Second-order effects on seismic response of slender bridge columns

This paper presents and discusses, through an experimental investigation, the second-order effects of P-Δ and P-δ on the inelastic seismic response of slender reinforced concrete (RC) bridge columns. Two large-scale RC columns with an aspect ratio (shear span to section width) of 12 were tested under quasi-static cyclic loading. The destabilizing effect of P-Δ and the contribution of P-δ to the growth of the plastic region were experimentally evaluated by comparing primary and secondary moment gradients. Results confirmed the destabilizing effect of P-Δ demands and showed that the geometric second-order effects from P-δ led to a significant increase in the extent of the plastic region (L_pr). Enhancing the strength to compensate for the second-order effects proved to be inadequate to improve the deformation capacity before instability as limited by current seismic design guidelines. Yet, the test columns exhibited stable cyclic response beyond the conventional stability limit indexes.