Warping Constant

[Bagman2524]

Can anyone explain what the warping constant Cw is and how it is calculated?

 

[JStephen]

This is discussed in Roark's Formulas for Stress and Strain- Section 9.3 in the 5th Edition. It also includes formulas for the Cw and for K (which appears to be J in the AISC books). It may take some juggling around with the fillet radius to make the J work out right.

 

[JedClampett]

Find a copy of the AISC Design Guide 9 (

http://www.aisc.org/Template.cfm?Se.../Ecommerce/ProductDisplay.cfm&ProductID=125).

It explains how to calculate Cw and use it. If you're an AISC member you can download it free, otherwise it's $60.

 

[JStephen]

By the way, "For doubly symmetric I-shapes with rectangular flanges, Cw = Iy*ho^2/4", where ho = distance between the flange centroids. This from section F2 of the new AISC code.

 

[NS4U]

Simply put the warping constant for torsion is analogous to the moment of inertia for bending. It describes how well the flanges will resist warping.

 

[tntn]

just refer to "Cold-formed Steel Design Manual", you'll find the formula to calculate these constants for many kinds of shapes.
Cordially yours

 

[Bagman2524]

I thought the torsional resistance factor K or R was the counterpart to I, not Cw.

 

[NS4U]

You are correct K or R (I think it's called J too?) describes how well the entire section will resist torsion.

In addition to torsion for wide flange (or other open-sections) significant warping stresses can develop in the extremities (ie the flanges) Cw is a factor that describes how well the flanges resist warping.

While the entire section does technically warp, for I sections the amount the web warps in insignificant compared to the flanges.