Abstract Since the literature regarding the axial stiffness of concrete-filled steel tube (CFST) columns containing waste materials and their behavioral changes after thermal loading is very limited, this research attempted to evaluate the elastic modulus of rubberized fiber-reinforced concrete-filled steel tube (RuF-CFST) stub columns following thermal loading. To achieve this goal, 57 RuF-CFST specimens were constructed and various types of elastic moduli including the initial, real, secant, steel yielding point, and peak point elastic moduli were examined after thermal loading at elevated temperatures. The variables of the research for the RuF-CFST specimens with the high-strength concrete core included the thermal loading temperature (20, 250, 500, and 750 °C), percentage of crumb rubber aggregate substituting for sand by volume (0, 5, and 10%), steel fiber volume ratio (0, 1, and 1.5%), and the ratio of the steel tube external diameter to thickness (25.4 and 43). Based on the results, by increasing the thermal load, the extent of the elastic modulus drop in the specimens became notable (between 50 and 70% at 750 °C), and also, adding crumb tire to the concrete mixture led to a drop in the elastic modulus of the RuF-CFST specimens (between 7 and 18% per adding crumb tire by 10%). On the contrary, via raising the ratio of fibers in the specimens with and without thermal loading, the elastic modulus increased by 5–10%, and additionally, via raising the tube thickness, the elastic modulus increased by 25–34%. Ultimately, models to capture the elastic modulus of RuF-CFST columns after thermal loading were proposed, which were then evaluated against the empirical data of the present study and those of others, which showed a good correlation between the results.

中文翻译：

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橡胶纤维增强钢管混凝土短柱的火灾后弹性模量：实验和理论研究

摘要 由于有关含废料的钢管混凝土（CFST）柱的轴向刚度及其热载荷后行为变化的文献非常有限，本研究试图评估橡胶纤维增强钢管混凝土的弹性模量。 (RuF-CFST) 热负载后的短柱。为实现这一目标，我们构建了 57 个 RuF-CFST 试样，并在高温热加载后检查了各种类型的弹性模量，包括初始、实际、割线、钢屈服点和峰值点弹性模量。具有高强度混凝土芯的 RuF-CFST 试件的研究变量包括热加载温度（20、250、500 和 750 °C）、橡胶粒代替砂的体积百分比（0、5 , 和 10%）、钢纤维体积比（0、1 和 1.5%），以及钢管外径与厚度的比值（25.4 和 43）。根据结果​​，通过增加热负荷，试样的弹性模量下降的程度变得显着（在 750 °C 时为 50% 到 70%），而且，在混凝土混合物中添加碎屑轮胎导致了弹性模量下降。 RuF-CFST 试样的弹性模量（每增加 10% 的碎屑轮胎，弹性模量介于 7% 和 18% 之间）。相反，通过提高有和无热载荷试样中纤维的比例，弹性模量增加了 5-10%，另外，通过增加管壁厚度，弹性模量增加了 25-34%。最终，提出了用于捕获热加载后 RuF-CFST 柱的弹性模量的模型，