Quantitative Design of Backup Prestressing Tendons for Long-Span Prestressed Concrete Box Girder Bridges

Abstract

Excessive deflections unexpected at the midspan have commonly appeared in long-span prestressed concrete box girder bridges, mainly because of the high degree of uncertainty in concrete creep and shrinkage, prestress loss, and variations in the environment. Arrangement of backup prestressing tendons that will be tensioned based on deflection development during the service years is an effective solution to this problem. First, an uncertainty analysis of the long-term deformation at the midspan of a bridge was performed using the Latin hypercube sampling method, with the consideration of model uncertainty of creep and shrinkage and random properties of influencing factors; consequently, the 95% confidence interval of the deformation at the midspan was determined. Then, a quantitative design of backup tendons was performed on the basis of the difference between the lower limit and mean value of the 95% confidence interval of deformation. Lastly, the efficiencies of different arrangement schemes of backup tendons were compared, and results show that arrangement of combined external tendons along the girder is the most effective measure for control of long-term deflection.