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Re: Torsion on a steel tube and AISC WINTORQ program

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>I have a question regarding calculating the shear stress in a steel tube.  
>I have the Steel Design Guide Torsional Analysis of Structural Steel 
>Members and the WINTORQ program from AISC.  
This happens a lot with design codes. What you're seeing is the effects 
of various simplifications and rephrasing of the original torsional 
stress relationships developed from basic mechanics. 

You weren't too clear about what you needed to know, but you can clear up 
this sort of thing by making sure you understand the basic theory, which 
for thin walled tubular sections isn't too tough--it's in Timoshenko's 
strength of materials book and very well presented. Once you understand 
the basic relationships and methodology (probably the membrane analogy in 
this case), you can sort out the differences and identify what made the 
differences between the various answers. Between one reference using the 
actual shear modulus, G, and a second using E with the conversion buried 
in a bugger factor and a third assuming steel and not showing the modulus 
explicitly, things that appear different turn out to be very similar.

If you're not sure about a computer program, the only real way is to give 
it a couple of problems whose answer you know and see if you can dope out 
the methodology by going through the output listing a line at a time.

I've had to go through this with some pressure vessel code rules and at 
one point with the thin-walled stability relationships for steel beam 
sections. It takes some study and some time, but once you've done it the 
rules make a lot more sense. Sounds like you've actually started an 
exercise of the sort, anyway. 

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw(--nospam--at)        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)

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