摘要:
圆形钢管混凝土可以充分发挥钢管和混凝土的组合作用,使得钢管混凝土承载力和延性得到明显提升,因而广泛应用于工程结构中。将高强钢应用于钢管混凝土柱,可以减小构件尺寸和自重,使结构在节省材料用量的同时获得更大的可用空间,更加经济环保。然而,现行钢管混凝土设计规范主要是依据普通钢材强度等级的研究成果制定的,对采用高强钢的钢管混凝土的适用性尚未可知。此外,针对高强钢管混凝土短柱轴压性能,现有研究主要关注其在承载时的结构性能,而很少关注钢管和内填混凝土在不同变形阶段分别承担轴力的贡献。因此,基于试验对高强钢管混凝土短柱的轴压性能展开了研究。首先,对6个短柱进行了轴压试验,包括3个钢管混凝土试件和3个纯钢管试件。主要的试验参数为钢材强度等级,包括Q355,Q460和Q690。之后,基于试验结果,分析了试件的破坏形态、荷载-位移曲线、承载力以及钢管和内填混凝土的轴力贡献。最后,探讨了现行设计规范对圆形钢管混凝土轴压短柱承载力的适用性。试验结果表明:所有纯钢管和钢管混凝土试件均表现出了良好的延性;由于混凝土的存在,钢管混凝土的承载力比纯钢管的承载力提高了30%以上。基于纯钢管和钢管混凝土的应变分析结果,分离了钢管混凝土钢管和内填混凝土的轴力贡献。结果表明:钢管提供的约束作用使得混凝土所承担的轴力明显增加,且钢材强度等级越高,混凝土轴力提高效果越明显;尽管钢管提供了横向约束作用,但其轴力贡献与其屈服承载力相比未明显折减。试验结果和规范预测结果的对比分析表明:现行中国规范GB 50936—2014《钢管混凝土结构技术规范》可以有效预测采用普通强度钢材的钢管混凝土试件的承载力,但当钢管采用高强度钢材时,规范将给出过于保守或偏于危险的预测结果;现行欧洲规范(EN 1994-1-1)中的截面承载力计算方法对采用普通钢和高强钢的钢管混凝土试件均给出了合理且偏于安全的承载力预测值,仍可以适用于Q690高强钢管混凝土,但该规范低估了钢管的轴力贡献,高估了内填混凝土的轴力贡献。
Abstract:
Circular concrete-filled steel tubes (CFSTs) can fully utilize the composite action of the steel tube and infilled-concrete, and thus its load-bearing capacity and ductility can be significantly enhanced. Therefore, they are widely used in engineering structures. The application of high-strength steel (HSS) in CFST columns can reduce the size and self-weight of the members and allows structures to achieve greater usable space while saves material, which is more economical and environmentally friendly. However, the current design codes for CFSTs are primarily based on research achievements using ordinary steel strength grades, and whether the codes are still applicable to CFSTs with high-strength steel remains unknown. In addition, existing research on the axial compression behaviour of CFST stub columns with HSS mainly focuses on the structural behaviour at the ultimate load, while little attention is given to the axial force contributions of the steel tube and the infilled concrete at different deformation stages. Therefore, this paper experimentally investigated the axial compression behaviour of CFST stub columns with HSS. Firstly, axial compression tests were conducted on six stub columns, including three CFST columns and three pure steel tubes. The main test parameter was the steel grade, including Q355, Q460, and Q690. Subsequently, based on the test results, the failure states, load-deflections, load-bearing capacity, and axial force contributions of the steel tube and infilled concrete were analysed. Finally, the applicability of the current design codes in predicting the load-bearing capacity of circular stub CFST columns under compression was discussed. The test results indicate that all the pure steel tube and CFST specimens exhibited good ductility. Due to the presence of concrete, the load-bearing capacities of CFST columns were increased by more than 30% compared to these of pure steel tubes. Based on the strain gauges attached on the surface of the steel tube, the axial resistance contributions of the steel tube and infilled concrete of CFST columns were separated. The results show that the confinement provided by the steel tube significantly increased the axial force carried by the concrete, and the increase in concrete axial force was more pronounced with higher steel grades. Although the steel tube provided lateral confinement, its axial force contribution was not significantly reduced compared to its yield load-carrying capacity. Comparative analysis between the experimental results and the predicted results by design codes reveals that the current Chinese design code (GB 50936—2014) can effectively predict the compression resistance of CFST columns using ordinary grade steel, but when high-strength steel is used for the steel tube, the code tends to provide overly conservative or potentially unsafe predictions. The current European design code (EN 1994-1-1) provides reasonable and conservative predictions of the compression resistance for CFST columns using both ordinary steel and high-strength steel. It can still be applied to CFST columns with Q690 HSS. However, EN 1994-1-1 underestimates the axial resistance contribution of the steel tube and overestimates the axial resistance contribution of the infilled concrete.
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