Vibration problems in structures

Summary

Based on case studies of structures with vibration problems, experimental and theoretical investigations are carried out. The aim of the project is to develop rules for the dynamic design and retrofit of such structures.

The most important cases investigated dealt with several pedestrian bridges and a test stand for gas turbines.

Frequently, if an existing old footbridge has to be replaced, a new bridge of a similar form and appearance is requested. However, modern construction materials permit smaller cross-sections leading to a smaller stiffness and mass and hence to a higher vibration susceptibility. In the case of a bridge with a span of about 80 m and a calculated fundamental frequency of only 0.5 Hz, in the horizontal transverse direction it was not clear, if the expected vibration amplitudes would be tolerable. Therefore, a passive mass damper tuned to the dynamic properties of the bridge (fundamental frequency, estimated damping) was considered already in the planning state. In the case of a partial replacement of an historic bridge, also a tuned mass damper was studied, but finally the vibration problems could be solved by a special stiffening of the system. In the case of a footbridge with a span of about 40 m and a fundamental frequency of 2 Hz and a very small damping ratio, an efficient solution could again be developed by a tuned mass damper.

After modifying a test-stand for a fluid drive, strong vibrations occured at the waste gas wall, leading to a strong radiation of airborne noise. Based on measurements a better understanding of the real phanomena was gained and an efficient solution could be developed.

Staff

Prof. Dr. Hugo Bachmann (Guideance)
Dr. Benedikt Weber
Dr. Tadeusz Szczesiak
Dr. Glauco Feltrin

Support

ETH Zürich