Experimental Investigation on Nonlinear Flexural Behavior of Post-Tensioned Concrete Bridge Girders with Different Grouting Conditions and Prestress Levels

In past decades, the occurrence of catastrophic collapses in post-tensioned concrete (PC) bridges in several countries has raised major concerns about their load-bearing capacity, calling for numerical and experimental studies on the effects of aging, deterioration, and construction defects. In order to investigate the influence of residual prestressing levels and the imperfect grouting of ducts in PC bridges, we undertook an experimental study on the flexural behavior of six PC girders prestressed with two monostrand tendons having a nearly parabolic route. The specimens' geometry was properly designed based on a 1:5 length scale, assuming a prototype representative of simply supported, beam-type highway bridges in Italy. Two prestress levels were considered as being representative of the expected and defective post-tensioning levels, as observed in several existing bridges. In combination with a different prestressing level, the specimens' ducts were provided with either full grouting, partial grouting, or no grouting in order to consider the whole range of possible bonding conditions for post-tensioning tendons. The girders were tested in a four-point bending configuration under a quasi-static cyclic protocol up to force-based performance levels, followed by a monotonic loading protocol with displacement control up to failure. The different impacts of the prestress level and grouting condition were addressed in terms of the initial (uncracked) behavior, post-cracking behavior, and ultimate capacity. Limited serviceability was achieved in the case of lower prestressing levels, while a 12% to 15% lower load-bearing capacity was attained in the case of unbonded tendons. In the last section of the paper, an analytical study on the initial stiffness and moment-curvature behavior is discussed in support of the interpretation of the experimental findings.