To investigate the efficiency of passive energy dissipation devices in protecting cable-stayed bridges from severe damage when subjected to high-intensity ground motions, a 1/20-scale bridge model from a typical medium-span concrete cable-stayed bridge was designed, constructed, and tested on shake tables. Yielding steel damper (YSD) and viscous fluid damper (VFD) were used as passive energy dissipation devices in the transverse and longitudinal directions, respectively. The bridge models were then excited by two ground motions with different spectral characteristics in transverse and longitudinal directions accordingly, including the Chi-Chi earthquake wave and a site-specific artificial wave. The seismic responses of the bridge models with and without the passive devices were analyzed and compared. Both numerical and test results show that the YSD applied in the transverse direction could reduce the seismic responses of the towers effectively, and the VFD applied in the longitudinal direction co...

Viscous dampers are usually installed between the tower and girder to restrain the girder’s longitudinal displacement of cable-stayed bridges. Yet the appropriate damper design has to be determined through repetitive numerical analysis in the current practice. To streamline this process, analytical formulas were derived with a proposed 3 degree of freedom simplified model based on equivalent damping ratio and linearization of nonlinear viscous dampers, for achieving the damping coefficient of nonlinear viscous dampers of the cable-stayed bridge under near-fault ground motions, and the accuracy is verified by numerical analysis of a real cable-stayed bridge model.

Bidirectional shake-table tests were performed on two types of relatively large two-span continuous elevated-girder bridge models. One was supported on thin-walled hollow steel (HT) piers, and the other was supported on concrete-filled tubular (CFT) piers. The CFT piers were made by filling the hollow columns of the HT piers with normal concrete. One objective of the shake-table tests was to acquire basic data to establish an advanced seismic design method of the HT and CFT piers under bidirectional horizontal seismic accelerations, considering the interaction between the piers, rubber bearings, and a superstructure. The other objective was to experimentally confirm the effectiveness of upgrading the elevated-girder bridges with the HT piers by using CFT piers. It was shown by the present tests that the ultimate state of the respective HT piers in the bridge model was predicted reasonably well by the interaction equation expressed in terms of the multiaxial force and moment components acting at the top of the columns. As soon as all the piers reached their ultimate states, the entire physical bridge model with the HT piers started to collapse in the transverse (TR) direction. Because of the load redistribution between the HT piers in the bridge model during the shake-table test, the energy dissipation capacity of the piers increased considerably compared with that evaluated by the conventional shake-table test on single cantilever column models with a mass fixed to their top. The physical bridge model with the CFT piers exhibited an excellently upgraded seismic performance (i.e., small local buckling deformations of the piers and negligibly small residual sway displacements of the bridge system) despite the increased input acceleration wave with an amplitude 1.5 times larger than that used for the physical bridge model with the HT piers. This upgraded performance of the CFT piers was due to their enhanced energy dissipation capacity and unique local buckling restraining and/or restoring behavior.

The displacement-based seismic-design (DSD) methods, owing to their simplicity and efficiency, have been more and more recognized in structural seismic-research communities during the past few years. However, the dynamic P-Δ effect, as has long been well realized to be a key issue in structure earthquake engineering that could amplify the structure’s seismic responses or even trigger the structure’s instability, is still not well solved practically because of the complicated nonlinear mechanism. Therefore, in aim to achieve a practical and general purpose solution to consider the P-Δ effects in various DSD methods for single-degree-of-freedom (SDOF) systems, first, the existing approaches of considering P-Δ effects in current seismic analysis and design were evaluated by carrying out a large set of nonlinear time-history analyses, and then new design formulas and recommendations on threshold of neglecting P-Δ effects and the allowable design thresholds were promoted on the basis of the statistics ...