More than 40% of bridges in Southwest China have piers over 40 m height. The seismic behaviour of these bridges is critical, especially exposed to near-fault pulse-like ground motions. This paper conducts fragility analyses to assess the seismic vulnerability of tall pier bridges under near-fault motions. Fragility curves are developed for a typical 50-m tall pier and a 10 m conventional pier with probabilistic seismic demand models (PSDMs). When developing the PSDMs, curvature ductility at pier base is used as the demand parameter; the 5% damped spectral acceleration of the fundamental period (S_a(T₁, 5%)) is employed as an intensity measure of the motions. Results show that the 50 m pier is less vulnerable than the 10 m pier under both the near-fault and far-field motions and is unlikely to collapse in real earthquake events. Furthermore, the seismic fragility of the 50 m pier is found highly related to the pre-defined damage state capacities, indicating that the damage states should be carefully specified to properly estimate the vulnerability of tall piers. Finally, analyses are conducted for piers with heights of 40, 60, 70, and 80 m, extending the conclusions obtained from 50 m pier to a class of tall piers.

Energy dissipation bearing (EDB) is a conventional steel bridge bearing in connection with well designed mild steel dampers. Seismic performance test was undertaken for both damper units and a prototype bearing, and the results show very stable and high dissipation characteristics. In describing the hysteretic behavior of EDBs, the Wen model is proved to be more reasonable, and the corresponding model parameters are also proposed according to the test results. EDBs have been applied in the seismic control of a long span bridge, the Nanjing Jia River Bridge, for the first time, in both the longitudinal and transverse directions. Sensitivity studies were conducted to investigate the effectiveness and to determine the optimum parameters and distribution of the EDBs through nonlinear time-history analysis. The results show that EDBs achieve a very high effectiveness in seismic control, in both the longitudinal and transverse directions. Compared with other damping devices, they can provide a simple but valid ...

This work focused on the damping effectiveness of additional longitudinal viscous dampers employed for seismic control of long-span cable-stayed bridges considering wave passage effects. A 1/35-scale physical model scaled from a typical long-span cable-stayed bridge was designed, constructed, and tested on four shake tables. The seismic responses of the systems with and without viscous dampers, under different types of ground motions considering uniform or traveling wave excitations, were analyzed and compared. The test results show that the damping effectiveness of the additional longitudinal viscous dampers was significantly reduced under near-field ground motion. The wave passage had a great influence on the displacement responses of the towers and the deck and the relative variation amplitudes of the cable forces near the midspan. Positive damping effectiveness was commonly achieved from the additional longitudinal viscous dampers under the far-field ground motions when considering the wave passage effect, whereas negative damping effectiveness was observed under the near-field ground motion at certain wave velocities.

Long-span cable-stayed bridges often have a design service life of more than a hundred years, during which they may experience multiple earthquake events and accumulate seismic damage if they are located in seismic-prone regions. Earthquake occurrence is discretely and randomly distributed over the life cycle of a long-span cable-stayed bridge and often causes sudden drops in the structural performance instead of yearly fixed seismic performance degradation. This study thus proposes a digital twin-based life-cycle seismic performance assessment method for long-span cable-stayed bridges. The major components of this method include: (1) a seismic hazard analysis-based generation method of earthquake occurrence sequence; (2) a digital twin-based structural response prediction method considering lifetime earthquake occurrence and sequence; and (3) a service life quantification method. The proposed method is applied to a scaled long-span cable-stayed bridge with a series of shake table tests. The results show that the digital twin can closely reproduce the life-cycle seismic response of the bridge under sequential earthquakes. The proposed assessment method provides a more intuitive presentation of the life-cycle seismic damage accumulation process and a more accurate estimation of the service life of a long-span cable-stayed bridge.

This paper focuses on the effects of near-fault motion characteristics on the seismic performance of tall pier bridges. Using the analytical models calibrated by shake table tests, fragility analysis was conducted investigating the influence of near-fault motion features (i.e., period (T_v) and number (N) of velocity pulses). Results show that seismic fragility of the tall pier under near-fault motions is highly correlated to T_v and the damage states considered, while the influence of N is less significant. Consequently, when considering the seismic behavior of tall piers under near-fault pulse-like motions, choosing records with respect to T_v may lead to more reliable results.