Evaluation of Coefficient Method for Seismic Assessment of Existing Buildings Built on Soft Soil Sites

This paper presents the results of an ongoing investigation aimed at evaluating the Coefficient Method (CM) for the seismic assessment of existing buildings built on soft soil conditions. In the first part of this investigation, error statistics of target roof displacement demand predicted by the CM with respect to peak inelastic roof displacement demand of two frame models representative of exterior steel moment-resisting frames when subjected to 18 earthquake ground motion recorded on soft soil sites found in the San Francisco Bay Area were obtained. In the second part of this study, a statistical study of the ratio of peak inelastic displacement demand to peak elastic displacement demand (i.e. coefficient C₁) of elastoplastic single-degree-of-freedom systems when subjected to 118 soft-soil records is reported. Error statistics of coefficient C₁ were also obtained from the statistical results. A functional form that takes into account the frequency content of the ground motion is proposed to estimate coefficient C₁ when evaluating existing buildings built on soft soil sites.