Flood Disaster Resilient Bridge Structures For Sustainable Bridge Management Systems

Abstract

Extreme weather events are occurring at an increasing ferocity and frequency. Floods are the most comand damaging natural disaster. More than 4,400 occurrences of flood disasters have been reported globally between 1900 and 2016. As a result, around seven million people were killed and millions more were displaced. Climate impacts are expected to intensify weather related flooding events, and sea level rise expected worldwide will increase the risk of coastal disasters. Transportation infrastructure, vital to the economy and society of every country, is especially prone to the inland and coastal floods. Bridge structures are under the constant threat of these natural disasters. Superstructures can be washed away due to lateral forces generated by floodwater. Floodwater can also accelerate scouring around bridge piers, which often contributes to bridge failures. This research used the results of an extreme flood simulation conducted by the Center for Advanced Infrastructure Technology at the University of Mississippi. A flood inundation model was implemented for an extreme flood scenario at a floodplain site of Little Tallahatchie River in Northern Mississippi that featured surface transportation corridor sites and other infrastructure assets. Geospatial analysis of flood inundation mapping and simulation results shothat total flood inundation covered an area of 22.46 sq mi2 (58.16 sq km2) in the floodplain, where maximum floodwater depth reached up to 34.19 ft (10.42 m) within the inundation area. The results of the extreme flood simulation were used for assessing structural integrity of a bridge structure subject to lateral floodwater forces, with primary focus on the superstructure. A Three Dimensional-Finite Element model of US-51 Highway bridge, located in the floodplain site, was developed for flood impact analysis considering bridge girder-deck superstructure, bearings, pile caps and piers. The numerical results of finite element simulation shothat the bridge superstructure displaced 2.42 m under the lateral hydrodynamic force of floodwater. The dowel bars inserted at the bottom of each girder end through bearing to the top end of pile cap, failed in shear against lateral floodwater forces. This would lead to the failure of US-51 Highway bridge superstructure if an extreme flood event occurs in real life. A framework for structural integrity assessment of bridge structures is presented with Flood Resiliency Index. Recommendations for design enhancements and hardening of bridges are discussed for flood disaster resilience. An enhanced geospatial decision support system is recommended considering “vertical underclearance” criteria for bridge superstructure height above the channel and “flood probability” related to flood occurrence in 10, 50, 100, 500 and 1,000 years. These flood resilience parameters are missing from the traditional bridge management system (BMS) framework. Enhancing the current practice of BMS is proposed using optimization based prioritization of flood disaster vulnerable bridges, which considers vertical underclearance criteria, flood disaster risk probability and life cycle cost analysis. For this purpose, a Flood Vulnerability Rating (FVR) is proposed on a scale of 1 (catastrophic risk) to 6 (very low risk). The FVR scale was used for a case study of 270 bridges on major rivers in the state of Mississippi, which were analyzed using an optimization objective function to maximize benefits considering reconstruction/hardening costs and indirect benefits (cost avoidance from traffic disruption and economic loss related to bridge failure). Based on the present-worth life cycle analysis, total life cycle costs for the agency’s pre-planned bridge hardening for flood resilience was 59.3% less than the case of no hardening of the same bridge. This dissertation advances flood risk assessment and resilience management methodologies for transportation infrastructure in the United States and across the globe