Seismic response of a ten story concrete building subjected to different earthquakes

The purpose of this paper is to compare the response of a ten story concrete building in San Jose, California, under three different earthquakes. The strong-motion records of the instrumented building obtained during the 1984 Morgan Hill earthquake were used to calibrate a finite element model. Soil-structure interaction was included in the model by adding some translational springs to the foundation. The same model was subjected to 1986 Mount Lewis and 1989 Loma Prieta earthquakes. While for the first case a good match between the recorded data and analytical results was obtained, for the second one the match was not as good as expected. A modal identification analysis of the building was conducted for the three ground motions using both just output operational modal analysis (OMA) and input-output experimental modal analysis (EMA). It was demonstrated that for Loma Prieta, which presents higher amplitude shaking than the other two ground motions, the fundamental period for the transversal mode of the structure was higher than that obtained using the other two earthquakes. Consequently, the springs of the finite element model needed to be updated for Loma Prieta in order to capture the more flexible response of the building. After this adjustment, there was a good match between the recorded motions and analytical results. This study proves that the effects of soil-structure interaction becomes very important when a building is subjected to high levels of shaking. In some cases, a single model of a building with concrete shear walls may not be suitable to predict properly the behavior of the building under different ground motions.