Test And Simulation On Dynamic Behavior Of RC Columns With Different Reinforcement Ratios Considering Strain Rate Effects

The precise prediction of mechanical properties and behavior of reinforced concrete (RC) columns under dynamic loadings such as severe earthquakes or strong winds is crucial to aseismic design of civil engineering structures. In traditional aseismic design code,the effect of strain rate on materials strength, load carrying capacity, deformation, energy dissipation capacity and failure mode of structural members are not considered properly. Even though tests on dynamic behavior of reinforced concrete members under high strain rate have recently been carried out, there is a far way to accumulate enough test results to understand the dynamic performance of RC structures and members.This paper describes the seismic behaviors and numerical method of reinforced concrete columns under fast loading. The main achievements can be summarized as follows:(1) Experiments of three reinforced concrete columns with various reinforcement ratios under constant axial loads and fast cyclic lateral reversed loads are presented in this paper. Meanwhile, the characters of hysteretic loops, skeleton curves, displacement ductility coefficient, energy dissipation capacity and the failure mode at different loading rate are studied, and the experiment results can be provided for the nonlinear analysis of the reinforced concrete columns.(2) Numerical simulations on the dynamic behavior of a typical RC column specimen under monotone dynamic loading were performed. A recently developed constitutive model of concrete considering the strain rate effect was introduced into a dynamic fiber model to characterize the nonlinear strain rate dependent behavior of concrete. The effects of second order, plastic hinge zone and shear deformation are considered in the fiber model. Then the developed dynamic fiber element model is validated by comparing the simulated results of RC column specimens with the test results reported in related literatures and the fast loading test results in this paper. Results show that the developed fiber element model can predict the behavior of RC columns with acceptable accuracy. Especially in the model considered shear deformation, the simulated deformation capacity is much closer to the experimental results.(3) The dynamic properties of the RC column considered the influence of reinforcement ratio were simulated. Utilizing the developed model, the ultimate bearing capacity of columns with various longitudinal reinforcement ratios and volumetric stirrup ratios were investigated. As the loading rate increases, the ultimate carrying capacity and stiffness of columns, with various hoop or longitudinal reinforcement ratio, also increase; the ultimate bearing capacity growth factors relative to static loading of the specimens with lower volumetric stirrup ratios are smaller than the ones with higher ratios; the ultimate carrying capacity growth factors relative to static loading of the specimens with higher longitudinal reinforcement ratios are smaller than the ones with lower ratios. It is found the differences of simulated ultimate carrying capacity between the model considering the shear deformation and the model not considering are minute.(4) Utilizing an innovative smart aggregate approach based on piezoceramic, damage status of one column in the fast loading experiment was monitored. According to the measured signal, wavelet-packet-based damage index evaluates the damage development in concrete columns under fast loading. The experimental results show that the developed smart aggregate-based approach can effectively evaluate the health status of concrete columns during the loading procedure.