Investigation of Large Coastal Bridge Performance in Hurricane Environment

飓风环境下大型海岸桥梁性能的调查，CMS提案0301696PI: Cai，路易斯安那州立大学当飓风袭击海岸时，结果往往是毁灭性的。即使风暴预测和跟踪技术不断进步，提供了更准确的预警时间，我们的国家仍然变得越来越容易受到飓风的影响，因为从德克萨斯州到佛罗里达州再到卡罗来纳州，沿飓风海岸的南部和东南部人口大量增长。沿海桥梁作为交通干线的骨干，在支援疏散方面发挥着极其重要的作用。除了一般的风引起的问题外，飓风疏散路线上的大跨度大型沿海桥梁还面临着飓风引起的风、繁忙的交通及其相互作用的威胁。本研究的目的是：(1)研究大型沿海桥梁在强风和繁忙交通作用下的性能。这种情况发生在飓风疏散的场景中；(2)研究临时质量阻尼器在保证桥梁安全和/或减少桥梁振动方面的作用。临时质量阻尼器可以方便地在需要时驱动到桥上，否则可以拆卸；(3)推动了大型桥梁在强风作用下气动分析的研究进展。在典型的大跨度桥梁气动分析中，假设桥梁在高风速下将关闭，不考虑交通荷载。因此，在风洞中对桥梁进行了测试，或根据不含车辆的纯桥梁截面进行了数值分析。然而，在飓风疏散期间，桥梁可能会被缓慢移动的车辆占用。车辆对桥梁的模态特性和截面形状产生影响，从而影响桥梁的气动性能。另一方面，同样的车辆可能会起到质量减震器的作用，可以帮助消除一些振动。交通对桥梁性能的总体影响以及桥梁振动对车辆的影响尚不清楚，也没有研究报告。虽然人们普遍认为（但仍有争议）湍流有助于增强桥梁颤振速度，但飓风引起的高湍流对桥梁稳定性的影响尚未得到充分研究。这些问题需要解决，以确保在飓风和疏散期间桥梁和车辆的安全。虽然所制定的程序适用于一般的沿海桥梁，但新奥尔良附近的芦陵大桥将作为主要研究对象。将进行风洞试验和数值模拟。通过安排不同的交通模式来调查桥梁的性能，以找到安全保证的最坏情况，并找到可能用于减轻危害的最佳模式（例如，关闭某些车道）。另一种替代方案是开发一种可移动的TMD系统，该系统可以在桥梁上驱动，作为临时减振器。研究活动和结果将被纳入路易斯安那州立大学在国家科学基金会资助下开发的新教育课程——飓风工程。拟议的研究是为了解决大型沿海桥梁在飓风疏散条件下的性能问题。答案是非常重要的，因为成千上万的生命可能取决于何时关闭疏散路线的决定，太早的话，人们可能会被困在受风暴潮影响的沿海地区，太晚的话，人们可能会在不安全的情况下在桥上。教育活动包括高中外展、少数民族招生和技术信息传播。这些活动将促进少数民族的参与，影响高中学生的职业道路，并培养未来的工程师在未来几年里制定更系统的策略来应对最具破坏性的飓风灾害。与中国同济大学的国际合作不仅将利用世界第二大边界层风洞设施，还将促进进一步的研究和合作，提高两国飓风工程的知名度，并结合资源应对21世纪的全球工程挑战。减轻飓风危害。为了实现研究目标，形成了一个独特的研究团队。该团队由具有丰富的风振分析专业知识的Cai博士（PI）， LSU飓风中心主任和风荷载专家Levitan博士（PI），风洞实验室主任Nikitopoulos博士（PI）（流体动力学和风洞模拟专业知识）组成。

Investigation of Large Coastal Bridge Performance In HurricaneEnvironment, CMS proposal 0301696PI: Cai, Louisiana State UniversityWhen 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.