Damage indices for RC columns under three-dimensional excitation

Damage indices are effective in quantifying structural seismic damage. Numerous response-based damage indices have been developed and validated through the hysteretic response of various experimental specimens. However, the accuracy of these indices for evaluating damage of RC columns is challenged by fluctuating axial load and irregular horizontal loading paths from 3-D earthquake excitations. This study introduces D_iem, a material-based damage model for RC columns under random bidirectional loads and variable axial forces. Section damage indices of the plastic hinge are calculated by integrating the damage indices of concrete and steel fiber elements, considering their distance to the centroid axis. The P-Δ effect index is defined, and the component failure index is calculated using a combination of these indices. A hysteretic simulation and D_iem damage analysis program for cantilever RC columns is developed using Fortran. Three RC columns tested under bidirectional hysteretic loading are simulated to calibrate the program. Parameter analysis of 1,638 RC columns is conducted to verify D_iem’s applicability. The results demonstrated that D_iem’s failure assessment aligns with the 80% residual criterion. D_iem analysis of a real seismic damaged RC column shows satisfactory agreement with post-earthquake damage assessment and illustrates significant damage differences between columns with and without axial load fluctuation.