While the study of non-composite castellated beams have received much attention, very little work has been done on composite castellated beams. The effect of the composite concrete slab is to significantly increase the flexural resistance of a steel section; it is however uncertain what effect this will have on the shear resistance. In this research project tests to destruction of five composite castellated beams were performed, and relate to previous tests on non-composite castellated beams. Ultimate failure loads of the three shear critical test beams were associated with web-post buckling, comprising double curvature bending. The remaining two flexural test beams failed when most of the studs in one-half of the span failed, resulting in lateral torsional buckling of the suddenly unconstrained flange. A numerical study using the finite element method was then employed in investigating the nonlinear buckling behavior of the web-posts in shear critical composite and non-composite castellated beams. Buckling of the web-posts was observed to be the dominant mode of failure in all finite element models; the composite beams were found to have significantly higher ultimate shear carrying capacities than their non-composite counterparts. It was found that the effect of the composite slab is to reduce the shear force in the web-posts, thus increasing the beam ultimate shear carrying capacity. Finally, yield analyses were performed on castellated beams using moment-to-shear interaction diagrams originally developed for isolated web openings. Results based on yield failures were found to be in good agreement with the test failure loads for the flexure critical beams. Yield analysis tended to slightly overestimate the failure loads for the shear critical composite test beams, due largely to the buckling failures of the web-posts in the tests. (Abstract shortened by UMI.)

Redwood, R. G. (Supervisor)