SHEAR-STRENGTH OF CONCRETE-STEEL HYBRID BRIDGE GIRDERS

Twenty approximately half-scale elements were tested to investigate th e 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 sh ear failures due to stud fracture or stud pull-out occurred in specime ns with widely spaced studs. Elements with more closely spaced shear s tuds failed in a vertical shear mode, with crack slip being common in elements with light stirrups, and concrete shear failures being more p revalent in elements with heavy stirrups. Horizontal slip along the fl ange-web interface was eliminated by using a tapered web with more con crete and confinement reinforcement surrounding the studs. Comparisons of the measured strengths with those obtained using the Canadian Stan dard S6-88 ultimate strength design procedure for stud shear connector s demonstrated surprisingly good agreement. Similarly, comparisons wit h vertical shear design procedures in both CSA S6 and the draft Canadi an Highway Bridge]Design Code (CHBDC) showed good agreement, except th at the shear stress limit in CSA S6 is overly conservative. The CHBDC method generally predicts larger vertical shear strengths of the the h ybrid girders because it accounts for the beneficial effects of the st eel flanges in reducing the axial strains of the concrete web.