Flexural Behavior and Strut-and-tie Model of Joints with headed bar details Connecting Precast Members

This paper focuses on an investigation of an improved longitudinal joint with headed bar details connecting precast decked bulb tee girders for accelerated bridge construction. The testing study included two phases. In phase I, five beam specimens with various headed bar details and a continuous reinforced specimen were tested under flexure loadings. A headed bar detail with 152 mm lap length was recommended for further study. In phase II, two slabs connected by the selected joint were tested under flexure and flexure-shear loadings. Test results were evaluated based on structural behaviors including capacity, deflection, and failure mode. At last, a validated strut-and-tie model was developed to anticipate the capacity of the improved longitudinal joint. It shows that the proposed headed bar details can provide a continuous force transfer in the joint. The lap length interacting with the spacing of the headed bar is the most significant parameter of the improved joint details. To develop a full strength joint, the lap length should not be less than 152 mm and be designed by the strength requirement. The strut-and-tie model can provide a conservative strength anticipation of the joint and it is the lower bound of the ultimate capacity of the joint