GSA – Quad 4 MITC elements or Quad 8 elements?
As a general guide:
The quad 8 (and tri 6) elements provide a quadratic approximation of displacement over their element domain and so provide the best accuracy when compared with the linear approximation of quad 4 (and tri 3) elements. The 8 nodes required to accommodate quadratic behaviour makes such elements the most numerically expensive in terms of processing time, memory requirements and stored file size. Where such constraints are not an issue, quad 8 elements offer the best performance.
The quad 4 and tri 3 elements in contrast provide only a linear approximation of displacement over their domain and so while less accurate, their requirement for only 4 nodes per element make such elements an attractive practical alternative. This alternative becomes more relevant from GSA 8.5 with an improvement to the out-of-plane performance of linear elements by the introduction of the MITC formulation. This new formulation removes the previous problems of hourglassing associated with the original ‘Mindlin’ formulation and so, while still linear in approximation, offers a competitive alternative to the quadratic elements.
There are two locations where you can set the usage of the MITC elements:
- for all new analyses – Tools | Preferences | Miscellaneous | GSS Solution | Plate formulation default
- for existing or particular analyses – Analysis task | Advanced | 2D Element Analysis | Plate formulation