Model-based TMD Design for the Footbridge "Inwilerstrasse" in Switzerland and ist Experimental Verification

The TMD system of the footbridge "Inwilerstrasse" near Zug in Switzerland was model-based designed for the first vertical bending mode, the expected human excitation, assuming the inherent damping of 0.3 % and ensuring the acceleration limit CL1 (0.50 m/s²) of HIVOSS. After the installation of the locked TMDs, first, the TMD frequency was optimized based on the identified bridge eigenfrequency by adjusting the TMD mass.

Then, the bridge with locked and activated TMDs was excited by five synchronized persons. These tests were re-computed adopting the experimentally identified eigenfrequency and damping ratio of the first bending mode and the optimized TMD mass. The re-computation demonstrates that the excitation force amplitude of one bouncing person must be set to approximately 600 N in order to obtain the measured acceleration of 0.117 m/s² of the bridge with activated TMDs. The value of 600 N seems reasonable as this corresponds to approximately 80 % of the average body weight (76 kg) of one person. The very low acceleration of 0.117 m/s² of the bridge with activated TMD demonstrates the effectiveness of TMDs.

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