Behavior of two long-span high strength concrete prestressed bridge girders

Two full size long-span composite prestressed bridge girders were constructed using high-strength concrete (28-day compressive strengths exceeded 83 MPa [12,000 psi]) to investigate transfer length, camber, prestress losses and fatigue life. The AASHTO relationship for transfer length was found to be conservative for large diameter prestressing strands (15.3 mm [0.6 in.]) spaced at 50.8 mm (2 in.) on center in high strength concrete. Load - deflection response to simulated truck load and overload testing was predictable. Loads required to initiate flexural cracking were much lower than expected in one of the girders for which initial shrinkage cracks were observed prior to strand release. Upon release, the shrinkage cracks were observed to close completely. The initial shrinkage crack closure and its effect on camber, prestress losses, and flexural cracking loads was quantified using geometric compatibility.