Investigation of Large Coastal Bridge Performance In Hurricane Environment, CMS proposal 0301696
PI: Cai, Louisiana State University
When a hurricane strikes the coast, the results are often devastating. Even as storm prediction and tracking technologies improve, providing greater warning times, our nation is still becoming ever more susceptible to the effects of hurricanes due to the massive population growth in the south and southeast along the hurricane coast from Texas to Florida to the Carolinas. As backbones of transportation lines, coastal bridges are extremely important in supporting evacuations. In addition to the general wind- induced problems, long-span large coastal bridges on hurricane evacuation routes face the threats from the combination of hurricane-induced winds, heavy traffic, and their interactions. The objectives of the proposed study are: (1) to study the performance of large coastal bridges under the action of strong winds as well as heavy traffic. This situation happens in a scenario of hurricane evacuation; (2) to investigate the effect of temporary mass dampers in ensuring bridge safety and/or reducing bridge vibration. The temporary mass dampers can conveniently be driven on the bridge when needed and be removed otherwise; and (3) to advance the state-of-the-art of aerodynamic analysis of large bridges under strong winds.
In a typical aerodynamic analysis of long-span bridges, no traffic load is considered by assuming that bridges will be closed to traffic at high wind speeds. Therefore, bridges have been tested in the wind tunnel or analyzed numerically based on the pure bridge section without vehicles on it. However, during a hurricane evacuation, the bridges may be occupied by slowly moving traffic. On one hand, vehicles affect the modal characteristics and section shape of the bridge, which affects the aerodynamic behavior. On the other hand, the same vehicles may act like mass dampers that may help damp out some vibrations. The total effects of the traffic on bridge performance and also bridge vibrations on vehicles are not clear and no studies have been reported. While it is generally assumed (but still controversial) that turbulence helps enhance bridge flutter velocity, the effects of hurricane-induced high turbulence on bridge stability haven't been adequately studied. These issues need to be addressed to ensure the safety of both bridge and vehicles during hurricanes and evacuations. While the developed procedures are intended for general coastal bridges, the Luling Bridge near New Orleans will be used as the primary subject of study. Both wind tunnel testing and numerical simulations will be conducted. The bridge performance will be investigated by arranging different traffic patterns to find the worst case for safety assurance, and find the optimal pattern that may be utilized for hazard mitigation (e.g., closing certain lanes). Another alternative is to develop a movable TMD system that can be driven on the bridges to act as a temporary vibration damper. The research activities and results will be incorporated into the new education curriculum - Hurricane Engineering developed at LSU with the NSF fund.
The proposed study is to address the issue of how large coastal bridges perform in hurricanes under evacuation conditions. The answer is very important since thousands of lives potentially hinge on the decision of when to close the evacuation routes too soon and people may be trapped in coastal areas subject to storm surge, too late and people may be on the bridge under unsafe conditions. The educational activities include high school outreaching, minority students recruiting, and technical information dissemination. These activities will promote minority participation, affect high school students career path, and foster future engineers to develop more systematical strategies in dealing with the most destructive hurricane hazards for years to come. International collaboration with Tongji University, China, will not only utilize the second largest boundary layer wind tunnel facility in the world, but will also foster further research and collaboration, increase the visibility of hurricane engineering in both countries, and combine the resources to deal with the worldwide engineering challenge of the 21st century . mitigating hurricane hazards. To achieve the research objectives, a unique team of researchers is formed. This team consists of Dr. Cai (PI) who has extensive expertise in wind vibration analyses, Dr. Levitan (co-PI), director of the LSU Hurricane Center and an expert in wind loading, Dr. Nikitopoulos (co-PI) is the Director of Wind Tunnel Laboratory with expertise in fluid dynamics and wind tunnel simulation.
