Flexure-shear behavior of precast concrete deck panels with cast-in-place concrete topping

Shear failures were observed at large displacement for all three full-scale decks tested in positive bending. The composite concrete deck consisted of a prestressed, precast concrete deck unit with a cast-in-place concrete topping slab that completed the section and provided the final riding surface on a bridge. Failures occurred along a single flexure-shear crack plane. In this study the onset of shear failure and the degrading response after shear failure were investigated. The results demonstrate that it is possible to determine the force and displacement at shear failure by finding the intersection of the force-deformation curve from flexural analysis1 and the degrading shear strength deformation curve from the modified compression field theory, as well as geometric considerations of the structure. For these deck slabs, the initial shear strength was greater than the demand. This allowed the majority of the behavior to be determined from flexural analysis. However, the shear strength decreased quickly as a function of crack width and related vertical displacement, and the final failure at large deformation was from shear. This final failure mode occurred at displacements that will not be seen in the field from service load or from extreme earthquake loading. This study demonstrated that the measured slow decline in force with increased displacement following peak force for two of the deck slabs was due to the onset of shear failure. This was not clear at the time of the tests or when writing the first paper 1 on these tests. By comparing theoretical and measured crack widths, the onset of shear failure is clearly defined as an unstable crack-width growth at one of the flexure-shear cracks with a simultaneous reduction in width at the other cracks. In all three cases, crack widening occurred at the critical flexure-shear crack immediately following peak force and the onset of shear failure.