Shear Resistance of Circular Concrete-Filled Steel Tubes

Abstract

Concrete-filled steel tubes (CFSTs) and reinforced concrete-filled steel tubes (RCFSTs) are used throughout the world in tall buildings and bridges. They are becoming increasingly popular in the United States transportation sector as bridge piers, piles, or shafts where lateral spreading and liquefaction potentials can create large shear demands that control member design. Prior research indicates that CFSTs have superior strength, stiffness, and inelastic deformation capacity compared to their reinforced concrete and structural steel counterparts. This has been well defined for flexural and axial behavior; however, few studies have been done to assess the shear carrying capacity of these members. For design, most provisions either reference one of the two materials, steel and concrete, or some combination of the two, without acknowledging the increased capacity that comes from their interaction. Past research has been performed on small diameter CFSTs (~ 6 in.) that has shown these methods greatly underestimate shear resistance. This program extends this knowledge with the experimental testing of larger-scale CFSTs (20 in. in diameter) and the development of a finite element model, validated against these tests, that was used for further parametric studies. The experimental study varied parameters including aspect ratio (a/D), diameter-to-thickness ratio (D/t), concrete compressive strength, tube type, tail length, internal reinforcement, and interface condition. Parameter studies then expanded this data set to include variation in tube steel yield strength and axial load ratio. The results from these investigations, and prior research studies, were used to develop limit state criterion and quantify shear capacity with a new design expression incorporating the composite nature of all components and enhanced properties due to axial load.