Reinforced Concrete Beam Design Example

Statement

A single reinforced rectangular beam has a width of 11” and effective depth of 18”. If f’c = 3ksi and fy is 40ksi. Calculate the moment capacity M_n, if A_s = 5in²

Given

1. Width of beam = b = 11”
2. Effective depth of reinforced concrete beam = d = 18”
3. f’c = 3 Ksi
4. Fy = 40 ksi
5. A_s = 5in²

Required

Moment capacity of the reinforced concrete beam = ?

Solution

Given problem is the analysis case. For understanding the solution, one must should have ACI 318M-08 building code.

find steel ratio by using formula defined by ACI 318M-08

Ρ = AS/bd = 5/(11*18) =  0.025

Now find respective value of “R”  from Graph A.1a (Moment capacity of Rectangular beam)

Steel ratio vs R graph (Design Aids)

R = 800 Psi

Mn =2851.2 K-in.