Shear strength of concrete-steel hybrid bridge girders

Twenty approximately half-scale elements were tested to investigate the vertical and horizontal shear resistances of a unique hybrid bridge girder consisting of a reinforced concrete web and steel plate flanges. A variety of failure modes were observed in the tests. Horizontal shear failures due to stud fracture or stud pull-out occurred in specimens with widely spaced studs. Elements with more closely spaced shear studs failed in a vertical shear mode, with crack slip being common in elements with light stirrups, and concrete shear failures being more prevalent in elements with heavy stirrups. Horizontal slip along the flange-web interface was eliminated by using a tapered web with more concrete and confinement reinforcement surrounding the studs. Comparisons of the measured strengths with those obtained using the Canadian Standard S6-88 ultimate strength design procedure for stud shear connectors demonstrated surprisingly good agreement. Similarly, comparisons with vertical shear design procedures in both CSA S6 and the draft Canadian Highway Bridge]Design Code (CHBDC) showed good agreement, except that the shear stress limit in CSA S6 is overly conservative. The CHBDC method generally predicts larger vertical shear strengths of the the hybrid girders because it accounts for the beneficial effects of the steel flanges in reducing the axial strains of the concrete web.