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Abstract
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Despite the massive population growth in the south and southeast along the hurricane coast of the United States, the transportation infrastructure has not increased its capacity accordingly. Long-span bridges are usually the backbones of transportation lines along the coastal areas. When a hurricane is approaching, these long-span bridges sometimes have to be closed in order to ensure the safety of the bridge as well as the transportation on them due to excessive wind-induced vibrations, which however greatly reduces the capability of hurricane evacuation through the bridges.
To date, bridge vibration controls in high wind speeds have not been adequately addressed. Most previous control work dealt with the bridge buffeting under moderate wind speeds, along with some cases of flutter controls in high wind speeds. While active control devices may provide satisfactory multi-objective control performance in a full range of wind speeds, their dependence on external energy supply has hindered their applications to the disaster evacuations. Recently, some aerodynamic controls using flaps were proposed to control flutter instability. However, their applicability to buffeting control has not been reported and established.
Vehicles on bridges act as a sort of Spring-Damper-Subsystems (SDSs) to the bridge. The SDS is used here as a general terminology to differentiate with Tuned Mass Dampers (TMDs). The former may or may not be pre-tuned, while the latter is pre-tuned to the "optimal" value (usually the fundamental frequency of the structural system) for efficient vibration control. The objective of the present study is to investigate the effects of different SDSs (with different vibration frequencies) on the bridge performance during hurricane evacuations and develop a truck-type of movable passive SDS. The passive nature makes the control approach more reliable than the active one, considering the reality that power may not be available during the hurricane disasters. The temporary/movable SDS can be conveniently driven on the existing bridges when necessary, and be removed when it is not needed.
It has been reported that the gust wind speed during hurricanes could be up to 60-80 m/s or more in the United States and other areas. Though the duration may be short, the consequence of such strong winds may be catastrophic for both the safety of the bridge and the safety of traffic on the bridge. |