Increasing Fatigue Life of Cantilevered Traffic Signal Support Structures using an Innovative Vibration Absorber.

摘要

Traffic signal support structures are flexible, lightly-damped structures that are highly susceptible to wind-induced vibration. The sustained large amplitude deflections due to these dynamic vibrations can result in fatigue cracking and failure. An innovative vibration absorber is proposed to reduce fatigue in traffic signal support structures using the mass of the signal head as a damped vibration absorber. This novel concept, referred to as a signal head vibration absorber (SHVA), provides energy absorption to the lightly damped signal support structure in the form of increased damping. A prototype smart vibration absorber, envisioned as an inexpensive retrofit to traffic support structures experiencing excessive wind-induced vibration, is tested in a full-scale laboratory experiment at the University of Connecticut. An optimally tuned SHVA is experimentally shown to increase the damping in the traffic support structure from 0.2% of critical to 10.1%. For steady state vibration this is equivalent to a 98.3% reduction in the response, virtually eliminating any deflections. Individual optimal tuning is a drawback for use of this device in the field where the natural frequency of the typical cantilevered signal support structures vary in the range of 0.7 Hz to 1.4 Hz But the relatively large additional mass of the signal head provides the flexibility to use one tuned SHVA for a wider range of frequency. It is shown that a single SHVA can be applied to a wide range of signal support structures while still achieving reasonable performance. Testing on two full scale cantilevered support structures show that even for 43% mistuning the SHVA increases the damping from 0.1% critical to 1.8% critical and reduces the tip acceleration from 0.093g to 0.057g in 13 seconds. An analytical study shows when a single SHVA is used to mitigate the vibration of multiple signal support structures, the SHVA should be optimally tuned to the natural frequency of the lowest frequency, and typically longer and heavier, signal support structure. The SHVA can potentially change the way vibration in traffic signal support structures is mitigated.