On the application limits and performance of the single-mode spectral analysis for seismic analysis of isolated bridges in Canada

Single-mode spectral analysis (SMSA) is a simple procedure efficiently used to evaluate the seismic demands of base-isolated bridges, particularly suitable for the design of simple bridges or preliminary design of complex bridges. However, bridge design codes, notably the Canadian code CSA-S6:19 (CSA-S6 2019), specify many limitations on the use of the method for final design. This paper evaluates the performance of SMSA and the efficiency of its limits of application as specified in the current codes through the results of a parametric study. The hysteretic properties of seismic isolation systems and the stiffness of bridge substructures are varied. Seismic demands predicted by SMSA and nonlinear time-history analyses (NLTHAs) are then compared, both inside and outside the current specified limit range in CSA-S6:19 (CSA-S6 2019). Results show that the most effective application conditions are those related to the maximum equivalent viscous damping and minimum restoring force. The upper limits of the effective period and the post-elastic period can be ignored. Further, to complement SMSA, a relation is proposed to estimate the expected residual displacement as a function of the restoring force at the design displacement. Regression relations allowing estimating the expected mean and confidence interval of the relative displacement deviation predicted by SMSA from that based on NLTHA are also proposed. © 2022 The Author(s).