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Research on Long-Term Performance of High-Strength Self-Compacting Concrete-Filled Steel Tubes at Early Age
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摘要: 钢管高强自密实混凝土是在钢管内填入高强自密实混凝土并掺入优质膨胀剂形成的高性能组合构件，已成为大型钢管混凝土结构的发展方向。由于长期变形会加剧竖向构件的变形，随着竖向构件的变形差异和差异的逐渐累积，会引起水平构件的附加应力，甚至会导致建筑倾斜及影响正常使用功能。但针对钢管高强自密实混凝土的早龄期加载对于长期性能影响的研究十分有限。为此，进行了8组16个圆钢管高强自密实混凝土短柱长期变形的试验研究，混凝土应力水平为0.3，持荷时间为90 d。考察混凝土强度等级（C60、C80）以及加载龄期（3，7，14，32 d）对钢管高强自密实混凝土长期性能的影响。另外，进行了钢管高强自密实混凝土数值分析，基于修正后适合于添加矿物掺合料的自密实混凝土的EC2收缩徐变模型，采用逐步积分法分析粉煤灰含量、硅灰含量对钢管高强自密实混凝土长期变形的影响。试验结果表明：C60试件徐变随加载龄期的延后先增大后减小，C80试件徐变随加载龄期延后逐渐减小。参数分析结果表明：构件长期变形在单掺条件下，随着粉煤灰含量和硅灰含量增大而增大；在复掺条件下，晚龄期加载时，随着粉煤灰含量和硅灰含量增大而减小。Abstract: High-strength self-compacting concrete-filled steel tube is a high-performance composite component formed by filling high-strength self-compacting concrete into steel tubes and adding a high-quality expansion agent. It has become a development trend for large-scale CFST structures. Long-term deformation will aggravate the deformation of vertical members. Owing to the inconsistent deformation of vertical members and the gradual accumulation of such differences， additional internal forces may arise in horizontal members， which may even cause structural tilting and affect the normal service function of the building. However， research on the influence of early-age loading on the long-term performance of high-strength self-compacting concrete-filled steel tubes is very limited. Therefore， in this paper， long-term deformation tests were conducted on 16 circular high-strength self-compacting concrete-filled steel tube short columns， divided into 8 groups. The concrete stress level was 0.3， and the loading duration was 90 days. The effects of concrete strength （C60， C80） and loading age （3 d， 7 d， 14 d， 32 d） on the long-term performance were investigated. Numerical analysis was also performed on high-strength self-compacting concrete-filled steel tubes： based on the modified EC2 shrinkage and creep model for self-compacting concrete with mineral admixtures， the effects of fly ash content and silica fume content on the long-term deformation were analyzed using the step-by-step integration method. The test results showed that the creep of C60 specimens first increased and then decreased with the increase of loading age， while the creep of C80 specimens gradually decreased with the increase of loading age. The parameter analysis results indicated that under single-admixture conditions， the long-term deformation of the members increased with the increase of fly ash content and silica fume content； under composite-admixture conditions， during the late-age loading stage， the long-term deformation decreased with the increase of fly ash content and silica fume content.
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