火害下內灌混凝土箱型鋼柱之軸向受力行為

Abstract

本研究以實驗方式與數值分析探討實尺寸內灌混凝土箱型鋼柱受軸壓力於火害下之行為。實驗依規範與試驗爐容量設計製作三組試體。二組試體噴附二小時防火時效之被覆。實驗時三組試體分別施加試體100%、100%、56%之工作載重，進行加熱試驗，以探討CFBC試體的耐火性能與破壞行為。噴附二小時防火被覆之試體可達二小時的防火時效。第一支試體於高溫後冷卻再進行軸向加載試驗，發現試體能恢復軸向勁度並於工作載重範圍內呈現線彈性行為。試體的高溫破壞試驗時持續有混凝土爆裂的聲音，因鋼板的圍束未導致立即的破壞，最終破壞模式為鋼板局部的鼓起與內部混凝土的碎裂。實驗顯示內灌混凝土箱型鋼柱有可接受的防火性能。更進一步建立數值分析方法，以試體之溫度歷時數據，考慮材料熱膨脹及高溫下材料力學性質之折減，以計算試體之軸向變形。結果發現分析方法可達到與試驗結果良好的吻合。

This research has been conducted experimentally and numerically to investigate the behavior of full-scale concrete-filled steel box columns (CFBCs) subjected to axial compression load and elevated temperature. Three CFBC specimens were designed and constructed according to the current design code and capacity of the furnace. Two of the specimens had been sprayed with fire protection coating for two hours fire resistance rating. During the test, axial compression, corresponding to 100%, 100% and 56%, respectively, of the nominal compression strength of the specimens, was applied to these three specimens, and the specimens were proceeded the fire test to study their behavior and failure in fire. The specimens with two hour fire protection can reach two hours fire resistance rating. For the first specimen, axial compression test was performed again after the specimen had been cooled. Within the range of the design load, the axial stiffness of the specimen was recovered and the specimen behaved linearly elastic. During the specimen tested under elevated temperature, sound of the concrete bursting was continued heard which did not cause immediate failure of the specimen due to the confinement of the column steel plate. The final failure mode was the bulge of the column steel plate and inner concrete crushing. The experimental results indicate that concrete-filled box columns possess acceptable fire resistance. Moreover, utilizing the recorded temperature on the specimens, an analytical method was established to predict the axial deformation of the specimens by considering thermal expansion and reduction of the mechanical properties of the materials at elevated temperature. As a result, analytical method can achieve good agreement with test results.