Seismic Response of a Large-Span Steel Truss Arch Bridge under Nonuniform Near-Fault Ground Motions

The ground motion in the near-fault region of an earthquake is characterized by exceptional energy levels, powerful velocity impulses, substantial spatial variability, and notable permanent displacement. These unique attributes can dramatically escalate structural damage. Steel truss arch bridges, being critical components of transportation networks, are particularly vulnerable to these phenomena due to their extensive stiffness spans. Such factors are difficult to accurately simulate. In this study, real near-fault ground motions that incorporate spatial variability effects and pulse effects are used to excite the long-span arch bridge, thereby striving to realistically reproduce the structural damage sustained by the bridge under the simultaneous influence of near-fault spatial variability and pulse effects. This study adopts an arch bridge with a span closely approximating the spacing between stations (200 m) of the SMART seismic array as a case study. The near-fault ground motions, characterized by spatial variability and captured by the array, are selected as seismic samples, while the far-field ground motions recorded by the same array serve as a comparative reference. The seismic excitations are then input into the bridge case study, following the spatial correspondence of the stations, using a large-scale finite element program to obtain the structural response. Upon analyzing the seismic response of crucial positions on the bridge, it became evident that the arch foot of the bridge is more susceptible to the spatial variability in near-fault ground motion, whereas the vault experiences a greater impact from the high-energy velocity pulse. Specifically, under nonuniform seismic conditions, the internal force at the base of the bridge arch increased significantly, averaging a rise of 18.69% compared to uniform excitation conditions. Conversely, the displacement and internal force response at the top of the arch exhibited more modest increases of 6.48% and 10.33%, respectively. Under nonuniform excitation, the vault’s response to near-fault earthquakes increased by an average of 20.35% com-pared to far-field earthquakes, while the arch foot’s response rose by 11.55%. In contrast, under uniform excitation, the vault’s response to near-fault earthquakes was notably higher, increasing by 25.04%, while the arch foot’s response showed a minor increase of only 2.28%. The study has revealed significant differences in the sensitivity of different parts of long-span arch bridges to near-fault earthquake characteristics. This finding is of great importance for understanding the behavior of long-span arch bridges under complex earthquake conditions. Specifically, the arch foot of the bridge is more sensitive to the spatial variability of near-fault ground motions, while the arch crown is more significantly affected by high-energy velocity pulses, providing new insights for bridge seismic design. Furthermore, the differences in response between the arch crown and arch foot under different earthquake excitations also reveal the complexity and diversity of bridge structural responses.

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