Angle of twist - Torsion
Angle of twist - Torsion
(OP)
I have a Channel section and I am trying to check it for torsion. It is simply supported.
I noticed the spread sheets out there calculate the angle of twist but dont know this number has to be check about what number? Where can I find allowable angle of twist?
If is not needed then why these spread sheets calculate it?
If more infor is need please ask and I will provide
Thanks
I noticed the spread sheets out there calculate the angle of twist but dont know this number has to be check about what number? Where can I find allowable angle of twist?
If is not needed then why these spread sheets calculate it?
If more infor is need please ask and I will provide
Thanks






RE: Angle of twist - Torsion
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Angle of twist - Torsion
May I ask this angle of twist we measure for a channel section is about the ceneter of gravity or it is amount of twist about shear center?
RE: Angle of twist - Torsion
Jim
RE: Angle of twist - Torsion
can you close the channel with a over plate (and make a tube out of it) ?
consider deflection ... the allowable deflection is based on how springy the people in the building will perceive it to be. torsional deflection is bounded by the same limits ... what is perceptible ? what messes with the operation of your installation ?
another day in paradise, or is paradise one day closer ?
RE: Angle of twist - Torsion
Also, it makes no difference about which point you measure the angle of twist. It is the amount the cross section has rotated from its original position and has nothing to do with center of gravity, shear center or any other point on the cross section.
BA
RE: Angle of twist - Torsion
RE: Angle of twist - Torsion
The best way to check a channel for torsion is to redistribute the loads so that the torsion on the channel = 0 < the torsion allowed on the channel.
When dealing with torsion, this typically means that the pinned connection can take the twisting motion but is allowing the channel flanges to warp (top flange rotates opposite direction from the bottom flange). Verify that the shear plate, or whatever is providing your connection, can take the torsion reaction.
If you can't deal with torsion on a channel the proper way (see above), then you will need to do a stress check on your section for the added normal stresses due to warping and shear stresses due to pure torsion. Sharpen your pencil and get your difEQ book out because the distribution of pure torsion to warping is fairly involved. Of course, you could grab a copy of AISC Steel Design Guide 9 and match up your conditions with one of the lookup charts in the back. I would recommend that you not use an excel spreadsheet unless you develop it yourself.
As for allowable twist, if this a serviceability condition, don't use a channel. I calculate twist on my torsion members as part of the process of getting to my pure torsion stresses.