The Effect of Temperature on the Effective Prestressing Force at Release for PCBT Girders

It is important to be able to accurately predict the effective prestressing force because a poor prediction can lead to an increased potential for cracking. If the force is lower than predicted, there is a chance that cracking may occur on the bottom of the section. If the force is higher than predicted, there is the chance that cracking may occur at the top of the section. Recently, studies have indicated that the high temperatures used during steam curing may cause the prestressing force at release to be lower than predicted. The field study presented in this paper was done in order to monitor the influence of steam curing temperatures on the force in the prestressing strands up to the time of release. This field study was designed to monitor the temperature and strains in six full-depth Precast Concrete Bulb Tee (PCBT) sections each 15 ft – 4 in. (4.7 m) long during the curing phase. The changes in the strains and the modulus of the elasticity of the concrete were also measured at release. In addition to the six PCBT test specimens, three full length (70 ft (21.3 m)) beams were cast in the same bed. Due to bad weather and other circumstances, the six PCBT specimens were cast one day and the three full-size specimens were cast the following day.