Author(s): Kai Wei; Xiaoluo Lu
Linked Author(s):
Keywords: Foundation scour; Seismic fragility; Cable-stayed bridge; Resilience; Endurance time method
Abstract: In the recent decades, many long-span bridges are built to connect the mainland and island. Earthquake and flood scour are two common causes of failures to bridges. Earthquake damages of highway bridges have been reported and highlighted by many previous studies. More than half of the failures were caused by flood scour according to an investigation of the 500 bridge failures occurring between 1989 and 2000 in the United States. Although the earthquake and scour are usually two independent natural disasters, they can occur simultaneously for bridges located in a flood-prone and seismically active region. Therefore, it is necessary to investigate the seismic behavior of bridge structures considering scour effect. This study conducted seismic fragility analysis to investigate the influence of scour on the seismic fragility of a long-span cable-stayed bridge. Seismic fragility assessment using structural dynamic analysis is challenging for complex systems due to the high computational demand, such as the sea-crossing cable-stayed bridges. To overcome this difficulty, an efficient seismic fragility analysis framework was developed based on endurance time method (ETM). An example sea-crossing cable-stayed bridge was used as a case study to illustrate the framework for developing fragility curves. The ETM framework was validated by comparing the calculated fragility curves with those calculated by IDA framework. It is shown that the ETM is capable of significantly reducing computational effort without compromising the accuracy of fragility analysis results. The framework was then used to discuss the seismic fragility of sea-crossing cable-stayed bridges under scour and earthquakes. The influence of the time duration of endurance time acceleration functions (ETAFs) on the structural fragility was studied. Resilience is an indicator of the structural ability to withstand extreme events and restore original functionality. Considering the bridges are inevitably exposed to long-term foundation scour, the bearing capacity and material properties can deteriorate throughout the lifetime, resulting in a decrease in seismic resilience over their lifetime. A framework of seismic resilience assessment was then developed for bridges exposed to long-term scour. Three typical recovery functions were employed to establish the post-earthquake functionality recovery model considering underwater repair. The time-variant model of scour depth was developed by fitting the annual measured data with the empirical function. The model of scour depth was applied to an example bridge to assess the lifetime fragility and resilience of the bridge. It is concluded that scour can produce either beneficial or adverse effects on the component and system seismic fragilities depending on the
Year: 2024