3. For a continuous one-way slab, the maximum negative moment at support is dete

Question

3. For a continuous one-way slab, the maximum negative moment at support is determined to be 3.3 kip-ft/ft. Assume the slab thickness to he.6.in. size to he 1.3, Given f 5000 psi, normal weight concrete, -60000 ps and the bar i) Determine the ii) Also check the ACI Code requirements for minimum ii) Determine the required bar spacing to be provided in the transverse required reinforcement size and spacing to satisty AC Code flexural strength requirements slabs direction to satisfy ACI Code 7.12.2 requirements for minimum shrinkage Provide a neat sketch of the final design of the slab section. reinforcement in iv)

Explanation / Answer

i) Given moment in slab=3.3 kip-ft/ft = 39600 lb-in/ft

Width of slab=12"

Let area of steel required be Ast and depth of compression zone be a

0.85*12*5000*a=60000*Ast

a=1.176Ast

Assuming effective cover of 1", effective depth of slab=6-1=5in

lever arm = 5-a/2=5-0.588Ast

0.75*60000*Ast*(5-0.588a) = 39600

225000Ast-26460Ast2=39600

Ast = 0.18 in2

Area of steel needed = 0.18in2 /ft

Provide 2-#3 rebar per ft width. Therefore, provide #3@6" spacing.Steel provided=0.11*2=0.22 in2/ft

ii)Minimum area of steel per ACI = 3*sqrt(5000)*12*5/60000=0.21 in2/ft

Also, it should not ber less than 200*12*5/60000=0.2 in2/ft

The steel provided is greater than minimum steel

iii)Spacing required per Cl 7.12.2 for minimum shrinkage and temperature = 5*6=30 or 18" (whichever is less)

Therefore ,18 " spacing is needed

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