Lateral Bracing in ETABS

[meistersd]

When we are designing a steel structure in ETABS, I see that we can assign lateral bracing to the main beams supported by secondary beams. Should we always assign this property to the floor beams? What is the significance of assigning this lateral bracing? How can we be assured that the secondary beams provide enough lateral bracing and prevent lateral torsional buckling of those primary beams?

 

[271828]

I tried to use this feature a few years ago and gave up because it kept giving weird results. Thus, test it out on some easy cases to make sure you agree with its calcs. For a typical floor beam with positive moment and connection to the deck/slab, the unbraced length is typically zero so these checks might not apply.

The AISC Specification Appendix 6 provides equations for the required strength and stiffness of braces. I'd recommend checking it out. You might also find an old copy online of the Yuga and Helwig stability bracing seminars from a few years ago, probably about 2005.

 

[SteelStructureDesign]

If we would like to assign this property to the floor beams, should we do like below? (as an example)

1) ...\ Lateral Bracing \ Specify Uniform Bracing \ 0 to 1 : Top (Because the main beam is braced with deck and secondary beams on top) (I assume that secondary beams are much smaller than the main beam.)

2) ... \ Lateral Bracing \ Specify Point Bracing \ 0.5 : Bottom (I assume that the bottom flange is braced with another member (not secondary beams)in the middle)

Regards,