BART SFO Extension Aerial Guideways: Using Nonlinear Analysis to Control and Minimize Seismic Damage

Abstract

Bay Area Rapid Transit (BART) is extending service from the existing southern terminus of BART, at Colma Station, to San Francisco International Airport (SFO), a distance of 14 km (8.7 mi). Included in this project are approximately 1.93 km (1.2 mi) of aerial guideways. Design criteria required preliminary sizing of guideway columns by using the response spectrum analysis method. Final design required using nonlinear time-history analysis to verify that strains in column reinforcement and concrete did not exceed 60% of allowable ultimate strain. Analysis of the BART guideways by both the response spectrum and time-history methods provides an opportunity to compare the two methods of analysis. Analysis results show that comparable results can be obtained from the two methods under some combinations of structure stiffness and strength. However, wide divergence between the two methods also can occur for other combinations of structure strength and stiffness. Nonlinear modeling also determined that the continuously welded rails with direct fixation fasteners used for the track system on the guideways distribute longitudinal seismic forces and can serve as an effective restraining device across bridge expansion joints.