Hysteretic behavior of square thin-walled CFST column stiffened by diagonal ribs
Zhou Zheng1,2 Gan Dan1,2 Zhou Xuhong1,2
1. Key Laboratory of New Technology for Construction of Cities in Mountain Area of the Ministry of Education,
Chongqing University, Chongqing 400045, China; 2. School of Civil Engineering, Chongqing University, Chongqing 400045, China
Abstract：Welding diagonal ribs welded on the adjacent edges of the square steel tube can effectively enhance the local buckling capacity of the square thin-walled steel tube, and thus the mechanical performance of this composite column can be improved significantly. Four cyclic tests were carried out to investigate the hysteretic behavior of the square thin-walled CFST columns with diagonal ribs. The main parameters were holes in the diagonal ribs, axial load ratio, and width-to-thickness ratio. The test results indicated that all specimens failed with the formation of a rotational plastic hinge at the base. It was also observed that the steel tube bulged, the welding fractured between the steel tube and diagonal ribs, the concrete crushed, and the load-displacement curves were stable and full; the ductility coefficients and ultimate drifts of all specimens were larger than 3.3 and 1/30, respectively. The holes in the diagonal ribs affected the specimen behavior little. Decreasing the width-to-thickness ratio or increasing the axial load ratio could effectively improve the load capacity but would reduce the deformation capacity. The strain analysis results indicated that the diagonal ribs stiffened steel tube could confine the concrete uniformly, and the steel tube and diagonal ribs could work as a whole. The model based on ABAQUS software could simulate the load capacity and deformation capacity with reasonable accuracy. The parametric analysis showed that the concrete strength and axial load level had a significant effect on the ductility, so the relationship between the concrete strength and axial load ratio limits were proposed. Finally, the N-M interaction curves were calculated using the modified plastic stress distribution method, considering the improvement of concrete strength resulting from the confinement of steel tube and diagonal ribs. The calculated curves agree well with the test and finite element results.
