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top of the column if there are braces at point b and consideration is given to the compression in the flange when evaluating its stiffness. In general, a brace, such as a bottom chord extension from the joist, should be used at point a. Beam web stiffeners at the column location will also be effective unless bottom flange lateral buckling is critical.

Another common faulty bracing detail is shown in Figure 32.20. The girts that frame into the column flange prevent weak-axis translation at the braced flange. Since the girts are discontinuous, they will not prevent twist of the cross-section and will force the column to buckle about a restrained axis (see also Figure 32.9b). For this column, there are three possible buckling modes: strong-axis flexural buckling (Lb = KLC), weak-axis flexural buckling (Lb = KLG), and torsional buckling about a restrained axis (Lb = KLC, ybr = a assuming no twist at column ends).

Nomenclature

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