Hysteretic behavior and modified design of square TSRC columns with shear studs

The tubed steel reinforced concrete (TSRC) column is a composite member consisting of the concrete core reinforced by a steel shape and the outer thin-walled steel tube which is made slightly shorter than the column to avoid direct axial loading and acts as a confining steel for the concrete. In this paper, the hysteretic behavior of square TSRC columns was investigated experimentally and analytically. Five square TSRC columns, in which high-strength concrete with f_cu,150 = 85.4 MPa was used and the thin-walled steel tube in potential plastic hinge zones was stiffened by steel plates, were tested under constant axial compression and cyclic lateral loads. The influences of shear studs on the steel shape, axial load ratio, width to thickness (D/t) ratio were also considered in the test. The test results indicated that the confinement from steel tubes effectively improved the ductility and plastic deformation ability of the specimens, while the shear studs on the steel shape effected little on the co-working behavior between the concrete and the steel shape. A fiber-based element model using OpenSEES software was developed and a good agreement was achieved between the test and predicted results. Utilizing the numerical model, the limiting axial load ratio was analyzed to ensure that the square TSRC columns had the sufficient ultimate deformation capacity. To account for the improvement of strength and ultimate strain in the concrete core resulting from the tube confinement, relevant development methods for N-M interaction diagrams, such as those in the ACI and EC4, were modified for square TSRC columns.