Efficient Response Estimation Approach for As-Built Bridges Based on Multisupport Response Spectrum Method

Assessing the postdisaster seismic responses of the as-built bridges based on their real-time status is critical to maintaining their seismic capacity and planning retrofits. This task requires a fast and accurate identification and response estimation method, whereas existing methods either adopt model updating requiring detailed design archives or request sophisticated site testing, both of which are time-consuming and labor-intensive. In this study, approaches combining system identification methods with response spectrum methods for bridges are investigated. A general state-space representation for bridges considering multisupport excitation is developed for model identification. The assumption of the boundary damping matrix in the multisupport response spectrum (MSRS) method is investigated and proved to eliminate pseudo-damping for general viscous-damping structures. A hybrid frequency fitting method (HFF) and subspace system identification method (SSI) in the time and frequency domains, respectively, are examined, and approaches to extracting equivalent boundary stiffness and damping from the identified structural models are studied. The MSRS method is adapted to both identification methods. Numerical simulations and experiments are used to validate the identification approaches in the estimation of boundary conditions. The models identified from the shake table experiments are further used in evaluating its seismic responses. The results of the MSRS method are compared with those from the spectral analysis method showing that the HFF method performs well both in identifying the bridge model and estimating the structural responses. Whereas, the SSI-based methods fail to give a good estimation of boundary damping, and thus cannot directly apply to the MSRS method.