Performance Based Seismic Design UCSF Mission Bay Housing Project

摘要

This paper presents a practical performance based approach to the analysis and design of conventional cast-in-place reinforced concrete residential construction subject to significant seismic demands and hazards at the new University of California San Francisco (UCSF) Mission Bay Campus. The Block 20 Housing (B20) project comprises a large four building residential complex of varying story heights of 7 to 15 stories consisting of cast-in-place reinforced concrete shear wall superstructure founded on varying levels of site soil conditions including liquefiable soils. This paper presents a seismic performance based design methodology used to design the facility and evaluate expected seismic performance levels. In addition to satisfying difficult seismic hazard and site soil conditions in the analysis and design of the superstructure per 2001 California Building Code (CBC) requirements, the University requested additional seismic performance evaluations to predict expected seismic performance for a range of building heights and varying soil conditions. The evaluations using performance based methodologies then served as a basis for defining, optimizing and further refinement of the design to achieve higher seismic performance levels while limiting both cost of construction and potential damage during peak earthquake ground shaking. The approach and methodologies used were based on 1999 SEAOC Blue Book philosophy, as well as, analysis, design and modeling using FEMA 356, 306, 307; and ATC 40 guidelines. The structures designed per CBC requirements included nonlinear static pushover analysis of representative reinforced concrete shear wall frames to determine frame capacities and compare results with acceleration and displacement response spectrum (ADRS) demands to determine expected target building displacements and deformations. These results are then further correlated with expected damage thresholds and predicted seismic performance levels. The analysis included modeling of soil foundation and superstructure interaction including nonlinear pile foundation ductility demands and capacities. The pile foundation substructure strength and ductility capacities were verified to demonstrate that calculated superstructure frame capacities can be developed. Although in some cases CBC building drift limits were exceeded, it was demonstrated that enhanced seismic performance with less damage could be achieved by eliminating a large portion of ductile link beam elements. The project superstructure construction was completed in September 2004 and will be ready for occupancy in September of 2005.