Theoretical modeling is presented for the prediction of prestress loss of strands during the steam curing process. The model comprises heat transfer model, bond-slip model at elevated temperature and micromechanical model for prestress loss. The model was able to predict the experimentally measured prestress loss in a reasonable accuracy.

During the steam curing process, some initial prestress is lost due to the effect of high temperature. Limited number of quantitive evaluation has been reported on thermal loss of tendon during steam curing process. In this study, a theoretical evaluation was derived for the amount of prestress loss in prestressed concrete member during steam curing process. The equation devide overall process to 3 stages : from initial state to bonding state between concrete and tendon; just before cutting; and after cutting. The evaluation predicted the amount of prestress loss in the order of 7% of initial prestress force by direct thermal effect through all curing procedures. To validate the equation which estimate the amount of prestress loss, experimental studies should be performed.

Complete closed-type carbon fiber reinforced polymer stirrups with a rectangular section (CFRPRS) were developed and tested in this research. The CFRPRS was intended to relieve stress concentration and to reduce the number of kinked fibers at the bent portion. A total of 16 B.5 specimens were tested regarding the bend strength of the CFRPRS and CFRP stirrups with circular section. Test results showed that CFRPRS improved the bend strength compared to its counterpart of conventional CFRP stirrups having a circular section, with the larger ratio of width to thickness being more effective for the same sectional area. The best correlation between the test results and predictions on CFRPRS bend strength was observed when the section of CFRPRS was modeled as a collection of transformed individual circular sections.