"The earthquake-resistant design of bridges requires inelastic deformations in columns to dissipate seismic energy. Reinforced concrete (RC) bridge columns are thus designed to exhibit a stable ductile inelastic response when subjected to earthquakes. Previous research on the inelastic response of RC bridge columns have led to current seismic design specifications. Yet, the slenderness effects on the inelastic response of RC bridge columns have not been adequately addressed. In this research, the second-order effects of slenderness, namely, P-Delta and P-delta moments on the inelastic response of slender RC bridge columns are experimentally evaluated. Four largescale RC columns with aspect ratios (shear span length to section width) of 10 and 12 were tested under axial and lateral loads. The destabilizing effect of P-Delta and the contribution of P-delta to the extent of the critical plastic region along columns height were experimentally evaluated. It was found that the test columns exhibited stable cyclic response beyond the conventional stability limit indices, despite the destabilizing effects of P-Delta moments. Experimental results also showed that the second-order P-delta moments lead to a significant increase in the length of the plastic region (Lpr). Experimental Lpr values were compared against North American, European, and New Zealand design guidelines. It was found that all design codes considered in this study significantly underestimated Lpr, except for the seismic design provisions provided by Caltrans. Previous expressions for the length of the plastic region were reexamined in light of the new experimental data and strong disagreement between experimental and predicted Lpr was observed. A study on the capability of continuum-based finite element (FE) models for predicting seismic damage in reinforced concrete (RC) bridge columns is presented. Experimental data from 4 largescale columns, under quasi-static reversed cyclic loading, were used to verify the FE results at two levels of global and local structural responses. Statistical measures for goodness-of-fit were utilized to quantitatively evaluate the accuracy of the FE models in addition to the conventional method of visual comparison of overlaid plots. Seismic damage states were predicted from the simulation results and compared against experimental observations from tests. 3D FE simulations were proved to be capable of simulating seismic damage in slender RC columns. Analytical expressions and closed-form solutions to the effects of slenderness and second-order moments on the inelastic response of RC columns are presented. A mathematical expression for the length of the plastic region (Lpr) in slender RC columns, which is significantly affected by nonlinear second-order moments, is presented. Nonlinear beam-column theory in conjunction with a bilinear inelastic moment-curvature response was utilized to determine the magnitude by which the inelastic response of RC columns is affected by their slenderness. Also, a slenderness limit for RC bridge columns is defined in terms of design variables, beyond which the second-order effects on the inelastic response of RC bridge columns are significant and can no longer be ignored. A parametric study was conducted on all the possible design configurations that are permitted by current seismic design guidelines for bridge columns to evaluate the sensitivity of RC bridge columns to second-order effects. Recommendations are made to update the current design guidelines for consideration of the second-order effects. Furthermore, simple design formulas are proposed to predict the maximum P-delta moment and its impact on the length of the plastic region."--Pages ii-iii.
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