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<p>The seismic vulnerability of highway bridges in Nepal has received limited attention despite the country’s high seismic risk. Bridges along the Kathmandu Terai Fast Track (KTFT), a strategic expressway corridor, traverse complex geological formations, including Siwalik and Quaternary deposits, and are exposed to near-fault effects as they closely traverse and directly intersect the Main Frontal Thrust (MFT) and Main Boundary Thrust (MBT). Limited research has been conducted on how site-specific near-fault effects and complex geological conditions influence conventional PSHA-based bridge fragility assessments in Nepal. This study evaluates the impact of PSHA-based, near-fault, and site-response-modified ground motions (GMs) on the fragility of a seismically isolated RC box girder bridge using nonlinear finite element modeling. System-level and component-level fragility curves for bridge piers and lead rubber bearings (LRBs) are developed through Incremental Dynamic Analysis (IDA). Results indicate that the bridge is most vulnerable under near-fault GMs, where fragility estimates exceed those from PSHA-based and site-response-modified GMs. LRBs exhibit significantly higher fragility than bridge piers, reaching extensive and collapse damage states at lower intensities, particularly under near-fault excitations where displacement demands surpass design expectations. System-level fragility confirms that bridge failure is primarily governed by LRB fragility, highlighting that seismic isolation effectiveness depends strongly on ground motion characteristics. The study findings demonstrate that site-response analysis improves fragility estimations over empirical PSHA-based approaches, but near-fault effects introduce additional challenges. Seismic isolation design &amp; maintenance must explicitly account for near-fault scenario, and fragility assessments should integrate detailed site-response analysis for improved accuracy in Nepal’s seismic bridge design provisions. These findings emphasize that seismic isolation design and maintenance must explicitly account for near-fault scenarios, particularly considering LRB displacement sensitivity under strong ground motions. Additionally, fragility assessments should integrate detailed site-response analysis and ground motion scaling sensitivity studies to enhance the accuracy of seismic bridge design provisions in Nepal.</p>

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Seismic Fragility Assessment of Seismically Isolated Multi Span Continuous Box Girder Bridge in Nepal Considering Local Site Effects

  • 期刊论文

  • 发表日期：

    2025年3月20日

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  • Sushant Giri,
  • Tushar Bansal

摘要

The seismic vulnerability of highway bridges in Nepal has received limited attention despite the country’s high seismic risk. Bridges along the Kathmandu Terai Fast Track (KTFT), a strategic expressway corridor, traverse complex geological formations, including Siwalik and Quaternary deposits, and are exposed to near-fault effects as they closely traverse and directly intersect the Main Frontal Thrust (MFT) and Main Boundary Thrust (MBT). Limited research has been conducted on how site-specific near-fault effects and complex geological conditions influence conventional PSHA-based bridge fragility assessments in Nepal. This study evaluates the impact of PSHA-based, near-fault, and site-response-modified ground motions (GMs) on the fragility of a seismically isolated RC box girder bridge using nonlinear finite element modeling. System-level and component-level fragility curves for bridge piers and lead rubber bearings (LRBs) are developed through Incremental Dynamic Analysis (IDA). Results indicate that the bridge is most vulnerable under near-fault GMs, where fragility estimates exceed those from PSHA-based and site-response-modified GMs. LRBs exhibit significantly higher fragility than bridge piers, reaching extensive and collapse damage states at lower intensities, particularly under near-fault excitations where displacement demands surpass design expectations. System-level fragility confirms that bridge failure is primarily governed by LRB fragility, highlighting that seismic isolation effectiveness depends strongly on ground motion characteristics. The study findings demonstrate that site-response analysis improves fragility estimations over empirical PSHA-based approaches, but near-fault effects introduce additional challenges. Seismic isolation design & maintenance must explicitly account for near-fault scenario, and fragility assessments should integrate detailed site-response analysis for improved accuracy in Nepal’s seismic bridge design provisions. These findings emphasize that seismic isolation design and maintenance must explicitly account for near-fault scenarios, particularly considering LRB displacement sensitivity under strong ground motions. Additionally, fragility assessments should integrate detailed site-response analysis and ground motion scaling sensitivity studies to enhance the accuracy of seismic bridge design provisions in Nepal.