Medium and short-term effective prestress losses considering multiple factors: Laboratory and on-site beam experiments

The coupling between the creep and shrinkage of concrete, tendon relaxation, and temperature variations makes it difficult to determine the influence of each individual factor on prestress loss. This study investigates the influence of these multiple factors on the medium and short-term prestress of beam bridges, crucial for their durability and safety. Initially, laboratory experiments were conducted on six model beams to analyze medium and short-term prestress variations. Using a pre-designed scheme, the study isolated and quantified the impacts on effective prestress, with losses calculated through superposition. The findings were compared with existing models, leading to the proposal of a refined model for multiple factors affecting prestress. Then the prestress loss experiments on ten full-sized beams, with thirty-five strands, were calibrated based on the proposed model by regression analysis. Based on the modified model of prestress loss, the mentioned influencing factors would be calculated separately, which agree with the measured data from laboratory and in-situ experiments. In the end, the study concludes that creep has the greatest impact on prestress loss, with other factors contributing to varying degrees. Through full-scale tests, parameters for the prestress loss model were verified. The proposed model in this study effectively describes prestress loss within the tested timeframe. The study further concludes that there existed a time lag in prestress tendons and ambient temperature in both laboratory model beams and in-situ full-scale beams. For practical applications in lift-off tests of effective prestress, the appropriate testing time after tensioning to yield relatively stable results is recommended.