Modeling of Bond Stress\u2013Slip Relationships of a Strand in Concrete during Steam Curing

Abstract

The restrained thermal expansion of a pretensioned strand causes thermal prestress loss during steam curing until sufficient bond strength develops. The amount of thermal prestress loss is directly related to the characteristics of the interfacial bond stress–slip relationship at different maturity phases of concrete. For a rational assessment, the bond stress–slip relationship needs to be investigated experimentally at different maturity phases. In this study, a total of 12 pull-out tests were performed using seven-wire strand of 12.7 mm diameter, at different concrete equivalent ages of 7.8, 23.5, 53.8 and 85.2 h. Based on the test results, an empirical model of the bond stress–slip relationship was developed. The model comprised four segments: a curvilinear ascending region, a constant maximum region, a linearly descending region, and a region of constant frictional bond stress. The characteristic values in the model were expressed as functions of equivalent age. The model was able to predict the test results with reasonable accuracy.