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

Full-scale precast concrete deck slabs designed for bridge structures were tested to failure under simple bending with varying levels of roughness between the precast concrete slab and cast-in-place concrete topping slab. Because no horizontal shear slip occurred between the precast and cast-in-place concrete slabs, the behaviors were nominally the same for the three tests loaded in positive bending. In an earlier paper, Dowell compared the measured and predicted force-deformation results, which had good agreement, until the onset of failure, with nonlinear prediction analyses based on flexural response only. Not considered before the tests, as reflected in the prediction analyses reported in the earlier published study, was the flexure-shear mode of failure observed for all three tests. The structural tests demonstrated that the precast and cast-in-place concrete slabs acted compositely to large displacements, with the final failure plane occurring through both slabs as if they were one, at a single, wide-open, inclined flexure-shear crack. Because the purpose of the structural tests and analyses was to demonstrate that precast and cast-in-place concrete topping slabs act compositely under working loads, a complete understanding of the failure mechanism was of secondary importance to the project because this occurred at displacements well beyond the desired performance. It is of interest now, however, to revisit the data and observed behaviors from the structural tests to give a more complete picture of the failures, especially because critical crack widths were measured throughout the tests but were not previously published. In this paper, the measured and observed shear failures for all three composite slabs tested in positive bending are compared to analytically determined force and displacement values at failure. This is found using the modified compression field theory and geometry considerations of a simple beam with well-defined and idealized flexure-shear cracks. Theoretical and measured crack widths and plastic hinge rotations at midspan are also compared in the paper.