填充型箱型鋼柱火害中之力學行為

Abstract

本研究針對受軸向定載填充型箱型鋼柱於火害環境下，以實驗與分析方法進行柱構件耐火性能研究，耐火試驗藉由規劃三組試體，探討施加載重比、試體斷面尺寸及有無配置縱向鋼筋之影響。試驗結果顯示，試體受熱後產生軸向熱膨脹伸長，隨著試體溫度增加，試體原承載能力逐漸下降，使試體軸向變形轉為壓縮變形，直到試體破壞；試驗施加載重比對於試體軸向膨脹伸長量及耐火性能時間有顯著的影響；試體斷面尺寸會影響試體膨脹伸長量，但對於試體軸向變形行為及耐火性能時間影響較不顯著；配置縱向主筋可以延長試體耐火性能時間，但對於試體膨脹伸長變形行為則較無影響。力學分析結果發現，受熱前箱型鋼柱與混凝土初始承擔之載重與其材料性質及斷面積相關，而高溫試驗開始後箱型鋼柱因溫度上升較混凝土快及熱膨脹性質影響，導致承擔之載重逐漸增加，爾後箱型鋼柱於高溫下失去承載能力，載重又逐漸轉移回由混凝土承擔，直至箱型鋼柱與混凝土皆達破壞，分析結果可合理的預測試體軸向變形與時間的關係。本研究以實驗與分析方式建立填充型箱型鋼柱的耐火行為。

This study aims to investigate experimentally and analytically the fire resistance of concrete-filled steel box columns under axial compression and at elevated temperatures. Three specimens were tested to study the effects of the variables such as load ratio, size of the cross section, and presence of the longitudinal bars on their fire behavior. Test results demonstrated that the specimens expanded axially while the specimens were subjected to temperature increase in the early stages of fire exposure. However, the axial deformation changed from expansion to contraction while the specimens’ axial capacities gradually decreased because of further temperature increase. The magnitude of the applied axial compressive force highly affected the axial elongation and fire resistance. The size of the cross section of the specimens influenced the elongation magnitude, but had little effects on the fire resistance. Specimen with longitudinal bars had larger fire resistance than those without the longitudinal bars. The results of the analytical approach indicated that the load share of the steel section and concrete related to their material properties and cross-sectional areas before the fire test. When the specimens exposed to fire, the load share of the steel section gradually increased because the steel section expanded faster than the concrete. Next, the load share of the steel section progressively shifted back to the concrete since the steel section further lost its load-carrying capacity caused by the elevated temperatures. The specimens finally failed when both steel section and concrete reached their capacities at elevated temperatures. Analytical approach reasonably predicted the axial deformation-time relations of the specimens. The fire behavior of concrete-filled steel box columns was established experimentally and analytically in this study.