Allowable beam rotation
Allowable beam rotation
(OP)
Can anyone provide some guidance on allowable rotations of W-sections for servicability considerations?
I have an architecturally finished wall section being supported by the W-sections. However, the wall is two feet off the centerline of the beam, and is creating a substantial torsional moment. The wall finish is sensitive to deformation and the beams cannot be laterally braced.
Any guidance on this issue would be greatly appreciated.
I have an architecturally finished wall section being supported by the W-sections. However, the wall is two feet off the centerline of the beam, and is creating a substantial torsional moment. The wall finish is sensitive to deformation and the beams cannot be laterally braced.
Any guidance on this issue would be greatly appreciated.






RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation
But, back to your original question--the serviceability issue is with items ATTACHED to the beam, and not the beam itself. For example, what does the beam rotation do to the wall system? A small rotation in the beam could result in a large deflection in the wall system. The wall system will rotate with the beam, where it is attached to the beam.
DaveAtkins
RE: Allowable beam rotation
I have taken care of local deflections on the wall.
I was worried about the beam rotations because any differential in rotation from beam to beam could cause deformations. I had hoped to counteract this by limiting beam sizes, but I am limited with how large a beam I can use.
RE: Allowable beam rotation
RE: Allowable beam rotation
Anyhow with this limited understanding in mind I have two comments:
1. If you are concerned about the rotation of the beam then the beam probably doesnt work strength wise anyhow. Double check your numbers.
2. how are the beams restrained at the ends against torsion?
In this type of situation, I would usually weld an angle to the opposite side from the cantilever to take out the torsion from the cantilever. If the beam is not restrained against torsion at the ends then it will rotate a little to the point that there is negligible torsion in the beam and the full moment goes into the backspan.
Also be aware that this type of detail will amplify the effective load on the nearest beam.
As you have correctly realised, it is the deflection of the line of support directly under the wall that matters. Calculate the maximum allowable deflection at this point as if this line was a beam, then compare your actual deflection from combined cantilever, beam and rotation deflection to this number.
csd
RE: Allowable beam rotation
RE: Allowable beam rotation
Is this possible?
Mike McCann
McCann Engineering
RE: Allowable beam rotation
I would suggest something like Mr. McCann. Instead of a cantilever hanging off of one side of the beam, provide beams on the opposite side of the main support to turn the cantilever beams into overhangs. If you can't have those bear on the supporting wide flange, then frame them into the wide flange each side and provide a continuous splice connection.
RE: Allowable beam rotation
Very little.
I think they have very little stiffness....
(hint hint) Do what these excellent posters say above and use an HSS. If your wall is brittle as you say, you'll regret using a WF.
RE: Allowable beam rotation
We obtained allowable local deflections from the architect and from there determined allowable rotations of the W-shape.
W-shapes were used because the owner wished that the new additional structural system (which would be partially exposed) match the existing system (W-shapes).
We had beam to column moment connections, but were still getting minor (<2degree) rotations at mid-span which were still above the allowable rotation determined above. This was counter-acted by selecting the appropriate (if slightly larger) shape and adding stiffeners at quarterpoints along the beam.
RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation
RE: Allowable beam rotation