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Within layered shell objects, straight normals remain straight, which enforces full composite behavior between layers. Straight normals do not necessarily remain normal to the mid-surface, which allows transverse shear deformation. For membrane and bending behavior, quadratic displacement fields are assumed, with appropriate handling to prevent shear locking. Plane-stress behavior is assumed within each layer.
Formulation
Details on the formulation of layered shells are available in the CSI Analysis Reference Manual (The Shell Element > Layered, page 159).
Layered Shell FAQ
- Frequently Asked Questions which concern layered shells are as follows:
Are nonlinear shell objects available?
Answer: Yes, material nonlinearity may be applied to layered shell objects.
What is the multi-axial failure criteria available to nonlinear layered shells?
Extended Question: My understanding is that a failure criteria is necessary to define a yield surface for the multi-axial stress state of brittle and ductile materials. Is the failure criteria Von Mises, Rankine, Tresca, maximum principle stresses, or maximum principle strains?
Answer: Multi-axial failure criteria is not incorporated into the formulation of the nonlinear layered shell objects currently available to SAP2000.
Von Mises stresses, however, are calculated and reported when using the SVM stress-component label. Additional stresses may be calculated by post-processing reported results.
For each direction, redistribution of forces may be modeled according to the nonlinear response of the material stress-strain curve, rather than the multi-axial stress state.
