N. Mangoba
Published: 1999
Total Pages: 0
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Four new post-tensioned, box girder bridges in Northern Nevada were instrumented during construction to collect data on the possible adverse effects of high variation in relative humidity (RH) and temperature on prestress losses. The bridges were monitored at short intervals during the first month after stressing and in two-month intervals afterwards. For each bridge, the measured data consisted of concrete surface strains on two girders, creep strains on concrete cylinders at the bridge sites, shrinkage strains on cylinders at the site and at the laboratory, and deflection of the midspan relative to the ends of the structures. The actual time-dependent prestress losses were compared to two current loss prediction methods: the AASHTO lump-sum estimate of prestress losses and the time-step methos of determining losses by Naaman. To determine the effects of changes in RH on the losses, the climatic data of the area were incorporated into the calculated losses.