Direct Displacement-Based Seismic Design and Validation for Hybrid Sliding-Rocking Bridge Substructure Systems
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abstract
In this paper, a direct displacement-based seismic design method for the hybrid sliding-rocking (HSR) segmental bridge piers is presented. The HSR bridges consist of unbonded post-tensioning, end rocking joints and intermediate sliding joints (or slip-dominant joints) along the column height. Joint sliding provides energy dissipation with small damage and control of the applied seismic loading. Residual joint sliding is small and restorable after an intense earthquake event. Force-based seismic design of the HSR columns is difficult to apply because representative R-factors are not available and are difficult to estimate. For this reason, displacement-based design methods are investigated. The proposed method involves an iterative scheme that builds on the capacity spectrum method. In the proposed method, a pushover curve for the HSR columns is computed analytically. Then, the equivalent viscous damping ratio is computed as function of the column displacement. Eventually, the spectral demand obtained from the FEMA 356 is compared to the spectral capacity obtained from the pushover curve are compared. The computed performance is compared with intended performance objectives and iterations are conducted to obtain economical designs. A preliminary comparison of the proposed design method with the results of an experimental study is presented.
