Torsional analysis of a beam with web stiffeners
Torsional analysis of a beam with web stiffeners
(OP)
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?






RE: Torsional analysis of a beam with web stiffeners
1prsplmps1
RE: Torsional analysis of a beam with web stiffeners
RE: Torsional analysis of a beam with web stiffeners
RE: Torsional analysis of a beam with web stiffeners
RE: Torsional analysis of a beam with web stiffeners
RE: Torsional analysis of a beam with web stiffeners
Usually when I run into a torsional situation, I try to get two members resisting the load.
It becomes a simple exercise with vertical loads acting upon two separate beams.
Another solution is to weld a continuous plate up against the toes of the flanges thereby adding a second web parallel to the first. Then the torsion can be developed similarly to a HSS section.
Regards,
JPJ
RE: Torsional analysis of a beam with web stiffeners
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
RE: Torsional analysis of a beam with web stiffeners
NZ
RE: Torsional analysis of a beam with web stiffeners
If you look at the cross section of the member and visualize it as a cut opening in a flat sheet of plastic, then dip the flat sheet into a tub of soap, then induce a little air pressure on one side of the sheet, you will get a slightly bulging soap bubble.
The volume under the soap bubble is a measure of the relative torsional stiffness. So a pure pipe would have a circular cut-out in the sheet that leaves a full hole equal to the outside dia. of the pipe. The soap bubble would be large. If you cut a slit in the pipe lengthwise, you would only have a circular cut representing the 359 degrees of pipe wallFor a wide flange, you only have small little bulges along the individual plates and the volume is small.
RE: Torsional analysis of a beam with web stiffeners
RE: Torsional analysis of a beam with web stiffeners
Section 2.10 "Designing for Torsional Loading" covers the torsional subject extensively.
It is available from the Lincoln Arc Welding Foundation at give-it-away-for-almost-nothing prices. The cost is something like $5.00 for a printing cost and a small additional shipping cost.
It has something like 600 pages of heavy duty stuctural design concepts with examples shown.
Highly recommended for evey engineering library.
It even mentions the membrane concept JAE is talking about.
Regards to All,
JPJ
RE: Torsional analysis of a beam with web stiffeners
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RE: Torsional analysis of a beam with web stiffeners
The theory that you were discribing in the soap bubble analogy is refered to as Prandtl's Membrane Analogy, lots of fun.
Regards,
AUCE98
RE: Torsional analysis of a beam with web stiffeners
RE: Torsional analysis of a beam with web stiffeners
In this instance is "b" the height of the memeber(14"), the diagonal lenght of the member(19") or the width of the member (6.75")? I understood it to be the last case.
The book also refers to the torsional rigidity as being 3.54I, what is the "I" in this stiuation? The plates are at 45 degrees so there is no bending, just tension or compression. Thank you in advance for all your assistance.
RE: Torsional analysis of a beam with web stiffeners