Horizontal Shear Strength of Indirectly Loaded Composite Concrete Beams

Abstract

Four composite concrete beams with cylinder compressive strength of approximately 40 MPa were tested to failure under indirect two-point loading. The first beam, CB1, did not have any ties, and it served as a control specimen. The second and third beams, CB2 and CB3, had 0.11% tie content. The main difference is in the shape of ties; ties in CB2 consisted of individual legs, while CB3 had closed ties. Tie content in CB4 was doubled to 0.22%. The first three beams failed in horizontal shear mode, while the fourth beam failed in flexure. Test results clearly showed that, under indirect loading, the ultimate horizontal shear strength of composite beams could be significantly lower than the American Concrete Institute Code predictions; the specified minimum clamping stress of 0.35 MPa appeared to be unsuitable for indirectly loaded beams. The study also demonstrated that the shape of ties does not have significant influence on the horizontal shear strength, provided there is adequate anchorage of ties on both sides of the interface.