Seismic Retrofit of Aerial Stations

Abstract

Given the high risk of earthquakes in the San Francisco Bay Area, California, and the essential role of the Bay Area Rapid Transit (BART) system in the region, the BART Earthquake Safety Program has attracted great public attention since the program began. This paper presents a seismic evaluation and describes the retrofit of 11 aerial stations within the BART system. All 11 stations are to be retrofitted to meet safety performance requirements; three of these stations also were retrofitted to meet operability performance requirements. The analytical approaches, seismic vulnerability of as-built stations, and the measures proposed for the BART retrofit effort are presented in detail. It was found that existing bent cap beams and footing caps were insufficient to resist the over-strength demands from columns. Joints between columns and bent caps and joints between columns and footings needed to be strengthened as well. The stations could be upgraded to achieve safety and operability performance requirements through the use of various retrofit measures (e.g., bent cap bolsters, infill walls, fiber-reinforced polymer wraps for columns, footing partial overlays, and footing enlargements).