Improved procedure for equivalent linearization of bridges supported on hysteretic isolators: Fid-Bau Portal

Improved procedure for equivalent linearization of bridges supported on hysteretic isolators

Jara, M. / Jara, J.M. / Olmos, B.A. / Casas, J.R.

Highlights ► An improved equivalent linearization model for isolated bridges is proposed. ► The model improves the prediction capability when it is applied to isolated bridges. ► It can be easily incorporated into DBD framework, and into code specifications. ► Small data scattering was obtained over the whole range of displacement ductility. ► In contrast to other models, it follows the trend of hysteretic energy dissipation.

Abstract Maximum displacement demands can be obtained through non-linear time history analysis, however, many approximate methods have been proposed in recent codes to reduce the required computational time distinctive of non-linear approaches. Some of these methods are based on equivalent linearization of the system by using an effective lateral stiffness (k ef) and equivalent damping ratio (ξ eq). The dynamic characteristics of earthquake ground motions, ductility capacities, type of hysteretic relationships, and stiffness and strength degradation characteristics of the structure are aspects that strongly affect both, the energy dissipation capacity and the effective stiffness of the system; nevertheless, these conditions have not been adequately accounted for in the analyses. This work presents an improved expression, intended for bridges supported on hysteretic isolators, that takes into account some of these aspects. Since lead rubber bearings (LRB) are the most common isolators used on bridges, the expression is focused on the hysteretic behavior of this type of bearing. A simple and rational expression to evaluate the equivalent damping ratio ξ eq, tying the physical behavior of these systems, is proposed. In this way, the prediction capability of the linear equivalent model of bridges supported on LRB isolators is improved. The proposed equation predicts a displacement that is in good agreement with the one obtained through inelastic time history analysis. Furthermore, it can be easily incorporated into the displacement-based design framework, and into the code specifications.