Abstract
Costal bridge systems usually contain tall piers with heights over 40 m, due to the engineering site exposed to deep water circumstances. Note that the conventional seismic isolation devices (e.g., isolation bearings) are not that effective for tall piers, since their dynamic performance is significantly affected by the distributed mass and vibration modes of columns; therefore, base isolation design philosophy could be a promising alternative for mitigating seismic demands of this type of bridges. This paper mainly investigates the efficiency of rocking foundations in improving seismic performance of tall pier bridges, with the results presented in the format of fragility curves. Finite element model of the prototype tall pier bridge is developed, and the responses subjected to near-fault motions are obtained using nonlinear time history analysis. Probability seismic demand models and fragility curves are then developed accordingly, based on which the performance of tall pier bridges are assessed. The results show that employment of rocking foundations could significantly reduce the demands of tall piers and the probability of being damaged. Before the initiation of uplifting at pier base, the behavior of rocking piers resembles that of conventional ones with integrated foundation. While rocking initiates under strong excitations, the demands of rocking piers reduce drastically compared with integrated ones and tend to be similar under different motions, which benefits the post-earthquake performance assessment of these bridges.
Highlights
Numerous coastal highway bridges have been constructed in recent decades, among which tall piers could be widely observed since the engineering sites are usually exposed to deep water circumstances (Liu et al 2007; Deng et al 2017)
Current investigations showed that the seismic performance of tall piers is significantly affected by the distributed masses and vibration modes of columns, which differed from conventional short-to-medium piers Chen et al (2016, 2018b, (2019; Chen and Guan (2020), 2018a, 2018b) pointed out that due to the higher-order modes, the seismic shear force and bending moment demands of tall piers could several times greater than those computed with capacity-protect method employed in current codes
Current study concentrates on the seismic performance tall piers employing rocking foundations, with the results presented in the format of fragility curves
Summary
Numerous coastal highway bridges have been constructed in recent decades, among which tall piers could be widely observed since the engineering sites are usually exposed to deep water circumstances (Liu et al 2007; Deng et al 2017). For conventional bridges with short-to-medium piers, one of the most commonly employed seismic isolation design strategy is to implement isolation bearings between girders and piers (Jangid 2007; Chen et al 2009; Kelly and Konstantinidis 2011), including lead rubber bearings (LRB), friction pendulum bearings (FPB), and high-damping rubber bearings (HDRB). These bearings protect the piers through mitigating the lateral inertial force transmitted from the superstructures, as well as increasing the structural damping vibration periods (Yamamoto et al 2012). Probability seismic demand models (PSDMs) and fragility curves are developed based on which the performance of tall pier bridges are assessed
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