Full-Scale Experimentation of Pre-stressed Concrete Girders During Post-tensioning

The use of post-tensioning in construction has revolutionized the construction industry and made way for a number of construction and structural applications that were unattainable before. One of the most important topics that is synonymous with the use of post-tensioning is the matter of accurately calculating the losses that arise in pre-stress, more specifically the short-term losses and long-term losses. One of the more prominent types of losses is the friction losses that occur during the jacking of the concrete elements. In this paper, the matter of friction losses in pre-stress will be explored by utilizing an on-site experimental investigation on real scale 30-m-span bridge girders. This provides great accuracy and reliability in the obtained results as the need to perform scaled modeling is eliminated. The research at hand incorporates an experimental setup in order to utilize strain gauges along the tendon length embedded in a concrete girder in order to accurately measure and map out the loss of strain that occurs in the tendons as compared to the tendons length, along with the pilot laboratory testing that were conducted in the labs before the site experimentations with the aim of perfecting the experimental setup. In total, 7 girders were tested on site in order to obtain the readings that will be used in the statistical analysis and findings of the research project. The behavior perceived in a large proportion of the tested girders is consistent with the expected behavior in the theory and literature with regard to the strain gain and strain loss throughout the different stages of girders jacking. Additionally, the perceived behavior shows that there is a shift in the values of the strain between different stations of the same tendons, meaning that the value of the strain measured decreases the further we move from the jacking end.