Performance based design of buildings to assess damage and downtime and implement a rating system

Abstract

The Christchurch earthquakes have highlighted the mismatch in expectations between the engineering profession and society regarding the seismic performance of buildings. While most modern buildings performed as expected, many buildings have been, or are to be, demolished. The ownership, occupancy, and societal costs of only targeting life-safety as the accepted performance standard for building design are now apparent in New Zealand. While the structural system has a significant effect on the seismic performance of the entire building, including the contents, it is only about 20% of the total building cost. Hence, structural engineers should view the seismic performance in a wider context, looking at all the systems of the building rather than just the damage to structural items and life-safety. The next generation of performance-based seismic design procedures, outlined in the FEMA P-58 document, provide engineers with the tools to express the seismic performance of the entire building in terms of the future life loss, facility repair cost and repair time. This paper will outline the FEMA P-58 procedure and present the results of a comparative study of six different structural systems for a three storey commercial and laboratory building: moment frame; buckling restrained braced frame; viscously damped moment frame; Pres-Lam timber coupled-walls; cast-in-place reinforced concrete shear wall; and base isolated braced frame. Each system was analysed as a fully non-linear structure and the calculated drifts and floor accelerations were input into the FEMA P-58 PACT tool to evaluate the overall building performance. The PACT tool performs loss calculations for the expected casualties, repair cost, and repair time from which a QuakeStar or SEAONC rating for the building can be obtained.