Date of Award
1-1-2025
Document Type
Dissertation
Degree Name
Ph.D. in Engineering Science
First Advisor
Jacob J. Najjar
Second Advisor
Christopher C. Mullen
Third Advisor
Amir A. Mehrara Molan
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Natural disasters such as floods and earthquakes pose significant threats to the resilience of highway transportation systems, particularly compromising the safety and serviceability of bridges. In regions susceptible to both seismic activity and flooding, the combined effects of earthquake loading, flood-induced scour, and hydrodynamic forces create a critical multi-hazard scenario. This research develops a comprehensive multi-hazard analysis framework to evaluate bridge performance under combined seismic and flood-induced hazards. Three-dimensional finite element (FE) models of representative three- and six-span steel girder bridges are developed and analyzed under varying scour depths and hydrodynamic loading conditions. Modal analysis, static pushover analysis, and non-linear time history analysis are conducted using ground motions representative of catastrophic events in the New Madrid Seismic Zone (NMSZ). The multi-hazard analysis methodology is also applied to a real 11-span bridge in northern Mississippi to assess its performance under region-specific flood and earthquake scenarios.
This study investigates the seismic vulnerability of bridges under the combined effects of earthquake loading, flood-induced scour, and hydrodynamic effects. The analysis reveals that scour significantly affects the fundamental periods, stiffness, displacement ductility, and structural capacity of the bridges. Under combined hazard conditions, moment demands, lateral displacements, and foundation vulnerabilities increase, with shallow scour depths that substantially compromise foundation stability during seismic events. The hydrodynamic effects become critical at deeper scour depths, at which the moment demand increases by up to 25%. These results highlight the importance of accounting for hydrodynamic forces in seismic risk assessments, particularly for bridges exposed to deeply scoured foundations and high-water regions. Fragility curves are developed for a real bridge, using displacement ductility as the engineering demand parameter for varying scour conditions. The results indicate that the scour substantially affects the seismic fragility of the bridge. As the depth of the scour increases, the probability of exceeding all damage states increases significantly, highlighting the critical need to consider the effects of the scour in seismic risk assessments for bridges in flood- and earthquake-prone regions. The multi-hazard framework in this study provides a practical analysis framework for evaluating bridge vulnerability under combined earthquake and flood scenarios, thereby contributing to the design and maintenance of more resilient bridge infrastructure. These findings emphasize the importance of implementing scour countermeasures and incorporating multi-hazard considerations into bridge design and maintenance strategies.
Recommended Citation
Gautam, Raul, "Multi-Hazard Analysis of Bridges Under Seismic, Flood-Induced Scour, and Hydrodynamic Loading" (2025). Electronic Theses and Dissertations. 3281.
https://egrove.olemiss.edu/etd/3281