Floor Acceleration Demand on Steel Moment Resisting Frame Buildings Retrofitted with Linear and Nonlinear Viscous Dampers

An improvement of the seismic performance of a building can be achieved by adding supplemental damping through viscous dampers. In some cases, however, the incorporation of viscous dampers in the structure can cause an increment of the seismic demand on acceleration-sensitive nonstructural elements. Two steel moment resisting frame buildings of three and six stories were selected from the SAC Steel Project in California. These buildings were equipped with linear and nonlinear viscous dampers designed by following a uniform distribution design approach in which a unique damping coefficient is assigned to all dampers along the building’s height. Additionally, three target first modal damping ratios were used along with six different velocity coefficients of the fluid viscous dampers. Nonlinear time-history analysis was carried out with the FEMA P695 far-field ground motion record set. The records were scaled to two intensity levels and floor acceleration time histories and 5% damped floor acceleration response spectra were obtained. The results show that the implementation of viscous dampers generally reduces the seismic demand in terms of floor acceleration compared to the original (nonretrofitted) building in most cases. Nevertheless, the floor acceleration demand varies significantly when the damping ratio and the velocity coefficient of fluid viscous dampers are varied. In some cases, the peak floor accelerations and the floor spectral accelerations in certain non-structural period ranges can exceed that of the original building.