The design provisions for seismically isolated bridges in the CAN/CSA-S6 Canadian Highway Bridge Design Code and the AASHTO Guide Specifications for Seismic Isolation Design ( AASHTO 2010 , 2014 ) have been developed primarily based on ground motions recorded along the west coast of North America. Both codes include a simplified analysis procedure that relies on an equivalent effective linearization of the nonlinear isolated structure together with damping coefficients to account for the effect of energy dissipation on the response of the isolated system. The appropriateness and range of application of code-specified simplified methods were investigated through nonlinear time-history analyses to propose improvements to this procedure for the new edition of the CSA-S6-2014 code. Based on these analyses, new damping coefficients are proposed for Eastern North America (ENA) and new limits for the application of the simplified method are defined. For ENA, the method with newly proposed damping coefficients can give good bridge displacement estimates for equivalent damping ratios of up to 40%, which broadens the possible designs that can be achieved using the simplified method. This study also showed that applicability limits could be defined more accurately as a function of the system properties.
Improvements to the simplified analysis method for the design of seismically isolated bridges in CSA-S6-14
