Long term seismic response monitoring and finite element modeling of a concrete building considering soil flexibility and non-structural components

This paper presents a study of the variation of natural frequencies and damping ratios of a reinforced concrete building identified from earthquake records during a period of four years. The three storey reinforced concrete building is instrumented with five tri-axial accelerometers. The state-space subspace system identification technique was used to ascertain the natural frequencies and damping ratios considering 50 recorded earthquake response time histories. Correlations were developed between the peak ground acceleration at the base level and peak response acceleration at roof level with identified frequencies and damping ratios. It was found that modal characteristics of the building are sensitive to the level of excitation and response. A general trend of decreasing fundamental frequencies and increasing damping ratios with increased level of shaking was observed. A three dimensional finite element model of the building was developed to study the influences of soil and various structural and non-structural components. To incorporate real in-situ conditions, soil underneath the foundation was modeled using spring elements and non-structural components (cladding, in-fills and partitions) were also included. It was concluded from the investigation that participation of soil and non-structural components towards the seismic response of the building is significant and these should be considered in models to simulate the real behavior.