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Fw: Torsion on a steel tube and AISC WINTORQ program

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>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.
 
Let me try to clear up my question:  I understand how 1,2 and 3 are derived for thin wall tube sections.   I also understand how to derive 5 for maximum shear stress on a solid circular section.  
Why is the program giving an output of "wall shear stress value", for a thin wall tube, consistent with 5, instead of 1,2 and 3?  (The (theta') provided by the program, when used in equation 4, gives a shear stress that matches shear stress given from equation 5.)   The program appears to give an incorrect value for shear stress, unless I am missing something. 
 
>have you contacted AISC yet?  My experience is that they're pretty responsive to questions like >that.  Don't know much about that program, sounds good, come across any negatives yet? (besides >the issue mentioned below)
 
I will try and contact AISC and let you know what I find out.  The WINTORQ program is an excellent design aid for torsion on wide flange members although it could be a bit more "output friendly".  It took me awhile, with the help of the Design Guide,  to figure out how to use the values it was providing.  The program gives all the values you would otherwise have to get by interpolating charts provided in the Design Guide.  It still takes another (easy) step to calculate rotation, shear stress and normal stress by hand.  For $30, it was a great investment!  :-)  
 
Thank you for the responses thus far!
 
Jesse Gobeli, P.E.
Dublin, OH 
 
----- Original Message -----
Sent: Tuesday, March 18, 2003 9:01 AM
Subject: Torsion on a steel tube and AISC WINTORQ program

List,
 
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. 
 
Typically, I would calculate the shear stress in a tube using the formula: 
1.  shear stress = T / (2*b^2*t) (from table 4.1 of the Design Guide)
2.  shear stress = T / (2*t*Ao)  for constant T (Design Guide Eq. 4.4)  (This is the method used in example 5.2 of the Design Guide).
3.  shear stress = T / C (from Hollow Structural Sections Connection Manual spec. eq. 6-1, C is tabulated for each shape).
 
Methods 1,2 and 3 seem to give the same result. 
 
The WINTORQ program gives a "wall shear stress" value which seems to come from the following equation: 
4.  shear stress = G*t*theta'   (Design Guide Eq. 4.1)  (theta' from WINTORQ program)
This result can also be obtained using: 
5.  shear stress = T*t/J 
 
The problem is, the results from 1,2 and 3 are somewhat higher than the values from 4 and 5.  Since the Design Guide shows an example based on 2, but the WINTORQ program provides a value based on 4, I am not sure which value to use.  WINTORQ does not give any of the stresses obtained by 1,2 and 3.
 
(By the way, I have worked through the examples in the design guide for Wide Flanges, and along with the  WINTORQ program, they have been a HUGE help in understanding torsion on a wide flange beam.)
 
Jesse Gobeli, P.E.
Dublin, OH