斜拉肋加劲薄壁方钢管混凝土柱的滞回性能研究

在方钢管两临边焊接斜拉肋可显著提高薄壁方钢管的局部屈曲承载力,有效改善薄壁方钢管混凝土(CFST)柱的力学性能。为研究斜拉肋加劲薄壁方CFST柱的滞回性能,完成4个试件的拟静力试验。试验主要变化参数为斜拉肋上是否开孔、轴压比、钢管宽厚比。试验结果表明:试件的破坏模式为压弯破坏,破坏区域钢板受压鼓曲、钢管与斜拉肋之间纵向焊缝断裂、混凝土压溃;试件滞回曲线稳定饱满,无明显捏拢现象;试件破坏时位移延性系数均大于3.3,极限层间位移角均大于1/30;斜拉肋上开孔对试件的性能影响不明显,减小钢管宽厚比或者增加轴压比使试件耗能增大,但变形能力下降。应变分析结果表明:斜拉肋加劲方钢能对混凝土提供较均匀约束,并且斜拉肋与钢管之间能协同工作。基于ABAQUS软件建立的精细有限元模型能较准确地预测钢管混凝土柱在恒定轴力和反复水平力下的承载力及变形能力。参数分析表明:混凝土强度和轴压比明显影响试件的变形能力,进而建议混凝土强度与轴压比限值的关系。提出考虑斜拉肋和钢管约束之后的塑性应力分布方法计算N-M曲线,与试验结果和有限元分析结果吻合良好。

Hysteretic behavior of square thin-walled CFST column stiffened by diagonal ribs

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.