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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.


h1. Formulation

* Additional details on the formulation of layered shell elements are available in the {new-tab-link:http://www.csiberkeley.com/}CSI{new-tab-link} [_Analysis Reference Manual_|doc:CSI Analysis Reference Manual] (The Shell Element > Layered, page 159).


h1. Layered Shell FAQ

Frequently Asked Questions which concern layered shells are as follows:


h2. Are nonlinear shell objects available?

*Answer:* Yes, [material nonlinearity|kb:Material nonlinearity] may be applied to layered shell objects.

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As of SAP2000 V14.0.0.
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h2. 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|kb:Nonlinear] layered shell objects currently available to [SAP2000|sap2000:home].

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.

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*Related Incidents:*
* {incident:no=23755|comment=Multi-axial failure criterion for nonlinear shell elements.} \\
* {incident:no=42191|comment=Multi-axial strength criterion for concrete.} \\
** {email:date=2/1/2012|from=ok|to=ed|subject=Multi-axial strength criterion for concrete|comment=|id=8585217}
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h1. See Also

* [Nonlinear layered shell|kb:Nonlinear layered shell] article