Live Load Tests of the San Antonio “Y”

Abstract

This paper presents the results of static live load tests performed on several spans of the San Antonio “Y” Project, Phase IIC, prior to its opening to traffic. The San Antonio “Y” Project is an urban viaduct comprising primarily precast segmental box girders erected using span-by-span methods and utilizing a mix of internal and external posttensioning tendons. As part of a comprehensive field investigation, four spans of the project were instrumented to measure overall span deflections, strains in external posttensioning tendons, and concrete surface strains. The four instrumented spans included one end span and the center span of a three-span continuous unit, one span of a two-span ramp unit that was transversely posttensioned to the adjacent main line unit, and one span of a two-span unit connected only with a continuous top slab over the center support (so called “poor boy” continuity). The spans were loaded using combinations of heavily loaded 7-yd short-bed dump trucks positioned to simulate AASHTO MS18 (HS20-44) truckloads. Measurements of span deflections, external tendon strains, and limited concrete surface strains are reported and compared with analytical predictions. Overall, the bridge spans behaved very predictably under static live load conditions.