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Moment Capacity Near Point of Lateral Bracing

Moment Capacity Near Point of Lateral Bracing

Moment Capacity Near Point of Lateral Bracing

(OP)
Hello, I have a question that I cannot find the correct answer to online and which has stumped one of my coworkers.
I have a beam approx. 45' long, pinned on the ends with a column about 32' from one end (so a continuous span). After applying the loads the greatest negative moment occurs at the column. The moment is negative for about another 13' from the column in the 32' span. When I calculate my moment capacity it is greatly reduced because I have a 32' span when the compression flange (bottom of beam) is unbraced. Cb=1.4 which helps slightly but according to code that beam will fail due to LTB 1 unit away from the column. I can't imagine that beam would buckle so close to the point of lateral support.

anyone else run into this before?

Thank you,

Steve H. E.I.T.

RE: Moment Capacity Near Point of Lateral Bracing

Quote (OP)

according to code that beam will fail due to LTB 1 unit away from the column

LTB will occur over the entire 32' unbraced length of beam. It isn't a phenomenon that occurs just at a discrete point. If LTB occurs, your maximum bottom flange lateral displacement will still probably occur in the middle third of that 32' span.

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