NONLINEAR ANALYSIS OF REINFORCED CONCRETE STRUCTURES UNDER MONOTONIC AND REVERSED CYCLIC LOADING USING THE FINITE ELEMENT METHOD

In this study, for predicting the behavior of reinforced concrete structures under monotonic and cyclic loading, a nonlinear finite element analysis has been used. For simulation of the nonlinear behavior of concrete under pressure and tension, the hierarchical single-surface (HISS) plasticity model has been used that can take into account elastic and plastic deformations. It involves a single continuous yield surface, unlike some previous models that include multiple and discontinuous yield surfaces, which can introduce computational diculties. This model, which allows for isotropic and anisotropic hardening and associated and non-associated plasticity characterizations, can be used to represent material responses based on the continuum plasticity theory. Cyclic and repetitive loading, involving loading, unloading and reloading, occur in many problems, such as dynamics, earthquakes and thermo-mechanical responses. The unloading response is often nonlinear, However as a simpli- fication, it is often treated as linear elastic. Here, both  linear and nonlinear elastic simulations are included. During unloading and reloading, Plastic deformations can occur and can in uence the overall response of the structure. In this study, the Desai equations, which that are simple but can provide satisfactory simulation for the unloading and reloading states of reinforced concretes under cyclic loading are used. The elastic-perfectly plastic behavior of steel reinforcement is assumed. Then, in order to study the capability of the proposed models in the analysis of nonlinear finite elements of reinforced concrete structures under monotonic and cyclic loading, a program was written in FORTRAN language in a framework of the finite element. This program used eight- noded serendipity elements for concrete and twonoded elements for reinforced concrete. In order to study the capability of the proposed model in predicting the behavior of reinforced concrete structures under monotonic and cyclic loading, one beam and one frame have been modeled and the results of the load - displacement were found for them. Comparison between the loaddisplacement obtained from these structures with laboratory results show good agreement, and shows the capability and potential of the present model in investigating the nonlinear behavior of reinforced concrete structures.