Top Flange Brace - Edge Beam 1

[ltfdrsn]

Hi,

I am designing a steel edge beam 28ft long, which will only take 2' of trib. load. There will be a concrete on metel deck placed on top of it. I was planning to design the wide flange beam as fully braced on the top. I was just wondering if there is an objection to that or not.

Thank you,

 

[BridgeSmith]

It depends on if the beam is connected to the metal deck adequately and rigidly enough to prevent lateral torsional buckling (LTB) of the flange. It doesn't take a strong connection, but it must prevent movement of the flange and must remain intact. Once there is eccentricity of the compression flange, the lateral forces can become large rather quickly.

We see this type of system often on bridge girders, where they provide small welds between a girder flange and the corrugated metal deck. After a few years the welds start cracking and we have to reduce the girder capacity significantly because compression flange can no longer be considered continuously braced.

 

[ahypek]

Yura has a lot of research available for lateral torsional buckling.

Engineering judgment is key here but the existence of a concrete slab above the beam will significantly inhibit lateral translation or rotation, especially under ultimate loading.

 

[JAE]

If you are using typical deck-to-beam connections (spot welds, power driven fasteners, screws) then you most likely have adequate bracing of your beam.
It doesn't take much lateral capacity to brace it. And if you lose connections from rust (inside a building probably not) then you've got bigger problems than LTB of the beam.



Check out Eng-Tips Forum's Policies here:
faq731-376