Equivalent linearization of bridges with bilinear isolation systems

Although maximum displacement demands of bridges can be obtained through non-linear time history analysis, many approximate methods have been proposed in recent codes to reduce the required computational time distinctive of non-linear approaches. Among these methods, equivalent linearization method is best known. This paper evaluates the accuracy of equivalent linearization method adopted in AASHTO through comparison of non-linear and linear time history analysis. The isolation system is characterized by bilinear hysteretic behavior and the bridge is simplified to be a single-degree-of-freedom (SDOF) system. A comprehensive parametric study is performed using a program developed by MATLAB in combination with OpenSees. Results show that the predicted maximum displacement is significantly underestimated by AASHTO method when the strain hardening ratio and ductility ratio are relatively small. To improve the estimation accuracy of equivalent linearization technique, a new equation of equivalent damping ratio is proposed by modifying AASHTO method. © 2014 Taylor & Francis Group.