bjb
Structural
- Nov 8, 2002
- 455
The LRFD 3rd Edition says that cross frames or diaphragms can be a torsional braces, and gives equations for required strength and stiffness. If you have steel framing without a floor or roof diaphragm, can the infill beams be considered as torsional braces if you connect them to the girders by welding a full depth stiffener plate to the girder, and then attaching the infill beam with slip critical bolts designed for the required moment? This seems like it should work to brace the girder because twist of the section is prevented, and distortion of the girder web is also prevented.
I have known some engineers to believe that an infill beam with a double angle connection is enough to be considered as a torsional brace, but the LRFD commentary says that partially restrained connections can be used if their stiffness is considered in evaluating the torsional brace stiffness. Since double angle connections are intended to be flexible it seems to me that these connections are not acceptable for a torsional brace connection.
I have known some engineers to believe that an infill beam with a double angle connection is enough to be considered as a torsional brace, but the LRFD commentary says that partially restrained connections can be used if their stiffness is considered in evaluating the torsional brace stiffness. Since double angle connections are intended to be flexible it seems to me that these connections are not acceptable for a torsional brace connection.
