.6=202.83N/mm224N/mm2Pt%=523.61000×120×100=0.436%MF=1.3d=400026×1.3=118.34mm<120mmSafe in deflection


7] Check for shear

At B

VuB=αDL×WUD×lx+αuWULL×lx=0.6×7.84×4+0.6×7.84×4=37.63KNVuD=VuB=37.63KNVuc=k τUC bdk=1.3 (for d150)Pt%=Astbd×100=521.301000×120×100=0.430.250.360.4310.500.48τuc=0.4120N/mm2Vuc=k τuc bd=1.3×0.421×1000×120=65.67KN>VUD=37.63KNSafe in shear


8] Check for development length

Ld=0.87fyϕ4τbd=0.87×415×104×1.2×1.6=470.11mmM1=17.652=8.825KNVA=21.9KNlo=12ϕ or d=120mm=644.03mmLd<13M1V+ls

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