Ultra-high strength concrete has been applied in concrete encased steel column to enhance strength and reduce usage of concrete. However, there are limited specifications in current design codes on ultra-high strength concrete encased steel columns (UHSCESC), particularly for fire effects. This paper presents numerical simulation of fire behaviour of UHSCESC exposed to standard fires. A thermo-mechanical model of UHSCESC is established by considering the effect of transient thermal strain and validated against experimental results. The effect of slenderness ratio, section size, load ratio, concrete strength, steel strength, reinforcement ratio and steel ratio on the fire behaviour of UHSCESC is investigated through parametric studies. The predicted fire resistance of UHSCESC is finally compared to EC4 results. It is found that the temperature of the steel section is lower than its critical value, and the load bearing capacity of UHSCESC is almost evenly provided by the core concrete and steel section. The slenderness, section size and load ratio have significant effects on fire resistance of UHSCESC, leading to a wide range more than 300 min. The EC4 method is not applicable to UHSCESC which may provide unconservative fire resistances up to one hour and over-conservative results of nearly four hours.

超高强度混凝土已应用于混凝土包裹的钢柱中，以提高强度并减少混凝土用量。但是，当前设计规范中关于超高强度混凝土包裹钢柱（UHSCESC）的规范非常有限，特别是在防火方面。本文介绍了暴露于标准火灾下的UHSCESC火灾行为的数值模拟。考虑瞬态热应变的影响，建立了UHSCESC的热力学模型，并针对实验结果进行了验证。通过参数研究研究了细长比，截面尺寸，载荷比，混凝土强度，钢强度，增强比和钢比对UHSCESC防火性能的影响。最终将UHSCESC的预测耐火性与EC4结果进行比较。发现钢截面温度低于其临界值，并且UHSCESC的承载能力几乎由核心混凝土和钢截面均匀地提供。细长，截面尺寸和负载比对UHSCESC的耐火性有重大影响，导致300分钟以上的宽范围。EC4方法不适用于UHSCESC，UHSCESC可能提供长达一小时的非保守耐火性和近四个小时的超保守结果。