Behavior of adjacent precast prestressed concrete box girder bridges

Precast prestressed concrete adjacent box girders are widely used in short and medium span bridges. Rapid construction and economy are the main attractions of this system. 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 boxes in a number of bridges. The cracking and leakage are mainly due to inadequate design and detailing of the transverse connection between adjacent boxes, which eventually lead to premature deterioration of the bridge superstructure. This research presents a review of the current practices in the transverse design and detailing of adjacent box girder bridges. The PCI Bridge design Manual method for calculating the required transverse post-tensioning force and its design charts are reviewed. Because these charts are outdated, new charts are developed based on the 2007 AASHTO LRFD specifications for live load and dynamic load allowance. The effect of span-to-depth ratio and skew angle are also considered. A simplified design equation is developed to estimate the post-tensioning force per unit length of the bridge as a function of the governing parameters. Two continuous non-post-tensioned transverse connections are proposed as alternatives to the current discrete post-tensioned connections. Proposed connections are designed to transfer transverse shear and moment without end or intermediate diaphragms. The first connection Narrow Joint consists of top and bottom couplers and full depth grouted shear keys. The second connection Wide Joint consists of a wide full depth shear key filled with flowable concrete and top and bottom reinforcement. Finite element models are developed for the analysis of the proposed connections and developing design charts to estimate the required reinforcement for different bridge configurations. Fatigue testing of the proposed connections as well as one of the commonly used connections has been carried out to evaluate the fatigue capacity and joint leakage. Test results have indicated that proposed connections outperform the existing connection. Static load testing and cost analysis of the three connections have demonstrated that the proposed connections have significantly higher flexural capacity in addition to being more economical than the current one