Research on seismic influence coefficient of seismic isolated structure with different damping ratio

The seismic influence coefficient curve of seismic isolated structure with different damping ratio, which was recommended in the Chinese code for seismic design buildings, was studied. In Chinese code, time-history analysis method is recommended for seismic isolated structure, while a simplified iteration procedure based on equivalent linear analysis is also permitted under limited conditions by using a response reduction factor to account for the variation of response as a result of damping. Subsequently, a typical 12-story reinforced concrete building isolated with lead-rubber bearings was established, and the displacement and base shear force of the isolation level were analyzed and compared by using the above two methods. The calculated results from the equivalent linear analysis are generally significantly larger than those from time-history analysis; and it can be concluded that, when the damping ratio of building structures is not equal to 0.05, the damping adjustment factor in Chinese code is too conservation. The improvement suggestions of damping adjusting and forming parameters on the seismic influence coefficient curve in Chinese code were proposed. Using the new parameters, the calculation precisions of the equivalent linear analysis can get greatly improved under different site-classes and design earthquake groups, and can be used to accurately analyze the basic dynamic response of seismic isolated building.