Slab beam superstructures have been used for short-span bridges since prestressed concrete began to be used in the US. Poor joint performance of these superstructures led to recent revisions to design standards; one example being the Florida Slab Beam (FSB). The FSB and other similar slab beam systems include a composite cast-in-place (CIP) reinforced concrete deck and joint between adjacent beams. An optimized joint design has been developed to accelerate the construction times and eliminate the need for a CIP deck by using ultra-high performance concrete (UHPC) in the longitudinal closure pour to connect the precast members.
The optimized joint design was first developed from eight different cross-section and joint reinforcement details (four 18-inch deep specimens including the control, and four 12-inch deep specimens), investigating the joint transverse service and strength behavior in a small-scale experimental testing protocol. All the specimens were transversely supported and tested under a three-point load setup, applying the load adjacently to the joint region. All 18-inch deep joints performed similar to the current FSB design, while the 12-inch deep specimen with the lowest joint reinforcement placement had the largest transverse strength capacity among those of the same thickness.
The best joint geometry performer from the 12-inch deep specimens in the small-scale protocol was selected to investigate further the overall joint behavior with 30-foot length specimens. Two two-beam test configurations with UHPC joints were developed and experimentally tested under strength and cyclic performance with different loading schemes and support conditions, investigating the load transfer mechanisms, and the demand on the precast concrete, joint reinforcement, and joint interface.
The joint performed well with no observed joint distress or deterioration in performance through the permit service load testing, more than four million cycles of load, and ultimate strength testing of the two-beam systems. Results from these tests and numerical models were used to guide in the subsequent design and construction aids of the new FSB system for accelerated construction to replace aging short-span bridges
