Seismic assessment of concrete tanks considering fluid structure interaction and nonlinear time history analysis

Seismic assessment of important existing structures what are designed according to prior seismic codes or even without considering any earthquake load is one of the most important issues for minimizing the seismic vulnerability. Within this work the seismic assessment of an existing building for radioactive waste management is presented. The investigated structure is designed as a water treatment plant consisting of six collecting tanks situated in a height of 4m and is supported by eight RC columns. The building is located in the area with the highest earthquake hazard in Austria. The main goal was to analyse the whole structure under dynamic excitation during an earthquake event and in case of overloading to give recommendations for possible retrofitting solutions. An improved method for the elaboration of precise structural models is presented, which combine dynamic in-situ measurements and FEanalysis. With dynamic in-situ tests under forced excitation by usage of a reaction mass exciter, the dynamic behaviour of the structures was determined. That followed a model updating procedure to increase the reliability of the numerical investigations. The main life loads of the building are the tanks filled with water. For consideration the fluid structure interaction (FSI) during dynamic excitation an approach with usage of adequate solid elements was implemented in the structural model. In order to assess the accuracy of the chosen approach and updated finite element model, linear spectrum analysis and time history analysis were carried out. In the parametric study, the influence of a number of parameters concerning earthquake and structural characteristics on the structural responses, especially the filling level of the collecting tanks, were investigated. For the nonlinear dynamic analysis a set of different artificial time-histories, which were generated fitting to the EC8 response, were used.