Performance based design (PBD) and a system of steel special moment resisting frames with viscous damping devices were used for the seismic design of two new multi-story midrise buildings in California. The first structure is located in Los Angeles Basin, in a region of high seismicity. The second building, which is located in Central Valley, a region of moderate seismicity, is one of the first structures in the United States to apply 2005 ASCE 7-05 procedure to design In accordance with ASCE 7-05, the steel frames were sized and designed with strength requirements of the static force level force. Dampers were provided to control displacement of the structures. Earthquake performance and cost effectiveness were the primary concerns in designing the buildings. However, long-term performance was also assessed. Comparative analyses of the PBD and conventional design (CD) buildings showed that the PBD building had superior seismic performance. PBD approach lead to a longer period structure reducing seismic demand and floor accelerations. Dampers reduced the story drift ratios below the design limits. A cost study shows that much of the damper expense is offset by decrease in the weight of the steel members and reduction in foundation costs while providing a immediate occupancy performance.
H. Kit Miyamoto and Amir S.J. Gilani
Miyamoto International, Inc, West Sacramento, CA, USA