Evaluation of simplified methods for the design of bridges with seismic isolation systems

In this paper, simplified methods for the design of bridges equipped with strongly nonlinear isolation systems (IS) are examined. Reference is made to the single mode method (SMM), adopted in many seismic codes and guidelines for the analysis and design of bridges with flexible substructure. Two different design approaches are considered, one aimed at controlling the maximum force transmitted by the IS to the pier, while the other the maximum pier-deck displacement. The background of the SMM and the implementation of the two design approaches are presented first. This is followed by a series of examples of application and validation studies through nonlinear time-history analyses (NTHA). The variability of the mechanical behavior of the IS with air temperature is taken into account in both design procedures and NTHA. The NTHA results point out that simplified methods of analysis can be reliably used for bridges with IS, to satisfy the design performance objectives over the whole operation range of temperature, once a proper design temperature is selected.