huangyhg

torsional analysis of a beam with web stiffeners
i am trying to analyse a wide flange section with web stiffners to verify that it will be able to accept a torsional load. the w14x30 currently has 1/4" plate each side at 48" o.c. aisc steel design guide 9 "torsional analysis of structural steel members" does not address this situation. does anyone know of a reference that does address situation? and/or software?
jimrcasper: i do not know how precise you wanted to be but sap2000 is a good software. in addition, you can divide your beam+stiffener in several sections (x section wise) to calculate geometric properties of the whole system, stresses, angle of twist, etc. any mechanics of material book can help you w/ the procedure..
1prsplmps1
i don't think you can account for the stiffeners with regular analysis. you would have to take all those equations and solve them with the condition that the cross section won't warp at the stiffener location but will warp everywhere else. that's why it isn't included in the design guide. even though you stiffen the section somewhat it really won't help that much. your other option is an intensive fea. stiffeners at 48" o.c. won't help much anyway. your flanges will still bend laterally regardless of stiffeners. just design it as in dg9.
stiffeners don't add anything to the torsional stiffness or to the torsional capacity of a wide flange. that is why there isn't anything in the aisc design guide.
actually stiffeners for steel wf lintels supporting eccentric siding loads had been used to increase the warp coefficient (@ the stiffeners location) and therefore to increase a bit the torsional capacity of the wf. asce have few journals on the subject..
corrected.....i should have said "stiffeners don't add much at all..."
usually when i run into a torsional situation, i try to get two
there's a book titled "design of welded structures" published by the james f. lincol arc welding foundation (cleveland, ohio) that deals with torsion.
basically, the principles in there are:
1. avoid torsion
2. if you can't avoid it, then use a closed shape (i.e. hss) with rigid end connections
in other words, w, c, s, l shapes etc are all lousy at resisting torsion. think of a paper towel tube with a cut along the length.
if all else fails, "stiffener plates" welded to the web on a 45 degree angle would help a little
jc
the book bonjoy refers to is excellent and i agree with his post. be sure to read the section about torsional rigidity, it is not the same as the sum of the moments of inertias,in fact the rigidity is much less. good examples are shown in the book. (it used to be really cheap to buy)
nz
bonjoy - good analogy to the paper tube. my mechanics prof used a different analogy to visualize relative torsional stiffnesses.
like these...

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