Composite finite elements in structural analysis

The paper concerns mixed finite element models and experiments their capability in the analysis plastic collapse of both plane and three-dimensional problems respectively. The models are easy to formulate and implement because are based on simple assumptions for the unknown fields. A composite triangular or tetrahedral mesh is assumed over the domain. Within each element the displacement field is described by a quadratic interpolation, while the stress field is represented by a piece-wise constant description by introducing a subdivision of the element into proper sub-regions. The plastic collapse analysis is formulated as a mathematical programming problem and is accomplished by an Interior Point algorithm which furnishes both the collapse multiplier and the collapse mechanism. A series of numerical experiments shows that the proposed models perform well achieving the favorite context in plastic analysis, taking advantage of the absence of volumetric locking and the possibility of allowing discontinuities in the stress field within the element.