Performance and Safety of Current Versus Bi-Level Design Procedures-Impact of Northridge Earthquake

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9415726 Wen Building design procedures in this country have been aiming at life safety under a design earthquake of a given return period. It is basically a single-level design. A valuable lesson learned from recent earthquakes, in particular the Northridge earthquake, is that damage and economical loss may be just as an important issue as life safety. Design for more than one level of earthquake has been used in other countries of high seismicity such as Japan and New Zealand in which serviceability and ultimate limit states are explicitly considered. The extensive data collected from the Northridge and other recent earthquakes in Southern California provide and opportunity for us to take a critical look at the safety and performance of the current procedures versus alternative bi-level procedures. The research projects is under taken here with the following specific objectives: (1) To evaluate and compare the performance and safety of buildings designed in accordance with the current and alternative procedures. (2) To evaluate the long- term risk implications of the above design procedures and develop strategy implication of the above design procedures and develop strategy for formulating more rational, risk-consistent code procedures. To achieve the above objectives the following tasks are necessary; (i) Analysis of Northridge data to update, the seismic risk and the site specific ground motion models used in current reliability evaluation of structural performance in which dependence on seismic source, path, and site characteristics is considered. (ii) Design of low-rise (under 12 stories) steel and reinforce concrete buildings according to the 1991 UBC and alternative bi-level procedures at selected sites in the Los Angeles area. (iii) Perform dynamic response analyses of the building and compare response behaviors and response statistics of these two designs. (iv) Perform long-term risk analysis of designs according to the two procedures us ing the updated seismic risk and ground motion models and compare risk implications. (v) Identify advantages and shortcomings of alternative versus current design procedures and suggest areas for improvement in future codes. The research conducted will provide insight to this important problem which has a profound implication in research as well as practice in US and abroad. This is a Northridge Earthquake Project.