Torsional analysis

[kindarc]

A w8x40 steel beam with a continuous 3/8" x 14" wide steel plate welded to the top flange, spanning 25.33', fixed at both ends into a masonry wall, with precast concrete roof planks bearing 8" from the beam center onto the steel top plate with a unifrom total dead and live load producing 920 PLF. Can this beam resist the torsion created by this eccentric load? What formula is needed to check this condition?

 

[frv]

Look at AISC DG 9.

 

[JoshPlumSE]

I believe there are a number of existing threads which discuss this topic. Not really sure of the proper way to reference another thread, but I'll give it a shot.

http://www.eng-tips.com/viewthread.cfm?qid=243419

 

[hokie66]

If the bearing is 8" from the beam center, and the plate is 14" wide, isn't the bearing outside the plate?

 

[JLNJ]

My answer is "maybe". As in you may be hiring a structural engineer.

The greater the torsion the greater the fixity required at the masonry wall. The beam-to-wall connection will need a good look.

 

[JAE]

Wide flanges have very little torsional stiffness so the chance that the beam will rotate to an unstable condition is high.

 

[hokie66]

A picture would help. Based on the original post, I don't believe we know that the beam is actually torsionally loaded. But if the end of the plank is 8" from the center of the beam, no need to compute...it won't work.

 

[steellion]

It almost certainly won't work for torsion for the condition you described, but an easy way to solve this is the brace the beam against torsion so that it cannot rotate. Angle kickers from the bottom flange of the spandrel beam to the top flange of the adjacent beam work nicely. Spacing is determined by the equations in AISC DG9.