Wind and gusts from passing trucks create vibration in traffic signal mast arms, putting stress on the structures. Over time, repeated stresses can cause a structure to fatigue and eventually fail. Aside from obvious safety and liability concerns, vibrations can also impact the quality of video imagery used for surveillance and vehicle detection. (here’s a video of this happening:
Vibrations may be reduced by increasing the size of the structure and, consequently, the structure foundation but this comes at a price. The cost of larger structures is higher and space at the corners of intersections is a precious resource, particularly in urban environments. Large mast arm foundations consume real estate that could be used to provide handicapped-accessible sidewalk width, sidewalk ramps or other streetscape amenities.
Another option to reduce vibration is to install a vibration damper. UConn’s own Professor Richard Christenson, Ph.D., of the Civil and Environmental Engineering Department, conducted research into a solution which reduces the amplitude and duration of vibrations using magnetic and pneumatic dampening. This type of vibration damper, which may be installed on new mast arms or retrofitted onto existing structures to increase their life span, weighs approximately 35 lbs. The device is less than four feet long and approximately 4.5 inches in diameter and is installed on the mast arm. With a vibration damper, the weight of the required structure may be reduced by 25 to 40 percent.
Hartford, Connecticut was one of the first cities in the country to use dampers of this type as a solution to a construction issue. A mast arm foundation was mistakenly poured with a 24” bolt circle instead of the specified 30” bolt circle. The vibration damper allowed the use of a smaller mast arm structure compatible with the 24” bolt circle.