Discussion of “Ultimate Strength of Ribbed Slab Composite Beams with Web Openings” by J. W. Park, C. H. Kim, and S. C. Yang

Abstract

This article comments on earlier research on composite beams with web openings (Park, Kim, Yang, 2003). The beams studied have ribbed slabs with the ribs oriented transversely. The effects of slab width and moment-shear ratio on failure mode and strength were studied and the authors found that the failure mode of concrete slabs depends on the slab width. Strength predictions of a proposed model were also compared with test results and predictions of other strength models. In this commentary, Cho focuses on the truss analogy and discusses several aspects adopted by the authors in the formulation of the shear strength equations at web holes of composite beams against the common knowledge of structural mechanics. Cho makes four points: the authors misunderstood the truss analogy proposed by Cho and Redwood (1992); in the authors' study, the full slab width was assumed to be capable of carrying the vertical shear forces, even though this is not an ordinary understanding of the slab shear behavior; comparisons and evaluations should also include the predictions by the Redwood group methods other than the truss analogy; and the truss analogy predicts better narrow slab beams, rather than wide slab beams.