火害後鋼骨鋼筋混凝土短柱之軸向行為

Abstract

本研究以實驗方式探討包覆十字型鋼骨鋼筋混凝土(Steel Reinforced Concrete, SRC)短柱受火害後之軸向載重行為，共設計8支SRC柱試體，其中4支柱試體為受火害之實驗組，其餘4支作為未受火害之對照組，並以斷面形狀與混凝土強度為試驗參數，將試驗分成兩個階段:(1)高溫試驗與(2)軸向載重試驗。 高溫試驗結果顯示，圓形柱之混凝土保護層較方形柱易產生爆裂行為，保護層於高溫試驗中近乎完全剝落。圓形柱因產生嚴重爆裂行為，內部溫度均較方形柱為高；混凝土強度較高之柱斷面內部溫度升溫速率較強度較低者快。此外，因包覆型SRC柱內部鋼骨高熱傳導性質之影響，SRC柱斷面溫度分佈因而不同於RC柱。 軸向載重試驗結果顯示，火害後包覆型SRC柱試體強度仍保持至少69%殘餘強度，其中圓形柱與混凝土強度較低之柱試體火害後殘餘強度較高。火害後SRC柱試體之軸向彈性剛度亦顯著下降且折減率較軸向強度為高，混凝土強度則對軸向剛度無顯著影響。火害後SRC柱試體之韌性較未受火害有所提升，其中以方形柱與混凝土強度較低之柱試體火害後之韌性較佳。最後，本研究提出火害後SRC柱殘餘強度分析方法，可準確預測試驗結果。 關鍵字:鋼骨鋼筋混凝土柱、火害、殘餘強度、斷面形狀

The study aims to investigate the axial behavior of steel reinforced concrete (SRC) stub columns after exposed to standard fire. Eight SRC small-scale columns were designed with different cross section shapes (square and circular) and concrete strengths. The experiment is divided into two parts: (1) test at elevated temperatures and (2) axial compression test. During the test at elevated temperatures, circular columns behaved seriously explosive spalling of the concrete cover, compared to the square columns with only slight corner spalling. Due to the spalling, the temperature distributions inside the circular columns were higher than those of the square columns. The columns with higher concrete strength demonstrated higher rate of temperature rise than those with lower concrete strength. Owing to the higher heat transfer property of the steel, the temperature distributions at the cross section of the SRC columns in fire were significantly different from RC columns. The test results of the axial compression test showed that the residual strength ratio of the SRC columns after exposed to fire could reach at least 69%. The residual strength of the circular columns and columns with lower concrete strength was higher. The axial elastic stiffness was considerably decreased and that was more significant than the axial strength. The effect of the concrete strength on the axial stiffness was insignificant. The ductility of specimens was increased after exposed to fire. The square columns and columns with lower concrete strength behaved more ductile. This study also proposed an analytical method to predict accurately the residual strength of SRC columns after fire.