Abstract Modern building codes do not cover the use of ultra-high strength concrete (UHSC) in design of composite columns. This paper investigates the structural fire performance of UHSC filled steel tubular (CFST) columns. Experimental studies were carried out on 9 CFST columns with C170/185 concrete under standard ISO fire. The columns were subjected to concentrated or eccentric compressions and then heated to failure to record the fire resistance time. The simple calculation model in EC 4 was examined by predicting the fire resistance time and comparing them with the test results; the axial force–moment (N-M) interaction strength model for room temperature design was extended to predict the fire resistance. The test results showed that the CFST columns with UHSC exhibited similar fire performance to those with normal/high strength concrete with respect to thermal expansion, axial contraction and failure modes. Adding 0.1% polypropylene fibers in UHSC was found to be effective in preventing explosive spalling especially when it was heated rapidly under the standard fire. The N-M interaction strength model gave better predictions than the EC 4 model as it gave less scattered results when compared to the test data. EC 4 buckling curve “c” was found to be conservative in predicting the fire resistance time of CFST columns with UHSC subjected to pure compression. Parametric study showed that the fire resistance of CFST columns with UHSC reduced faster than those with normal strength concrete (NSC) and high strength concrete (HSC) in early stage of heating but slower at the later heating stage. Within the practical range of load level (i.e.,≤0.7), the CFST columns with UHSC employed by this study had better fire resistance than those columns infilled with NSC and HSC.

中文翻译：

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C170/185超高强混凝土填充圆钢管火灾屈曲行为

摘要 现代建筑规范不包括超高强度混凝土 (UHSC) 在复合柱设计中的使用。本文研究了 UHSC 填充钢管 (CFST) 柱的结构防火性能。在标准 ISO 火下对 9 个具有 C170/185 混凝土的 CFST 柱进行了实验研究。柱子受到集中或偏心压缩，然后加热到不能记录耐火时间。通过预测耐火时间并将其与试验结果进行比较，检验了EC 4中的简单计算模型；用于室温设计的轴向力-力矩 (NM) 相互作用强度模型扩展到预测耐火性。试验结果表明，在热膨胀、轴向收缩和破坏模式方面，具有 UHSC 的 CFST 柱表现出与普通/高强度混凝土相似的防火性能。研究发现在 UHSC 中添加 0.1% 的聚丙烯纤维可有效防止爆炸性剥落，尤其是在标准火下快速加热时。NM 相互作用强度模型比 EC 4 模型给出了更好的预测，因为与测试数据相比，它给出了更少的分散结果。发现 EC 4 屈曲曲线“c”在预测具有 UHSC 的 CFST 柱在纯压缩下的耐火时间方面是保守的。参数研究表明，与普通强度混凝土（NSC）和高强度混凝土（HSC）相比，UHSC CFST柱的耐火性能在加热早期降低得更快，但在加热后期降低得更慢。在实际载荷水平范围内（即≤0.7），本研究采用的带有 UHSC 的 CFST 柱比那些填充有 NSC 和 HSC 的柱具有更好的耐火性。