Experimental Study on Composite Action in Reinforced Concrete–Filled Steel-Tube Shaft Foundations

Abstract

A single enlarged shaft foundation is often used to support bridge columns. In some conditions, it is constructed with a permanent steel casing, which is typically ignored in calculating the structural resistance of the shaft. This study investigated the contribution of this steel casing to the structural resistance and seismic response of single shaft foundations. The composite action between the steel casing and the interior reinforced concrete shaft was investigated. A series of six cyclic large-scale tests were conducted on cantilevering shafts of 50.8- and 76.2-cm diameters with heights of 5.2 and 7.6 m, respectively, with reinforced concrete columns at their top. Different interface conditions were applied to the specimens, which included the natural bond, grease, bentonite slurry, and use of shear mechanisms. In addition to the different interface conditions, the effects of the diameter-to-thickness ratio (D:t) and applied axial load were also considered. The composite behavior of the tested specimens and the plastic hinge development under large deformations were investigated and compared to results from plastic moment calculations.