# Discrepancy in Element Stiffness Matrix Output using Substructure Approach

**URL:** <https://calculix.discourse.group/t/discrepancy-in-element-stiffness-matrix-output-using-substructure-approach/2007>\
**Category:** Uncategorized\
**Created:** [January 4, 2024, 6:00am UTC](https://calculix.discourse.group/t/discrepancy-in-element-stiffness-matrix-output-using-substructure-approach/2007 "2024-01-04T06:00:42Z")\
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**Author:** ![vicmw](https://avatars.discourse-cdn.com/v4/letter/v/6de8d8/32.png) [@vicmw](https://calculix.discourse.group/u/vicmw)\
**Post date:** [January 6, 2024, 6:22pm UTC](https://calculix.discourse.group/t/discrepancy-in-element-stiffness-matrix-output-using-substructure-approach/2007/29 "2024-01-06T18:22:27Z")

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@Disla That seems pretty bad CPS4 has non-zero ZZ stress. I tried refining the mesh and the ZZ stress increases! Seems like you have to use orthotropic material to get actual plane-stress in a CPS4 element?

S4 shell doesn’t seem to have this problem and is maybe a better “plane stress” element?

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