Methodological Aspects in Measurement of Strand Transfer Length in Pretensioned Concrete

摘要

This study assessed experimental methodological factors that might affect the estimation of transfer length of pretensioned concrete to minimize trials and errors in experimental works and increase the credibility of test results. The authors analyzed the accuracy and reliability of various measurement alternatives employed in this study. Acceptable performance was demonstrated when electrical resistance strain gauges (ERSGs) were placed on strands' surfaces at intervals of 5.9 in. (150 mm) and on concrete surface with the cover thickness of the concrete that is not greater than 3.0 in. (75 mm). Therefore, ERSGs that are bonded on either strands or concrete surfaces may be a viable option for reliable measurements of transfer length. It was also found that strain readings from gauges mounted on strands fan be used to estimate the amount of prestress through an adjustment process. High-temperature steam curing somewhat adversely affects transfer length; and when strand is debonded near the end as is common in the fabrication of precast prestressed concrete, a significant reduction of transfer length may occur, especially at the cut end. The application of a sudden deten-sioning method by disc cutting produces different transfer lengths at each cut and dead end.