Reinforced Concrete Structures under Cyclic Loading

Experimental programs in laboratories give real results to identify nonlinear behavior of reinforced concrete (RC) structures but they are limited to knowledge of particular cases under restricted structural dimensions, sizes, shapes, loading and boundary conditions but the computational simulation approach has no limit to its application. Constitutive models are developed to simulate the dynamic nonlinear response of concrete and steel reinforcement subjected to cyclic loading varying randomly in magnitude. The behavior of structural concrete under monotonic loading is affected by important material aspects including cracking, crushing, tension stiffening, compression softening and bond slip. Reversed cyclic loading introduces further complexities such as stiffness degradation in concrete and the Bauschinger effect in reinforcing steel. In this research the validity and reliability of some proposed constitutive models for concrete considering general loading i.e. cyclic, monotonic, partial, common point and transition loading are evaluated. Amongst many existing constitutive models, because of their simplicity and common usage in the finite element analysis of RC structures, only some common proposed models based on nonlinear elasticity-based approach are investigated. These models are verified against experimental data available in the literature and the results are discussed. In this study, also, a hysteretic stress?strain model is developed for unconfined concrete with the intention of providing efficient modeling for the structural behavior of concrete in seismic regions. The proposed model is based on the findings of previous experimental and analytical studies. The model for concrete subjected to monotonic and cyclic loading, comprises four components in compression and tension; an envelope curve (for monotonic and cyclic loading), an unloading curve, a reloading curve, and transition curve. Also presented are formulations for partial unloading and partial reloading curves. The proposed Constitutive model reliability is investigated by RC members non-linear finite element analysis (FEM) using by finite element software ABAQUS. Comparisons with test results showed that the proposed model provides a good fit to a wide range of experimentally established hysteresis loops.