Evaluation of plastic hinge models and inelastic analysis tools for performance-based seismic design of RC bridge columns

For over 50 years, the notion of an equivalent region under constant plastic curvature, i.e., the plastic hinge length (Lp), has been the main approach for evaluating the inelastic response of reinforced concrete (RC) columns for seismic bridge design. Most of the proposed Lp models have been calibrated on columns with modest slenderness to predict ultimate displacement. However, modern design approaches require predicting intermediate damage levels, or limit states, and urban congestion is leading to increasingly slender columns; thus bringing doubt on the reliability of plastic hinge models. The performance of Lp models in lumped plasticity elements was assessed by conducting analyses on 34 columns from the PEER Column Database. Results show that the Lp definition in lumped plasticity analyses produces drastic and random differences for varying limit states. Distributed plasticity elements can capture inelastic global and local response throughout the element without explicit definition of an inelastic zone. Lumped and distributed plasticity elements were thus assessed by comparing the global and local responses for five columns of increasing slenderness; the most slender of which was constructed and tested as part of this research to expand the current database for slender columns. Performance was found to be sensitive to aspect ratio; indicating behavior controlled by P-delta effects. The study has highlighted the need for a unified definition of limit states, as well as improved methods to accurately and efficiently predict inelastic behavior at each limit state. Inaccuracy in current numerical tools was found not only at intermediate limit states but also when predicting the global behavior of slender columns.