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Hello,

I have modelled a masonry arch bridge using Elastic Plate Membrane sections and both ASDShellQ4 and ShellDKGT elements, but the stress in the elements is not being recorded in Post Processing. I am utilizing "section.fiber.stress" in the MPCORecorder, but have also tried a few other custom commands. I have tried a few suggestions from the forum, and updating the solvers, to no avail. I am only analyzing it under self-weight for now, so I am doing a static analysis. I am able to visualize section forces and displacements fine.

I have attached the model here. Any suggestion or advice is appreciated.

Thanks!

It's because the ElasticMembranePlateSection, assuming an elastic behavior, works directly with analytically integrated section forces, it does not perform numerical integration of stresses using fibers.

For example, given the equation for the membrane force in the X direction:
F_xx = integrate(Sigma_xx, -H/2, +H/2), where H is the thickness of the cross-section

For an ElasticMembranePlateSection it is F_xx = E*H*strain_xx
For a generic nonlinear section, LayeredShell or PlateFiber, it is: F_xx = SUM(Sigma_xx_i * H_i, for each fiber_i)


Due to the fact that the ElasticMembranePlateSection does not have fibers, you cannot record Stresses.
If you want, you can create an Elastic 3D material and put it into a nonlinear shell section (one of the above mentioned). But the computation will be more expensive.

Otherwise, just record section forces. By the way, I think you are only interested in membrane forces. If so, your thickness is 1, so the section force actually coincide with the stress

Thank you so much! This was a theory, but I could not find the formula by which the section force was calculated.

You're welcome