Monitoring and Analysis of a Full Depth Precast Concrete Bridge Deck

Project summary:

The MnDOT Precast Composite Slab Span System (PCSSS) was initially designed by MnDOT with input from University of Minnesota researchers and local fabricators. The bridge system consisted of a series of precast prestressed concrete inverted tee bridge elements that also served as stay-in-place formwork for the cast-in-place (CIP) portion of the deck placed in the field. One of the MnDOT implementations, located in Center City, MN, was instrumented and subsequently monitored for 24 months to investigate reflective cracking and continuity over the piers since the deck was cast. The data obtained from the field study indicated that cracking had initiated in the bridge at the locations of some of the transverse gages in the CIP just above the longitudinal flange joint at midspan and some of the longitudinal gages near the support. The cracking was determined to be the result of restrained shrinkage and environmental effects rather than due to vehicular loads. Transverse load distribution was evaluated with a static truck test. In addition, a two-span laboratory specimen was constructed and load tested to investigate effects of variations in flange thickness, bursting reinforcement, horizontal shear reinforcement, and flange surface treatment. The positive restraint moment that developed at the pier was also monitored for the first 250 days after continuity was made. The data from the laboratory and field tests were analyzed with respect to reflective cracking, transverse load distribution, pier continuity, bursting, and restraint moment, and design recommendations were made.