Hybrid Models

Abstract

This chapter presents the idea behind the formulation of the element stiffness matrix based on the assumed stress hybrid model using the principle of minimum complementary energy. The general formulation of the hybrid stress model is then introduced based on a modified complementary (variational) principle that permits discontinuities of the stresses along the interelement boundaries. In formulating the element stiffness matrix by the compatible model, displacement functions within each element are interpolated in terms of nodal displacements in such a manner that complete compatibility with the neighboring elements is enforced. In applying the hybrid stress model in finite-element analysis, it is important to make an appropriate choice of the assumed stresses in the element and the assumed element boundary displacements. The use of more boundary displacement modes with the same linear moment distribution can only yield more inaccurate solutions corresponding to more flexible structures.