Hurricane Hazard Mitigation in Traffic Light Support Structures.

摘要

Traffic signs and signals are extensively used as vital elements in highways and urban roads for communicating with drivers, in order to convey the rules, guidance, warnings, and other highway agency information. On this basis, it is crucial to have reliable and well-maintained traffic signs and signals to ascertain that essential messages are properly conveyed to drivers in various environmental conditions. Long mast arm cantilever structures are widely used on highways all over the world. Cantilevered traffic signal support structures are slender, lightly-damped structures, and since they may have a span as long as 66 ft, they are very flexible structures, and highly sensitive to wind-induced vibrations, and their fatigue life is an important issue in the design process. Another important concern about traffic signal structures is their vulnerability in critical weather conditions, such as during hurricanes. The serviceability of these structures during hurricanes is extremely important due to their critical role in directing traffic, specifically for evacuation and rescue operation. Consequently, this study presents a methodology to suppress wind-induced vibrations in a mast arm cantilever traffic signal with a circular cylinder section, by using computational fluid dynamics (CFD) simulations to create wind load time series and a dynamic model for structural control. For wind load simulations, a time-dependent approach by implementing the Large Eddy Simulation (LES) was used. Monitoring points are defined on the mast arm to capture pressure coefficients, and then calculate distributed lift and drag forces at different sections. The simulated time histories of drag and lift forces are then used for the control purpose, after experimental validation. In order to mitigate the vibrations, distributed tuned mass dampers are investigated, making use of the available weights of the lighting boxes. The structural response with and without the dampers are simulated by a dynamic model. The dynamic analysis shows that damping enhancement in traffic lighting structures can significantly reduce vibration-induced stress, with promises to improve the safety to the traveling public, extend the life of existing traffic structures, increase traffic efficiency, and reduce the cost of new structures. Moreover, the generated wind load time histories with the dynamic model are being used for different vibration control schemes, including passive and semi-active control devices with drift magnification connections, with the objective of building a database useful for creating guidelines and recommendations on the proper use of damping enhancement devices, for future implementation in the AASHTO standard.