Axial capacity of circular hollow section T-joints using grade HSB 600 steel

Abstract

Because of their structural efficiency and aesthetic appeal, steel circular hollow sections have been used in the construction of a wide range of structures. As more high-rise and long span buildings are built, there has been an increase in demand for high strength steel with sufficient ductility. Steel of grade HSB (High performance Steel for Bridge) 600, with a minimum tensile yield stress (F-y) of 480 N/mm(2) for all thicknesses, was introduced in the Korea Building Code (KBC 2009, 2009). However, current design standards may not be applicable to circular hollow sections with steel of grade HSB 600 since the current provisions were established based on tests of steels with a yield strength of up to 355 MPa and a yield ratio of up to 0.8. For joints with large deformation, the yield strength can be increased up to 460 MPa with a resistance factor of 0.9. This paper investigates the strength limits and various possible failure modes. Eight full scale circular hollow section T-joints were tested and analyzed to investigate the applicability of current design standards. Two test series depending on the grade of steel, i.e., SHB600 and SS400, with specimens in each series were tested with variations in the ratio of diameter to wall thickness of chord member (D/t) and vertical member (D-t/b(t)). All chord members were 3,000mm and vertical members were 1,950 mm in length. For chord members, 750 mm diameter with 12 mm and 26 mm wall thicknesses were used for the tests. For vertical members, 650 mm diameter with 12 mm and 40 mm wall thicknesses were used. The effects of the experimental parameters were evaluated for their applicability to current standards based on the limited test and analysis results of the circular hollow section T-joint.