Concrete-Filled Steel Tubes as Coupling Beams for RC Shear Walls

Publisher Summary This chapter explores the use of Concrete-Filled Rectangular Tubes (CFRTs) as coupling beams, and describes an experimental investigation into this form of construction to study their load carrying capacity, ductility, and energy absorption characteristics. In such tubes, the concrete infill prevents the inward buckling of the tube wall, while the steel tube confines the concrete and constrains it from spalling. The combination of steel and concrete in such a manner makes the best use of the properties of both materials and leads to excellent ductility. Eight cantilever beams consisting of two control rectangular hollow section tubes and six CFRTs were tested. All tubes had a wall thickness of 2 mm, with a cross-sectional height of 200 mm and width of 150 mm. The variable for the CFRTs was the concrete strength, designed to cube strengths of 40 MPa ,60 MPa, or 90 MPa. In static loading tests, the specimens were monotonically loaded until failure. The strains and displacements were recorded at different load levels, from which load-deflection curves were plotted. Local buckling was observed on both flanges of all the cyclic test specimens. During load reversal, a buckled flange was straightened again under tension. The compression-tension cyclic stresses caused degradation in both steel and concrete, so that the maximum load reached in a cyclic test is considerably lower than that in the corresponding static test.