Development and verification of a new OpenSees element model for a two-stage friction pendulum bearing

Bridges play a critical role in transportation infrastructure, and ensuring their safety is a key concern for structural engineers. Various seismic isolation techniques have been introduced to mitigate the impact of earthquake forces. The unavailability of novel isolation elements in commercial software makes it difficult to implement in real-world structures. This study presents the development and verification of a two-stage friction pendulum bearing (TSFPB) nonlinear element model within the OpenSees environment. The TSFPB comprises only two sliding stages, designed to accommodate different-intensity earthquakes, rendering it suitable for both moderate and severe earthquakes. A theoretical model of the TSFPB is first presented to illustrate its working mechanism. Based on this, a nonlinear element model for TSFPB is developed in C++ and integrated into the OpenSees framework. Additionally, a numerical model is developed in ABAQUS to assess the stability and stress condition before prototype development. Comprehensive laboratory tests are conducted to verify the accuracy of the OpenSees, theoretical and ABAQUS models. The results demonstrate the remarkable accuracy of these models with experimental results, maintaining the discrepancy below 10%. These findings confirm the accuracy of the TSFPB nonlinear element and highlight its potential for advanced seismic isolation design.