Determine the moment capacity of an ASTM 992 W18 × 40 floor beam with Fy = 50 ksi. Assume that the beam is fully braced laterally along the compression flange (see Figure 8.47) with a composite concrete deck securely anchored with shear studs.

Question

Determine the moment capacity of an ASTM 992 W18 × 40 floor beam with [latex]F_{ y }[/latex] = 50 ksi. Assume that the beam is fully braced laterally along the compression flange (see Figure 8.47) with a composite concrete deck securely anchored with shear studs.

Accepted Answer

A check must first be made to verify its compactness. For the W18 × 40,

[latex]d=17.90^{\prime \prime} ; b_{ f }=6.015^{\prime \prime} ; t_{ f }=0.525[/latex]

[latex]t_{ w }=0.315 ; h=15.5^{\prime \prime} ; Z _{ x }=78.4 in .^{4}[/latex]

[latex]\frac{b_{ f }}{2 t_{ f }}=\frac{6.015^{\prime \prime}}{2 imes 0.525^{\prime \prime}}=5.73 \leq 9.19 [/latex] for 50 ksi steel

and

[latex]\frac{h_{ c }}{t_{ w }}=\frac{15.50^{\prime \prime}}{0.315}=49.2 \leq 90.5[/latex]

The W18 × 40 section is compact, and the moment capacity will be equal to the plastic moment.

[latex]M_{ n }=M_{ p }=F_{ y } Z_{ x }=\left(50 k / in .^{2} ight)\left(78.4 in .^{4} ight)=3,920 k ext { -in. }[/latex]

[latex]M_{ n }[/latex]=3,920/12 = 327 k-ft.

Question 8.22: Determine the moment capacity of an ASTM 992 W18 × 40 floor ...

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