Summary
This paper presents results of one‐g shake‐table tests on scoured pile‐group‐supported bridge models in saturated (liquefiable) and dry (nonliquefiable) sands. The primary objective is to reveal the influence of liquefaction on seismic demands and failure mechanism of scoured bridges. To this end, two identical models, each consisting of a 2 × 2 reinforced concrete pile‐group with a center‐to‐center spacing of 3 times pile diameter, a cap and a single pier with a lumped iron block, were constructed and embedded into saturated and dry sands, respectively, with the same scour depth of 4 times pile diameter. Typical test results, including excess pore pressure, acceleration and displacement demands are interpreted first, followed by the focus on curvature demands and associated seismic failure mechanism identification. Finally, inertial and kinematic effects on pile curvature demands are estimated using cross‐correlation analyses. Results show that near‐pile liquefied soils exhibit more remarkable dilation tendency as compared to far field. For bridges under the given scour depth, soil liquefaction tends to significantly affect the failure modes via transferring damage positions from pier bottom to pile head and meanwhile from underground pile to pile head. In addition, pile group effects appear to be significant in nonliquefiable soils while to be relatively inessential in liquefied soils. Moreover, the inertial effect is more prominent in nonliquefiable soils, while the kinematic effect itself generally appears to be more significant in liquefiable soils. The test results can be used to validate numerical models for future studies.
Scour can be a potential risk to bridge’s safety during the service life. Generally, the scour can increase the unsupported pile length of bridge and change the dynamic characteristics of the substructure. Consequently, this can decrease the lateral load capacity of the bridge, especially to pile-supported bridges. In this article, the dynamic interaction between bridge pier and its foundation considering earthquake and scour depths was investigated based on a simplified 2-degree-of-freedom model. The results demonstrated that there is a significant resonance between the pier and the pile foundation due to the contribution of large pile cap mass. Additionally, the effect of scour depths is strongly related to the fundamental vibration periods of both the superstructure–pier system and the pile foundation itself. Moreover, an approximate most adverse equivalent pile length considering the scour depth was formulated and proposed to efficiently and easily capture the worst seismic responses of the bridge pier. The accuracy of the methodology proposed herein was verified by an existing three-span continuous girder bridge in China.
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