Lateral support for a beam
Lateral support for a beam
(OP)
I told my boss that a W beam (if under loading and bending about weak axis)needs to be separately lateraly braced and being braced for bending about strong axis does not assure the bracing for bending about weak axis. May I ask if you think I am right.
We are talking about two parallel beams in air . No floor on them. Please see attachment.
Thank you
We are talking about two parallel beams in air . No floor on them. Please see attachment.
Thank you






RE: Lateral support for a beam
You will be worried about lateral torsional buckling for the strong axis, and if this is just a two beam system, you may have to consider global LTB for the two beam system, along with individual LTB. See attached paper for some discussion.
RE: Lateral support for a beam
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RE: Lateral support for a beam
@OP: It’s true, beams don’t laterally torsionally buckle when bent about their weak axes. Someone should explain why that is, of course, so that you can debate it with your supervisor. Everything in nature tends towards a state that minimizes potential energy. Unchecked, nature would very much like to roll our I-beams over weak axis so that deflection would increase, the loads would move closer to the earth, and potential energy would be minimized. Lateral torsional buckling of beams loaded strong axes reflects precisely this tendency. By the same token, it would make no sense for a beam loaded weak axis to roll over to the strong axis position as that would increase potential energy. Thus, no weak axis LTB. It would be much like hopping on a skateboard and having it coast uphill.
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RE: Lateral support for a beam
You are saying there is no need for bracing for bending about weak axis for lateral torsional buckling?
Did I understand it right?
I appreciate it simple language :)
Sincerely,
RE: Lateral support for a beam
RE: Lateral support for a beam
I appreciate for your valuable comments.
Have a good weekend
RE: Lateral support for a beam
It's worth noting that weak axis bracing IS sometimes required for axially loaded beams and columns if they need it. But this is to get the KL/r_y value up, not for lateral-torsional buckling.
Maine EIT, Civil/Structural.
RE: Lateral support for a beam
The answer is no, not for lateral torsional buckling. But if a force is applied at the arrow marked '2', the left beam will resist all of the force and the right beam will resist none of it. If the force is applied eccentrically, the left hand beam will rotate.
So the conclusion is that the bracing ensures that the two beams deflect equally at the brace point and prevents rotation of either beam, a simple form of load sharing.
BA