Experimental and numerical study on shear behaviour of concrete-filled double-skin steel tubular structures

The concrete-filled double-skin steel tubular (CFDST) structures show high strength, large stiffness and convenient construction, which has been adopted in engineering practice more and more widely. However, the nonlinear shear behaviour of CFDST is still lack of research when the shear span ratio is low. This study conducts shear tests on four CFDST deep beams with large diameter of 1500 mm as well as low shear span ratio of 0.33 and 0.83, based on the application of CFDST in a typical nuclear engineering. The failure modes, load-displacement relations, concrete cracks and strains on steel tubes are carefully analysed. Then a refined nonlinear finite element model is built and the shear mechanism of the CFDST is revealed. The shear contribution of various components is obtained including the outer and inner steel tubes, the in-filled concrete, the stiffeners. Parametric analysis is further conducted to find the influence of key design parameters including hollow ratio, material strength and thickness of steel plate. Finally, based on test results and finite element analysis, a shear capacity formula considering the superposition of concrete, steel tube and stiffeners is proposed. It is demonstrated that the CFDST beams show typical shear failure for shear span ratio of 0.33 while shear-flexure failure for shear span ratio of 0.83. The shear strength is high with satisfied ductility. The proposed formula gives accurate prediction which is verified by test results and finite element analysis.