The design of a footbridge is typically controlled by serviceability criteria. The dynamic forces induced by pedestrians may result in high-amplitude vibrations that the users may feel as uncomfortable, or unsafe. As a consequence of the several cases of footbridge vibration problems that occurred over the last two decades, research has been conducted to improve design criteria that account for pedestrian loading, traffic density, and comfort levels. To date, there are no accepted design guidelines in the United States to assess vibration levels in footbridges. This paper offers a general overview of the current practice for the vibration analysis of footbridges.
<p>This paper introduces a damper system developed by Thornton Tomasetti in collaboration with NASA to mitigate wind-induced vibrations in buildings. The system relies on multiple masses of water contained in separate pipes that can be tuned individually to resonate at different frequencies. Each pipe is tuned with an air spring that controls both the stiffness and damping of the water mass, allowing for substantial adjustments of the system properties after installation and throughout the lifetime of the building. In addition to being more flexible than traditional tuned-mass dampers, the proposed system can be made of low-cost components and offers a number of practical advantages, such as having a distributed mass that results in lower loads imposed on the building structure. A prototype of the system is being implemented on a 32-story residential building in New York.</p>
<p>High-rise buildings are progressively being designed and constructed in increasingly slender and complex shapes. Consequently, excessive wind-induced vibrations of these structures are a growing serviceability concern due to their flexibility. Tuned mass dampers (TMDs) are regularly incorporated into high-rise buildings for mitigating excessive wind-induced vibrations. However, traditional TMDs are only effective over a narrow domain of frequencies, require an immense mass and occupy a significant volume of interior space. A novel modular air-tuned damper system was developed which is more cost-effective and flexible in distributing its mass throughout a building to make efficient use of unused space. Importantly, the air-tuned damper system is capable of being tuned across a broad domain of frequencies to more effectively alleviate wind-induced vibrations. This paper presents a case study demonstrating the performance of a high-rise building under 1- year and 10-year wind events whilst equipped with the air-tuned damper system. Dynamic analyses were performed for evaluating the reductions of the building’s lateral accelerations considering different air-tuned damper configurations. The performance of the building under the different damper configurations is discussed.</p>
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