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Example 1: nominal moment for rectangular beam with two layer of reinforcing steel

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determine the nominal or theoretical moment capacity Mn for beam in figure 1 if fy= 60,000 psi and fc'= 4000 psi.
Figure 1







Figure 2




Mn=As*fy((d-a/2))

085*fc'*a*b=As*fy

a=(As*fy)/(0.85*fc'*b)
a=(6*60,000)/(0.85*4000*16)
a=6.62in

Mn=6*60,000*(26.25-6.62/2)
Mn=85258400lb-in=688.20 k-ft

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