Bracing of a torsionally loaded WF beam
Bracing of a torsionally loaded WF beam
(OP)
We have a question going around the office..if a wide flange beam is braced on the compression flange (in this case the top flange) by bar joists, but an upper structure (raised aisle) is also attached to the beam at about midspan that will impart a torsional moment, will a web stiffener below the upper structure where the torsional moment is applied be enough to consider the beam braced against rotation when the upper structure is laterally loaded (wind)? Thanks for any help!






RE: Bracing of a torsionally loaded WF beam
RE: Bracing of a torsionally loaded WF beam
RE: Bracing of a torsionally loaded WF beam
RE: Bracing of a torsionally loaded WF beam
RE: Bracing of a torsionally loaded WF beam
RE: Bracing of a torsionally loaded WF beam
I agree with Ron, add some kickers to brace the bottom flange. If kickers are not possible, consider a closed shape. If a closed shape is not possible, check torsion on the I-beam per AISC Design Guide #9. The full procedure can be fairly complicated in my opinion.
As a simplification, (depending on your condition, span, end restraints etc) sometimes it is ok resolve the torsion force into a tension-compression couple taken out by the top and bottom flanges. You can then check the flanges alone for the weak axis bending of the flange spanning between points of torsional restraint. This is a simplification and can be easier than calculating the warping torsion equations etc.
RE: Bracing of a torsionally loaded WF beam
RE: Bracing of a torsionally loaded WF beam
If that is true, then the only way a stiffener does anything is if the connection between the bar joist and WF is adequate to transfer the moment (it won't be). This would be similar to trying to brace the bottom flange of a WF with a stiffener and studs into a slab - it works with studs, not just a puddle weld to the deck.
A kicker is the best option here.
RE: Bracing of a torsionally loaded WF beam
What checks need to be done?
I have a similar application right now
RE: Bracing of a torsionally loaded WF beam
RE: Bracing of a torsionally loaded WF beam
RE: Bracing of a torsionally loaded WF beam
TJ...using the kickers(best option), as suggested, to the bottom fla would change the end conditions of the bar joist from simple to fixed and impart an applied mom from the wind.
The WF would still rotate under wind load but would be self- limiting and only as much as the bar joists deflect...
if there is only one kicker(one side only), the WF would rotate
under dead and live on the bar joists, again, self-limiting..