UC Davis

Performance-based seismic evaluation and retrofit of existing buildings documented in ASCE 41, a professionally recognized standard, contain guidelines and provisions that extend over several analysis procedures. The consistency between the linear and nonlinear analysis procedures outlined in the standard was investigated through the detailed assessment of four existing steel moment frame and concrete shear wall buildings in California. The buildings were instrumented by the California Strong Motion Instrumentation Program, which allowed for the calibration of the structural simulation models against recorded data from past earthquakes. The primary ASCE 41 based assessments of the calibrated models were followed by a comprehensive incremental dynamic analysis (IDA) of each building based on FEMA P-695 to evaluate the collapse probability inherent in the ASCE 41 Collapse Prevention performance level. Finally, a correlation between a system-based drift demand parameter and Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) was established for the four buildings.

This dissertation addresses some of the core issues in ASCE 41 through comprehensive case studies of 3-story and 6-story steel moment frame buildings, and 3-story and 5-story reinforced concrete shear wall buildings. First, options for modeling of the primary structural components are explored, followed by a system-based calibration of the model against displacement and acceleration time histories in past earthquakes recorded at the site. For the steel buildings, a major focus was on obtaining the nonstructural stiffness contribution at low intensities, and understanding how the contribution of nonstructural components diminishes during strong shaking. For the concrete buildings, extensive effort was devoted to modeling options for flexural-controlled versus shear-controlled walls.

The ASCE 41 assessments demonstrated inconsistency between the four analysis procedures. The linear static and linear dynamic procedures produce similar component demands, drifts, and performance levels but were shown to be conservative compared to the nonlinear procedures. The nonlinear static and nonlinear dynamic procedures differed significantly in component-demands and drift patterns, and the static procedure underestimated the demands in the upper stories of the six-story steel building. These basic assessments were followed by incremental dynamic analyses and collapse probability fragility curves were developed based on an assumed collapse condition at 6% story drift. Results from the simulation studies indicate that the current component-based Life Safety and Collapse Prevention performance levels are conservative and a quantified comparison is presented using a drift-based approach. Findings from this research work indicate the need to modify the current acceptance criteria for each performance level to include a system-based demand criteria. The dissertation concludes with recommendations for future research focused on developing methodologies to augment acceptance criteria as well as the need for improved guidelines for shear-controlled walls and ground motion scaling for hazard-consistent assessments.