A steel beam is subjected to a concentrated load at mid-span. If the lateral-torsional buckling is a concern, which of the following modifications would most effectively increase the design moment capacity M_n without changing the section profile?

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Civil Engineering QUESTION #6603

Question 1

A steel beam is subjected to a concentrated load at mid-span. If the lateral-torsional buckling is a concern, which of the following modifications would most effectively increase the design moment capacity $M_n$ without changing the section profile?

Increasing the yield strength of the steel ($F_y$)
Providing lateral bracing at the mid-span✔️
Increasing the span length between supports
Decreasing the thickness of the web

Correct Answer Explanation

Lateral-torsional buckling (LTB) is heavily dependent on the unbraced length $L_b$. Providing lateral bracing at mid-span reduces $L_b$ by half, significantly increasing the moment capacity in the LTB-limited regime.

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