Flexural behavior of continuous concrete beams prestressed with bonded and unbonded tendons

The use of unbonded tendons in prestressed beams is becoming an increasing popular option for the repair and strengthening of bridges, high-rise buildings, and foundation systems. However, there has been an increase in load demands on these structures as well as the need for repair to damaged sections throughout the lifespan of the structure. Thus, the need for a new, more effective way to design these prestressed members to meet ever growing demand of these structures is evident. The main objective of this study is to investigate the performance of continuous beams prestressed with both bonded and unbonded tendons, known as hybrid beams. This investigation included the casting and testing of three continuous high strength concrete (HSC) beams prestressed with hybrid tendons. The results of this study include number of cracks, load-deflection behavior and load-strain behavior as well as an analysis of available hybrid code equations in their ability to predict the behavior of such hybrid beams. Based on the analysis of the experimental results, it is shown that the current code equations do not accurately predict the stress at ultimate and there is a need to provide more simplified and accurate equations.M.S.Includes bibliographical reference