Seismic upgrading of existing structures

Summary

Approximately 95 % of the existing structures in Switzerland were not designed for seismic action or based on obsolete rules. These structures are in general very vulnerable and possess an unknown, often inadequate, seismic safety. Even in the case of a moderate earthquake, human casualties and severe damage have to be expected, especially damage to the environment caused by chemical plants. Efficient methods and measures have to be developed to improve the seismic performance of existing vulnerable structures.

Of great importance is the dynamic behaviour of structures with respect to site and soil specific design spectra. Possible upgrading methods are structural weakening, strengthening or improving local and global ductility.

In the report period liquid gas tanks representing an important threat to the environment have been evaluated. Instead of strengthening or increasing the ductility, it was found that base isolation was the most efficient upgrading method. Installing high damping rubber bearings shifted the eigenfrequency to a lower spectral range and drastically reduced the seismic action. On the other hand, the seismic safety of the existing structure was greatly increased. The seismic behaviour of the upgraded structure was verified by a nonlinear time domain analysis considering the actual material law of the rubber bearings.

Staff

Prof. Dr. Hugo Bachmann (Guideance)
Dr. Thomas Wenk