Impact of longitudinal tendons on long-term deflections of long-span concrete cantilever bridges

For over ten years, excessive deflections at the mid-span have commonly appeared in long-span prestressed concrete box girder bridges during their service years, especially for the segmental, cast-in-place concrete cantilever bridges. This paper is initiated with the objective to improve the deflection problems by designing longitudinal tendons. First, the development of design of tendons for long-span concrete cantilever bridges in China was discussed, and results indicated that the layout of cantilever web's bent-down tendons was an effective means to avoid the web's inclined cracks which were very harmful to the long-term deflections. Moreover, some approaches to mitigate deflections, such as pre-setting internal tendons and external tendons tensioned during their service years, or internal and external tendons all tensioned before completion of the bridge, were introduced, and the impact of them on long-term deflections was analyzed. Also, the efficiency of different layouts of external tendons was compared for improving the deflections problems.