Stability Index Evaluation of Slender RC Bridge Columns under Seismic and Gravity Loads

This study evaluates the stability index of slender RC bridge columns under seismic and gravity loads. Results from this research indicate that current stability indexes used in neglecting P-δ effects have an associated reliability index that far exceeds values currently proposed in the Caltrans Bridge Design Practice. Reliability indexes were established from a numerical procedure that considered columns with varying ratios of aspect, axial load, and longitudinal and transverse reinforcement. The proposed numerical procedure was extended in defining stability indexes that (1) stipulate threshold limits for neglecting P-δ effects and (2) define a collapse-prevention criterion. Previous studies have investigated reliability indexes for short and slender RC columns by expressing the limit-state function in terms of design moment magnification and second-order analysis methods. The work presented in this study is a departure from these methods because it determines the reliability index based on a limit-state function that explicitly addresses the ductility level at which RC slender columns reach instability under seismic and gravity loads.