Transverse post-tensioning design and detailing of precast, prestressed concrete adjacent-box-girder bridges

Abstract

Precast, prestressed concrete adjacent box girders are widely used in short- and medium-span bridges. Rapid construction and low construction cost are the main attractions of this system. Also, the continuous flat soffit and relatively high span-to-depth ratio make this system aesthetically pleasing. However, reflective cracking and leakage have been reported along the longitudinal joints between adjacent box girders in a number of bridges. The cracking and leakage are mainly due to inadequate design and detailing of the transverse connection between adjacent box girders, which eventually leads to excessive differential displacement and rotation of adjacent box girders. The reflective cracking and leakage allow chloride-induced corrosion of reinforcing steel and prestressing strand and premature deterioration of the bridge superstructure. This paper presents a review of the various practices in the transverse design and detailing of adjacent-box-girder bridges. The basis for calculating the transverse post-tensioning force according to PCI's Precast Prestressed Concrete Bridge Design Manual is discussed. Design charts and equations were developed for various combinations of span length, bridge width, skew angle, and girder depth using the latest loading from AASHTO LRFD Bridge Design Specification. These aids may be viewed as an update to the information in section 8.9 of the PCI bridge design manual, which was based on an earlier version of the AASHTO standard specifications.