Cyclic-shear behavior of square thin-walled concrete-filled steel tubular columns with diagonal ribs

Abstract

There is no doubt that stiffeners for square concrete-filled steel tubular (CFST) columns can improve the composite action in terms of delaying local buckling of steel tubes and enhancing the confinement on infilled concrete. Among various proposed stiffening forms, diagonal binding ribs, made of perforated thin-walled steel plates and welded at all the four pairs of adjacent sides of a square tube, are found particularly effective. Recent research has experimentally evaluated the axial compressive and cyclic-bending behavior of square thin-walled CFST columns stiffened by diagonal ribs. However, further investigation is necessary to better understand their cyclic-shear behavior. In this work, four diagonal ribs stiffened square thin-walled CFST columns and one unstiffened counterpart were designed and tested under combined cyclic-shear load and constant axial compression. Main parameters included the shear span to depth ratio, axial load ratio, width-to-thickness ratio of the steel tube, and thickness of diagonal ribs. Test results showed that the diagonal ribs improved the confinement from the steel tube to the infilled concrete. The stiffened specimens exhibited satisfactory cyclic-shear behavior with much higher load capacity, better ductility and larger energy dissipation than the unstiffened counterpart. Numerical modeling of the shear specimens was then conducted, indicating that the concrete and steel part contributed to the shear strength by 41.3%-57.4% and 42.6%-58.7%, respectively. Finally, the test results were compared with current design provisions, the average ratio of the predicted to tested shear strength were 0.60 and 0.66 for the calculation methods in the AISC specification and Eurocode, respectively.