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Ø12 @4.00in c/c
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Ø12 @8.00in c/c
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Ø10 @9.00in c/c
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Ø12 @4.00in c/c
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Ø10 @10.00in c/c
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Design Data
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Riser, R =6in
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Trade, T =10in
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f'c =3,000psi
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fy =60,000psi
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Effective Span Length
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L1 = 3.50ft
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Horizontal Span, L =L1+L2+L3L2 = 7.50ft
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=15.00ftL3 = 4.00ft
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Thickness of Waist Slab
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Thickness, t =Span / 20
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=9.00in
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Say, t =7.00in
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So, d =6.00in
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Loads on Slab
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(1)
D.L. of Slab on slope with landing slab =
(t/12)x150psf
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=87.50psf
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(2)
D.L. due to Riser =
Load on slope x (R2+T2) / T2
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=102.04psf
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(3)L.L. = 100.00psf
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(4)F.F. =30.00psf
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Total D.L.=219.54psf
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Total L.L.=100.00psf
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Ultimate Load, w =
1.4 D.L. + 1.7 L.L.
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=477.36psf
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Moment
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Moment for Simply Supported Span, Mu =
w*L2/8
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=13,425.70lb-ft/ft
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=161,108.43lb-in/ft
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Checking Thickness
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P =0.75 Pb =
0.75x0.85x0.85x(f'c/fy)x(87000/(87000+fy))
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=0.016
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Mu =
ØPfybd2(1-0.59P(fy/f'c)
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d =4.373in
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t =5.373in <7.00in, So, OK
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So, t =7.00in
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and d =6.00in
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Main Reinfrocement
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As =
Mu / ((Øfy(d-a/2))
Let, a=1in
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=0.542in2 / ft
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Check,a=
Asfy / 0.85f'cb
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=1.064in =1in, So OK
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pmin =200 / fy =0.003
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Asmin =
pmin*b*d =
0.240in2
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So, As =0.542in2 / ft
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Spacing, S = 0.2*12/As
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=4.42inso, Ø12 @4.00in c/c
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Distribution Reinforcement (Temp & Shrin. Reinforcement)
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Distribution Rod =
0.15% of the Cross-sectonal area
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=0.13in2/ ft