Failure Mechanism Analysis of Long-Span Continuous Rigid-Frame Bridge with Large and Different Pier Heights Using the Generalized Bouc–Wen Hysteresis Model

Continuous rigid-frame bridges (CRFBs) with tall and short piers have been extensively constructed in mountainous areas. The nonlinear seismic responses and failure mechanisms of CRFBs are more complex than those of conventional bridges. The fiber beam model is typically used to simulate the constitutive behavior of component sections at a high computational cost and imposes complex modeling and substantial computational demands during the nonlinear analysis of the entire bridge. In this study, a numerical model was developed to simulate effectively and accurately the nonlinear behavior of CRFBs using the generalized Bouc–Wen model, considering the strength degradation, stiffness degradation, and pinching effects. The plastic and degradation behaviors were regulated by the parameters of the Bouc–Wen model. Using a six-span CRFB with tall and short piers as an example, the longitudinal and transverse seismic responses and failure mechanisms of the piers of a CRFB under near-fault and far-field (FF) motions were analyzed. The numerical results indicated that the piers entered the yielding state in the order of increasing pier height under longitudinal excitation conditions. Different yielding sequences of the piers in the transverse direction were identified depending on the type of ground motion and the dynamic characteristics of the tall and short piers. The failure mechanisms were verified by comparing the curvature, moment, and shear force distributions of the tall and short piers. Significant effects of the high-other modes on the responses of the high-height piers were observed, particularly for the pier under FF ground motion in the transverse direction.