鋼骨鋼筋混凝土邊柱之火害行為

Abstract

本研究利用實驗及分析方法探討鋼骨鋼筋混凝土(Steel Reinforced Concrete, SRC)邊柱於火害下之行為。實驗方面分為兩階段：第一階段為高溫試驗，於小型複合高溫爐進行，並以熱電偶量測鋼骨、鋼筋及混凝土之升溫狀況；試驗規劃4支鋼骨鋼筋混凝土柱研究SRC邊柱於不同參數下之斷面溫度分佈，參數包括混凝土強度以及柱斷面形狀。第二階段為載重試驗，利用大型萬能試驗機進行軸壓載重試驗。高溫試驗之4支受火害試體可得到SRC柱受火害後之殘餘強度，另外4支未受火試體則可得到未受火害之軸壓強度，兩組試體對照比較後可知SRC柱試體受火害後之強度折減程度。分析部分採高溫試驗得到之試體斷面溫度分佈數據，以熱傳學塊狀系統之概念推估SRC柱試體火害後之殘餘強度，並與實驗值比較。 研究結果顯示，高溫下圓形柱受火面之混凝土保護層嚴重爆裂，反之方形柱僅於受火面角隅處混凝土剝落，可知斷面幾何形狀影響試體之耐火能力。不同強度混凝土對於斷面溫度分佈及升溫速率並無明顯影響；鋼骨腹板之溫度高於鄰近混凝土測點溫度，是由於鋼骨熱傳導係數較混凝土高，熱能傳遞過程中產生蓄熱、溫度上升情形。載重試驗之結果顯示，強度較高混凝土之柱試體殘餘強度折減程度大於普通強度混凝土之試體。殘餘剛度折減程度方面，試體參數為方形斷面及普通強度混凝土之組合，折減程度最小。韌性方面，火害後試體之韌性皆有不同程度之增加。本研究提出合理之分析方式計算受火害試體之殘餘軸壓強度，分析之結果與實驗數據相符。包覆型SRC柱由於混凝土之包覆可降低火害之影響且具優異之防火性能。

This paper employs both experimental and numerical methods to investigate the behavior of steel reinforced concrete (SRC) columns subjected to fire. The experimental work was divided into two phases. Phase one was to test four column specimens under standard fire condition and to study the temperature distribution on the cross section. Test parameters included shape of the cross section (square and circular) and concrete strength. Phase two was to conduct axial compression test of eight column specimens and to study the residual properties after expose to fire. An analytical method was developed to predict the residual strength of SRC columns subject to fire by adopting the temperature distribution data from test results. Test results show that the concrete cover of circular SRC columns severely spalled, however the spalling occurred only at corners for square columns. The concrete strength had insignificant effect on temperature distribution and rate of the temperature rise. Temperatures on the steel were higher than nearby concrete that was attributed to the heat transfer of the steel. The axial compression test results indicate that specimens with high strength concrete had greater reduction on residual strength than specimens with normal strength concrete. Specimens exposed to fire demonstrated increase of the ductility. The analytical predictions for axial residual strength agreed closely with the experimental result. Concrete encased steel SRC columns demonstrated excellent fire resistance performance due to the encase of the concrete.