Recommended Parameters for Takeda Degrading Stiffness Hysteresis for Reinforced Concrete Circular Bridge Columns

An accurate estimation of the seismic demands on bridges depends on, among others, the correct assumption of the column's force-displacement hysteresis. However, there is little guid-ance in seismic codes regarding the choice of a hysteretic model for nonlinear analysis of bridges containing reinforced concrete (RC) circular columns. This paper addresses this shortcoming by proposing the unloading (alpha) and reloading (beta) factors for the Takeda degrading stiffness hysteretic model that may be employed for the nonlinear time-history analysis of bridges containing circular RC columns. These recommendations were obtained through analysis of the reloading/unloading stiffnesses and the energy dissipation of 24 previously conducted cyclic quasi-static tests of circular RC columns. Moreover, evaluation of the hyster-etic damping of the experiments allows an equation to estimate the equivalent viscous damping as a function of displacement ductility level to be introduced. A sensitivity analysis on the mean values of analysis results shows an impact of up to 20% in terms of peak deformation demands.