Determining if a beam connection will torsionally brace a steel column?
Determining if a beam connection will torsionally brace a steel column?
(OP)
I sat in on an AISC seminar recently and recall the presenter discussing that a steel column needs to be "torsionally" restrained at any brace point to preclude any torsional buckling modes. So, I got to thinking about typical practices.
We often assume that steel beams framing into a column in each direction adequately brace the column for purposes of compression design. The beams, if adequately connected to the LFRS, certainly provide lateral bracing, but what about torsional bracing? Wouldn't this depend on what type of beam to column connection is provided? What about single plate shear connections? Does AISC provide any guidance on this matter?
Thanks.
We often assume that steel beams framing into a column in each direction adequately brace the column for purposes of compression design. The beams, if adequately connected to the LFRS, certainly provide lateral bracing, but what about torsional bracing? Wouldn't this depend on what type of beam to column connection is provided? What about single plate shear connections? Does AISC provide any guidance on this matter?
Thanks.






RE: Determining if a beam connection will torsionally brace a steel column?
Bracing systems that are attached only near the centroid of the member are generally ineffective in controlling twist.
RE: Determining if a beam connection will torsionally brace a steel column?
RE: Determining if a beam connection will torsionally brace a steel column?
I'm looking at the same section in AISC 360-05. I see requirements for axial stiffness of braces for restricting translation, but I do not see rotational stiffness requirements for preventing twist.
He worked an example where he checked the capacity of a 20' long W14x38 column that was braced at each end laterally and torsionally, and also braced at mid-span in the weak-axis laterally, but not torsionally. He checked three buckling failures based on three effective lengths:
KLx = 20' (strong-axis flexural buckling using Section E3)
KLy = 10' (weak-axis flexural buckling using Section E3)
KLz = 20' (torisional or flexural-torsional buckling using section E4)
RE: Determining if a beam connection will torsionally brace a steel column?
BA
RE: Determining if a beam connection will torsionally brace a steel column?
RE: Determining if a beam connection will torsionally brace a steel column?
However, he said there is some question as to whether or not extended end plate connections or connections involving deeply coped members are adequate as torsional bracing and that research is currently being conducted associated with this issue.