Hybrid-Mixed Stress Finite Element Models for the Dynamic Analysis of Reinforced Concrete Frame Structures

This communication presents a hybrid-mixed stress model for the physically non linear dynamic analysis of concrete structures [3]. In this model, both the stress and the displacement fields are approximated in the domain of each element. The displacements along the static boundary are also independently approximated. Orthonormal Legendre polynomials are used as approximation space functions. The use of these functions enables the use of analytical closed form solutions for the computation of all elastic structural operators and leads to the development of very effective p-refinement procedures. To model the concrete physically non linear behaviour it is adopted the damage model introduced by Mazars [18]. To validate and demonstrate the potential of the model, several numerical examples are presented and discussed [2], in which displacement conventional finite elements (CFE) are compared with hybrid-mixed stress models. A mixed formulation is used to develop a higher-order incremental method for time integration. The displacement, the velocity and optionally the acceleration fields are independently approximated using hierarchical orthonormal Legendre polynomial bases [12]. The accuracy and the efficiency of this technique are assessed by comparing the obtained results with those provided by the classical Newmark method [21] in nonlinear dynamic analysis [20].