內灌混凝土箱型鋼柱於火害下之行為

Abstract

本研究採用實驗方式與有限元素分析方法，探討受軸向定載內灌混凝土箱型鋼柱於火害下之構件行為與耐火性能，並依據研究成果提出內灌混凝土箱型鋼柱耐火時間公式。實驗規劃4支試體進行耐火實驗以瞭解試體斷面溫度分佈、軸向變形與破壞模式，並探討施加不同軸向載重(30%和60%試體極限強度)與有無配置剪力釘之試體參數對柱構件耐火性能的影響。有限元素分析為透過熱傳分析與考量溫度影響之非線性結構分析模擬高溫實驗試體行為，進而探討試體高溫下鋼柱與混凝土分別之變形行為與受力情況。利用數學模型採最小平方法擬合本研究與文獻實驗結果之下限值，以建立內灌混凝土箱型鋼柱耐火時間公式。 實驗結果顯示，升溫環境使內灌混凝土箱型鋼柱溫度逐漸增加，而構件溫度增加造成其先產生軸向伸長變形後，再產生壓縮變形直至破壞。破壞模式為柱壓縮破壞，試體柱鋼板多處局部挫屈變形且混凝土碎裂。試體載重比參數相較剪力釘參數明顯影響柱構件軸向變形行為與耐火時間。分析結果顯示，有限元素分析模型可合理預測試體受火害中溫度分佈與變形趨勢。分析可見試體於火害期間會產生軸向與橫向變形，亦可用以計算火害期間箱型鋼柱與混凝土各別之承載。最後，本研究提出內灌混凝土箱型鋼柱耐火時間公式，可保守且合理的預測耐火時間，期有助益於防火性能設計。

This study was conducted experimentally and numerically to explore the fire resistance of axial-loaded concrete-filled steel box columns exposed to fire. According to the test results, a fire resistance formula was proposed. Four specimens were designed and tested to study the temperature distribution on cross section, the axial deformation, and the failure mode, and to investigate the effects of load ratio (30% and 60% of the ultimate strength) and shear stud on fire resistance. Finite element analyses were performed for both heat transfer and nonlinear static analyses and used to simulate the fire behavior of the specimens, and further to explore the individual deformation and the load-carrying capacity of the steel box column and the concrete. The fire resistance formula was established by means of least squares regression to fit lower bound of the test results of this study and literature. The test results showed that the specimens axially elongated due to the temperature increase when the specimens were exposed to temperature increase. Next, the specimens turned to shortening till failure. The failure mode was the compressive failure of the column, including shortening of the specimens, bulge of column steel plate, and crushing of concrete inside the steel box. Compared to the shear stud, the load ratio highly affected the axial deformation and the fire resistance. The analytical results indicated that the analysis reasonably predicted temperature distribution on the cross section and the tendency of the axial deformation of the specimens. The analysis results also revealed that the axial and lateral deformation of the specimens subjected to fire. Moreover, the individual load-carrying capacity during the fire duration of the steel box and the concrete could be calculated. Finally, a fire resistance formula was proposed to predict the fire resistance of the concrete-filled steel square box columns. The formula can conservatively and reasonably predict fire resistance and will benefit the performance-based fire resistance design.