Hysteretic model development and seismic response of unbonded post-tensioned precast CFT segmental bridge columns

The study investigated the cyclic behavior of unbonded, post-tensioned, precast concrete-filled tube segmental bridge columns by loading each specimen twice. Moreover, a stiffness-degrading flag-shaped (SDFS) hysteretic model was developed based on self-centering and stiffness-degrading behaviors. The proposed model overcomes the deficiency of cyclic behavior prediction using a FS model, which self-centers with fixed elastic and inelastic stiffnesses. Experimental and analytical results showed that (1) deformation capabilities of the column under the first and second cyclic tests were similar; however, energy dissipation capacities significantly differed from each other, and (2) the SDFS model predicted the cyclic response of the column better than the FS model. Inelastic time-history analyses were performed to demonstrate the dynamic response variability of a single-degree-of-freedom (SDOF) system using both models. A parametric study, performed on SDOF systems subjected to eight historical earthquakes, showed that increased displacement ductility demand was significant for structures with a low period and low-to-medium yield strength ratio and reduced displacement ductility demand in these systems was effectively attained by increasing energy dissipation capacity.