Design calculations indicated that the stoke lane and frankwell footbridges might often vibrate uncomfortably in normal use. To avoid this possibility, vibration absorbers were fitted to both structures. The type of vibration absorber in question is a free standing device, about the size of a small beer barrel, consisting of a sprung mass and a viscous damper. When inserted into the footbridge near to the principal antinode it raises the apparent damping considerably. Bridge response under controlled loading by a pedestrian was reduced to about a quarter in both structures. The effectiveness of the absorbers was checked regularly over a three-year period. Little change occurred at the stoke lane site but at frankwell modifications had to be made to the absorber to ensure that it stayed in full working order. Subsequently its performance has proved satisfactory. The experiences have shown that the absorber is a practical device that can be constructed and installed without a great deal of specialist knowledge using fairly simple equipment. (Author/publisher)
Abstract