Traffic Excited Vibrations Acting on Pedestrians Using a Highway Bridge

Abstract

The new Langensand Bridge Lucerne is a single span bridge with a span length of 80 m and a width of 27 m. Whereas the middle part of the bridge is used by five road traffic lanes, pedestrian and cyclist lanes are located on both cantilevers. These have a free span length of about 6 m each. The questions to be answered through the experimental investigation discussed here were: Are the pedestrians walking on the bridge cantilevers annoyed by traffic induced vibrations? If yes, what would be the optimum layout for TMD’s (tuned mass dampers)? In a first step, an ambient vibration test was performed. The structure’s natural vibrations were extracted from vibrations predominantly excited by the many trains passing on the 11 railway tracks underneath the bridge. The measurement point grid consisted of 52 points. In the 1...34 Hz range, 21 natural modes of the bridge could be identified. In a second step, 77 dynamic tests were performed with three heavy vehicles (equipped with steel and air suspensions respectively) being driven over the bridge in different configurations. Maximum acceleration amplitudes measured at the free cantilever end were in the range of a = 0.5...0.8 m/s2 for passages on the normal pavement and reached about a = 2.6 m/s2 for passages over a 25 mm and a 50 mm plank respectively, located at midspan. These values were rated as acceptable. No attempts had to be taken to design a TMD system.