Analytical model for predicting prestress transfer bond-related parameters of 18 mm prestressing strands

Abstract

The bond between prestressing strand and concrete is necessary for the composite-action of the two materials. This study develops an analytical model to investigate the bond performance of 18-mm prestressing strands. The model considers the concrete compressive strength for both conventional and self-consolidating concrete. It is then used to determine the short- (at prestress transfer) and the long-term (after all prestress losses) transfer length and strand end slip. The predicted short-term transfer length and strand slip values were validated with the experimental results obtained from several pretensioned concrete beams and girders, which had various geometric configurations, concrete compressive strength, and number of prestressing strands. The results showed that the model provided a reasonable prediction of bond performance. From the analysis of the predicted long-term transfer length and strand end slip values, the long-term transfer length is on average 33% longer than the short-term transfer length, whereas the increase in strand end slip is on average 24% from the short-to the long-term stage. Regardless of concrete compressive strength and concrete type (conventional and self-consolidating concrete), both the ACI-318 and AASHTO LFRD codes provided a conservative limit for the predicted long-term transfer length values.