The structural analysis for crashworthiness, presented in this paper, consists of three parts: thin-walled element modeling, stiffness formulation and numerical solution. In thin-walled elements the stresses rarely reach the yield level and the element's force-deformation relationship is usually controlled by local buckling and subsequent collapse of the section. This relationship can be generally divided into four regimes: linear, post-buckling, crippling and deep collapse. In the post buckling regime only a part of the section contributes to its load carrying capacity and it is this effective part that is being used to calculate the section properties. In the deep collapse regime the stiffness is calculated by considering an appropriate mechanism of section collapse. The element stiffness is then assembled into the structural stiffness matrix. A finite element computer program is developed, incorporating this concept, for the crash simulation of general 3-dimensional structures. The program uses step-by-step solution procedures for the inelastic analysis and the constant-energy incremental loading method for loading increments. The analytical results show a promising agreement with the test data.