RESPONSE OF A 42-STORY STEEL-FRAME BUILDING TO THE M(S)=7.1 LOMA-PRIETA EARTHQUAKE

A set of 14 acceleration records was obtained from a 42-storey steel-f rame building, the Chevron Building, in San Francisco during the M(s) = 7.1 Loma Prieta earthquake of 17 October 1 989. Data were analysed u sing a system identification method based on the discrete-time linear filtering, and the least-squares estimation techniques. The results sh ow that the response of the building is dominated by two modes: a tran slational mode in the weaker (southwest-northeast) principal direction of the building at 0.1 6 Hz with 5% damping, and a translational-tors ional mode along the east-west diagonal of the building's cross-sectio n at 0.20 Hz with 7% damping. There are significant contributions from higher modes at 0.54 Hz, 0.62 Hz, 1.02 Hz and 1.09 Hz. All the modes incorporate some torsion, but the amplitudes of torsional components a re small, about 10% of translational amplitudes. Soil-structure intera ction influences the vibrations near 1.0 Hz. The contribution of soil- structure interaction to the peak displacements of the building is sig nificant, particularly at lower floors.