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INTRODUCTION

One of the strongest earthquakes ever to hit California shook hundreds of post-tensioned buildings on October 17, 1989, with an intensity of 7.1 on the Richter scale. The earthquake, named Loma Prieta, had its epicenter approximately 65 miles southeast of downtown San Francisco (Figure 1a and 1b). Widespread damage was caused in the vicinity of the epicenter and as far as San Francisco and Oakland.

Many post-tensioned buildings are located in the area impacted by the strong motion. These buildings were constructed over a period of time extending as far back as late 1950 to the present. Earlier post-tensioning systems, such as button head wires, paper wrapped tendons as well as examples of the most recent product, namely the greased and extruded strands are among the buildings located within the affected area.