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Warping Boundary Condition

Question:

I'm trying to understand when I should use the warping boundary condition. For fully fixed supports it is restrained similar to the other degrees of freedom. I am modeling a bridge with piers on pile foundations, if the piles are bearing in soil, technically they are not restrained from torsional movement, does that mean I would not apply a torsional restraint. However, if you had drilled shafts in rock they would be restrained in the torsional DOF?

Answer:

Dear Sir,

Greetings!

Thank you for your patience. Sorry for the delay in response.

If the member is allowed to warp freely, then the applied torque is resisted entirely by torsional shear stresses (called St. Venant's torsional shear stress). If the member is not allowed to warp freely, the applied torque is resisted by St.Venant's torsional shear stress and warping torsion. This behavior is called nonuniform torsion.

The warping restraint prevents the warping deformation. When warping deformation is constrained, the member undergoes non-uniform torsion. This restraint will be only effective when the warping effects are considered in the section data:

However to in circular pile sections there will be no warping. So in this case the torque will be resisted by uniform torsion. In that case the restraint need to be provided in the direction of application of torque (Rx,Ry,Rz)

Hope this clears your doubt. Kindly let us know if any further assistance is needed.

Regards,

Anuj Asati

Global Technical Center

Question:

Could you provide an example of when you would want to provide a warping constraint?

Answer:
Hi Sir,

Greetings!

Here with I have attached a model file where I have modeled 3 cantilever beams.

Beam 1 has section property where warping is not considered:

Beam 2 and beam 3 has section property with warping effect consideration:

For beam 2 warping restraint is not provided and for beam three it is provided:

As it is a channel section lateral torsion buckling (LTB) will occur but it will not be captured in beam 1 as for beam 1 warping effects are not considered.

However for Beam 2 and Beam 3 warping due to LTB will occur but for beam 1 it will only be resisted by uniform torsion (Mt) as warping is not constraint. Whereas for beam 3 warping due to LTB will be resisted by combination of uniform (Mt) and non- uniform torsion (Mw):

Hope this clears your doubt. Kindly let us know if any further assistance is needed.

Regards,

Anuj Asati

Global Technical Center

Creation date: 11/1/2019 5:25 AM Updated: 11/6/2019 10:28 AM

warping example 1.mcb

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	warping example 1.mcb 62 KB