Torsion on beams from Eccentric Connections 1

[eccentric]

Hello all,

I am looking for a simple method of determining if stiffeners and/or diagonal bracing is needed for a composite beam that is supporting an eccentric load. The eccentric load my be from a hanger, a cladding connection, or similar. AISC Design Guide 9 is OK for non-composite members but doesn't really address this situation.

In short, I believe that the diagonal brace is often not needed if stiffeners are used because the stiffeners transfer the moment into the slab (though this may not be ok either).

I couldn't find anything at AISC's website and am glad that I have found this forum.

Thanks in advance for any information you can share, keep your stress low

 

[dlew]

eccentric,

I assume the diagonal bracing you mentioned is a member from the bottom flange of the eccentrically beam to the top flange of the next parallel beam.

In my opinion, such diagonal bracing is very effective and clean. Vertical stiffeners will brace the bottom flange, but do not eliminate the torsion in the beam. Also, if the beam is composite, a portion of the torsion will be carried by the slab. The torsion stresses in the beam and the slab should be investigated in this case.

AEF

 

[eccentric]

Thanks AEF,

I agree that bracing is generally simple and very effective. My question arises because occasionally I have been unable to get the bracing in or the loads have been fairly small and I didn't want to use bracing if it isn't needed.

As a follow on question, has anyone seen any literature discussing the torsion distribution between beam and slab for a composite beam? I would speculate that using stiffeners near the loading point would transfer most of the torsional loading into the slab (by restraining the warping of the section).

 

[JAE]

I would normally not count on this transfer of moment into your slab because your shear studs were not designed to take both the horizontal shear AND the stud tension induced by the beam twisting. (I see the studs acting in tension and one flange acting in compression on the concrete slab.

Also - your slab would have to be checked for the bending that would result, and slabs aren't that stiff. If your exterior veneer is brick, be careful that you combine the vertical deflection of your beam with the torsional movement of the beam to get a combined effect - brick usually needs L/600 limit on deflection.