Dynamic Effects On Seismic Behavior Of Reinforced Concrete Column

As the main bearing component of RC structure, the seismic behavior of reinforced concrete column will be influenced by loading rate. However, there are very few studies on the dynamic properties of the RC members subjected to earthquake loading, and the current seismic design code for buildings hasn’t considered the effect of loading rate on the RC members. In this paper, the effects of loading rate on the RC columns are investigated by using the methods of experimental research and numerical calculation. The main sections of the research work are listed as follows:(1) The effects of loading rate on the dynamic properties of RC columns are experimentally studied with different parameters, including shear span ratio, axial compression ratio, concrete strength, steel strength, longitudinal steel ratio, volume-stirrup ratio, loading mode (uniaxial loading, biaxial loading and variable axial force) and loading rate. The test results show that as the loading rate increases, the yield load and ultimate load increase, and the growth of yield load is higher; the strength degradation, stiffness degradation and damage are faster; the ductility of RC columns decreases; the energy absorption increases slightly. The variable axial force enhances the sensitivity of loading rate of RC columns, and leads to buckling in advance, At the same time, the coupling behavior of the biaxial loading worsens both stiffness and strength degradation. In addition, based on theoretical analysis, as the loading increases, the relative depth of compression zone of RC columns decreases; the growth on the flexural bearing capacity of RC column is far higher than that of the shear bearing capacity; and the failure mechanism has also changed.(2) The effects of loading pattern (uniaxial cyclic loading, cross loading path, rhombus loading path and circular loading path) on the dynamic properties of RC columns are studied experimentally. The test results show that the combination of loading path and loading rate leads to enhancement of strength degradation, stiffness strength and the decrease level of ductility. Based on the calculation of equivalent damping, it is observed that the strongest energy dissipation occurs in the circular loading path. As the loading rate increases, the slope of skeleton curve decreases more quickly in the later stage of loading, especially in the rhombus loading path. Moreover, the empirical formulas of equivalent damping under static and dynamic loading are proposed by regression analysis of test results. (3) Based on the force-based beam-column element with distributed plasticity in OpenSees, the loading processes under monotonic and earthquake loading are simulated with different strain rate of materials, and the empirical formulas of ultimate bearing capacity are proposed according to the simulation results. Furthermore, in order to simulate the dynamic properties of RC column subjected to earthquake loading, based on the Beam with Hinges Element in OpenSees, considering the influence of different factors (strain rate effects of materials, the interaction between biaxial bending and axial force, the shear effect, the bond-slip effect), a Tcl program is compiled, and the dynamic behavior of RC columns under different loading paths are simulated. The results show that the Tcl program can simulate the hysteretic behavior of RC columns well.