VIBRATION UPGRADING OF GYMNASIA, DANCE HALLS AND FOOTBRIDGES

Rhythmical human body motions can cause strong vibrations of structures. Possible remedial measures are frequency tuning, limiting amplitudes and use of tuned mass dampers. Case studies of vibration upgrading of gymnasia, dance halls and two footbridges illustrate the practical use of the fundamental principles. A reinforced concrete footbridge with a hollow box section and a width of about 4 m was designed as a continuous beam with six sections of regular span lengths of 15.5 m, and the bridge was supported by roughly 7 m high single columns with a cross-section of 65 x 30 cm. Dynamic tests were performed by the Swiss Federal Institute of Technology at Lausanne after unacceptable horizontal vibrations occurred in both the transverse and the longitudinal directions. As a result the bridge was upgraded and the horizontal frequency increased by strengthening the foundation slab and the columns. The second bridge, a 2.5 m wide steel footbridge and cyclist bridge designed as a continuous beam with 4 spans, exhibited strong vibrations under walking and running motions and was found to have a fundamental frequency of 2.46 Hz without any substantial live load. This bridge was upgraded by installing two tuned mass dampers in the middle of the 2.5 m span.