Torsional Force - Wide Flange Beam

[Veer007]

Hey guys, do you ever encounter the w-beam has torsional force? if so what's the condition for connecting the beam to column, i have seen the w-beam has either axial or moment force, and HSS beam has torsional force. Can anyone assist me!!

Thanks in advance!!

 

[Lomarandil]

It all depends on the design. What is causing the torsion, and how does that get carried out of the beam?

If you have perpendicular framing between the columns (like a floor system with pattern live load), then the torsion probably is mostly carried into that framing, and not into the columns. You can then usually design and detail the beam-column connections for a "torsionally pinned" condition, and use a simple connection (like a shear tab).

If the torsion is primarily carried through the columns (or other framing at the column line), then the connection needs to be "torsionally restrained" in order to pass that torsion force along. There are different ways to make that connection, but almost all of them will engage the beam flanges.

AISC design guide 9 (free to members) will have a lot of information about the design of the beam. I don't believe it talks much about the connection itself.





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just call me Lo.

 

[Veer007]

Thank you lo!! are you saying about beam framing? if there are beams interconnected with supporting beam between the column span, the beam doesn't have torsional force, otherwise it may have, am i right?

My question is w-beam ever have torsional force? i thought it doesn't, due to it's shape!!

Thanks in advance!!

 

[Veer007]

I have AISC 15th edition, can you please let me know where does this shows? about torsional force!!

Thanks in advance!!

 

[Lomarandil]

Even if there are framing beams between the column span, the main beam (most of the time) will carry an applied torsion as some internal torsional force. The beam needs to be designed for that (in the member selection/design). The details of the framing beams will dictate how the applied torsion is related to internal torsional force.

If there are framing beams between the column span, the connection between the main beam and columns might not need to carry torsion (as the torsion reaction can be provided by the framing beams instead, which are often more rigid anyway). In this case, the framing beams need to be designed and detailed to carry the torsional reaction.

If there are no framing beams (or composite slab, etc) and torsion is applied to the main beam, both the main beam and its connection to columns needs to be designed for torsion.

W-beams and other "open" cross section members are not as stiff as closed cross sections (like an HSS). However, if the structural system requires it for stability, they will still carry torsional forces. This is an analysis issue, not specific to AISC or steel.

Can you post a sketch showing your complete structural system? It would be better to address specifics.

----
just call me Lo.

 

[WARose]

Simple shear connections cannot transfer a (significant) torsional load. See this thread:

https://www.eng-tips.com/viewthread.cfm?qid=427598

You will need some sort of flange restraint (or intermediate members to take it out).

 

[calvinandhobbes10]

Intermediate kickers are preferable to resolve the torsion.

If not an option (stairwells), yes I use HSS designed for torsion or weak axis bending.

For W torsion connections, I would use one of the typical moment connections from AISC. Gives you a resisting force couple.

 

[TehMightyEngineer]

A trick I've used before on an existing monorail that we applied a large torsional load to was to box in the ends of the W section with plates at the flanges.

See attached.


Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[Veer007]

Thank you guys, provided info is most helpful!

Thanks in advance!!

 

[Tomfh]

Open sections are not very good torsion members. They can carry some torsion, but not a great deal. They have limited strength, and are not very stiff torsionally. Nothing like as stiff and strong as the same size box section.

 

[canwesteng]

Really depends on the magnitude of torsion. You can make clip angles work for small loads. You also need to distinguish between what AISC calls a torsional pin and torsional fixed support. Neither are free to rotate, but one will restraint pure torsion and the other will restrain warping torsion. Impossible to give any substantial advice without a sketch or some numbers though.