Post-tensioned Tendon Losses in a Spliced-Girder Bridge, Part 1: Field Measurements

Abstract

As part of the reconstruction of Interstate 15 through Salt Lake City, Utah, the bridge over 4500 South Street was built with a segmental section using the new Washington State Department of Transportation precast concrete deep girder design. The northbound bridge consists of eight post-tensioned, spliced, precast concrete girders that have three segments each, for a single clear span of 61.44 m (201.6 ft). Four girders and portions of the bridge deck and parapet wall were instrumented and monitored for three years and eight months. Data recorded from the bridge included concrete strain at selected girder locations and girder post-tensioned losses and deflections for one of the girders. At the end of the monitoring period, the actual losses at midspan in the instrumented girder (including time-dependent losses and anchorage seating and friction losses) were on average 14.5% of the initial post-tensioning force. The absolute upward midspan deflection was 0.15% of the clear span, and the two splice points exhibited almost identical deflection, indicating excellent girder/splice continuity performance. This paper describes the instrumentation and field measurements of the monitoring study. Part 2 of this paper, which will appear in the July-August 2007 issue of the PCI Journal, will present the analysis of losses.