Torsion in Steel Edge Beam

[O_O]

Hi, With RC slab on top of Steel edge beam, is torsion a concern for the steel beam and why? I am going to use shear studs but am wondering if the connection will attract torsion in steel beam?

 

[hokie66]

As long as the slab is stiff enough to cope with rotation, torsion in the steel beam should not be a concern. This is called compatibility torsion. The type torsion which we mostly concern ourselves with is equilibrium torsion, such as you would have if the concrete slab is a cantilever without backspan.

 

[O_O]

Thanks for the quick reply hokie. I am not worried about the slab but the steel. I know with RC edge beam, the edge beam will crack under torsion and thus release the end moment but will the moment(torsion) be released here and how? My concern is what if the moment cannot be released and the beam fail due to the torsion? thanks

 

[hokie66]

A steel beam, and I imagine you are talking about a wide flange beam, is very flexible in torsion, so will just rotate a bit. Not an issue.

 

[CivilSigma]

I think if you are using shear studs to connect the beam to the concrete, then the lateral torsional stability of the beam will not be a problem.

The concrete slab would be providing the lateral bracing for the beam (otherwise if the beam is to fail in lateral torsional buckling, it would have to be loaded large enough to actually detach the concrete diaphragm system).

@hokie66 I believe that even the slightest torsion on a wide flange steel beam can cause it to yield. LTB is one of the most serious problems to design for.

 

[WARose]

Hi, With RC slab on top of Steel edge beam, is torsion a concern for the steel beam and why? I am going to use shear studs but am wondering if the connection will attract torsion in steel beam?

It's never been a consideration in any elevated slab I've done. (Never been a issue either.)

And I'm somebody who is paranoid about torsion.

 

[r13]

hokie is correct, without rigid connection in between, the beam might feel torsion caused by deformation compatibility, which is very difficult to evaluate. That's why you shall always design the edge beam for gravity load with a small eccentricity. The slab, though causes the torsion at first place, it essentially end up preventing the beam from roll over (to side way), so LTB will never be a concern, unless the beam is too weak to start with.

 

[haynewp]

I've never considered torsion for a steel edge beam nor for a steel edge girder. I don't think I have ever seen it considered in any designs I have reviewed either. This is from AISC's design guide on blast resistant buildings which says it's not usually considered for conventional designs. The slab rotations and deflections of a slab under blast is a much different case.

"Studies have concluded that when a steelframed structure is subjected to the shock of an
air blast, or to severe localized impact, the
following can occur:

• Twisting of beams—caused by lateral
fixity of the beam’s top flange created
by direct attachment to the in-plane
stiffness of the connecting floor
diaphragm (assuming the floor
diaphragm remains connected to beam
flange), accompanied by lateral bending
of those same beams framing into a
common column. Such load phenomena
are not typically accounted for in the
design of a beam and its beam-to
column connections, and will enable
gravity forces acting on contiguous floor
systems to have an adverse effect on
their supporting twisted beams and
connections."

 

[university_professor]

consider only direct torsional, not indirect.