Horizontal shear strength of composite concrete beams with a rough interface

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The design provisions dealing with horizontal shear of composite concrete beams in different codes are mostly based on push-off tests and are conservative. Previous investigations on composite beams were not useful because most of the test beams failed in modes other than in horizontal shear. Therefore this study is aimed at providing the required insight into the behaviour of such beams with a rough interface. Previous research dealing with this area and the related topics are discussed in a chronological order. The requirements of CSA-A23.3 and ACI-318 dealing with horizontal shear are critically reviewed. The specifications of these codes appear to be irrational and unduly complicated. The relevant provisions of major codes of other countries are compared with those of the CSA code. A typical composite concrete beam was analyzed using three dimensional finite element analysis with an ANSYS program accounting for material non-linearity. The joint in the beam was modelled with interface slip elements. The shear stresses in the beam were found to match qualitatively the shear stresses predicted by using VQ /lb. Sixteen simply supported beams were tested to examine their capacity to develop horizontal shear. These beams were designed to fail in horizontal shear prior to failing in any other mode. To simplify construction, the top surface of the precast girder was left with an as-cast surface. Relative slips between the precast web and cast-in-place flange were closely monitored in every beam using a new type of slip gauge developed in this study. The details reported include slip characteristics, stirrup strains, deflections and crack widths of the beams. The results show that the codes are overly conservative particularly for small steel ratios. The use of an as-cast surface on the precast beam is intended to simplify production of these beams. The parabolic equation which has been formulated closely fits the results from the present work and tests of others. Detailed revisions are suggested for the CSA and ACI codes. The equations suggested for these codes are also valid for general cases of shear transfer in concrete including lightweight concrete.
Bibliography: p. 228-235.
Patnaik, A. K. (1992). Horizontal shear strength of composite concrete beams with a rough interface (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/16714