Evaluating and improving the seismic performance of older tall buildings

The seismic performance of new tall buildings located in regions of high seismic hazard has been recently investigated by Pacific Earthquake Engineering Research (PEER) Center under its Tall Buildings Initiative (TBI) program. The Tall Building Initiative has now expanded to assess the seismic performance of existing tall buildings. Buildings being considered are 20 stories or more in height, and constructed on the West Coast of the U.S. between about 1960 and 1990. During this period, several hundred tall buildings were constructed in California, but earthquake-resistant design procedures had not yet been fully developed. From these structures, a 35-story steel building, designed in 1968, and having representative details from that period, was selected for evaluation. In this paper, results of three-dimensional nonlinear analysis models developed to assess the seismic performance of this structure are presented. Two earthquake hazard levels are used for the evaluation. Structural analysis results are interpreted to assess the impact of suspected deficiencies on seismic response, and the ability of different evaluation guidelines, numerical models and analysis methods to identify seismic vulnerabilities. A feasible retrofit strategy was identified. Recommendations are offered for further research and guideline evaluation.