2-D Nonlinear Finite Element Analysis Of Reinforced Concrete Members

In the analysis of reinforced concrete structures subjected to general loading conditions, the realistic constitutive model and the robust analytical procedure are two key preconditions to produce reasonably accurate simulations of nonlinear behaviors of such structures. Rational constitutive models for concrete and reinforcement are required to reflect the behaviors of such materials under complicated stress conditions.Based on the available testing data and research results, constitutive model of concrete under reversed cyclic loading is refined in this thesis.The path of the unloading and reloading curves of concrete can accurately reflect the energy dissipation characteristics of concrete, as well as the damage of the material due to loading reversals. Partial unloading or reloading rules can also be considered, as structural components may partially unload and then partially reload during a seismic event. Local contact effect of cracked concrete is taken into account. An equivalent uniaxial strain model is used to describe the stress-strain relationship of concrete under complex stress conditions.Based on the above-mentioned work of modeling, a two-dimensional nonlinear finite element for reinforced concrete was added to the user-defined element library of FEAPpv, which is used to analyze reinforced concrete structures subjected to general loading conditions, both monotonic and reversed cyclic loadings. The following work has been carried out in this thesis:①The four-noded isoparametric quadrilateral finite element is added to the user- defined element library of FEAPpv. As it is conventionally done, the steel is assumed"smeared"throughout the concrete. The element tangent stiffness is formed numerically usually using a two by two (or three by three) grid of Gaussian integration points.②Based on the smeared crack model and the equivalent uniaxial strain model, a hysteretic stress–strain relationship of concrete is defined. The influence of Poisson ratio and biaxial stress states of concrete is taken into account.③In addition, constitutive model of steel considering the Bauschinger effect is implemented, in which the kinamatic hardening can be considered.④Effect of different evaluation schemes of the shear modulus of cracked concrete is taken into account.⑤Local contact effect of concrete on the hysteretic behavior of shear panels under reversed cyclic loading was discussed in detail.⑥61 shear panels and several shear walls subjected to monotonic or reversed cyclic loading were simulated.The major conclusions are summarized as follows:①The simulation of 61 shear panels has shown that the prediction of ultimate bearing capacity and deformation capacity using the program has good agreement with the tested results, which verifies the validity of the modeling.②The evaluation schemes of shear modulus of cracked concrete has significant effect on the analyzed results of ultimate bearing capacity and deformation capacity as well.③Inclusion of local contact effect in tension–compression regions in the stress-strain relationship of concrete yields more accurate results.④The application of the program can be extended to analyze wall epecimens subjected to reversed cyclic loading,the analytical results agrees with that of experiments.