彎矩構架合成梁於火害中之行為

Abstract

本研究藉由耐火試驗探討彎矩構架合成梁於火害中之行為，同時利用理論計算方式，計算試驗中無法取得之合成梁軸力變化。耐火試驗規劃兩組試體，探討束制柱斷面尺寸對試體行為之影響。試驗結果顯示，試體受火梁因高溫導致材料強度折減，受火梁撓度隨溫度增加而逐漸增大；受火梁軸向變形亦因高溫影響產生熱膨脹，由於柱構件束制，使受火梁承受軸壓力而產生梁腹板及下翼板之局部挫屈；束制柱之斷面大，則束制勁度大，對受火梁熱膨脹之約束也較大，使受火梁達到最大軸向伸長量之時間較早，且能達到之最大軸向伸長量較小，但局部挫屈行為較為明顯。束制柱之斷面大，能略微提升試體之防火時效。理論計算結果顯示，束制柱之斷面越大，升溫初期熱膨脹造成之軸壓力上升較快，理論計算方式能夠合理預測合成梁軸壓力隨時間變化之趨勢。

This study has been conducted experimentally to investigate the behavior of composite beams in moment frames at elevated temperatures and theoretically to evaluate the axial forces within the composite beams. Two specimens were tested to study the effects of the restraint stiffness of the composite beam which provided by different column sizes. Test results demonstrated that the deflection of the composite beams gradually increased due to the deterioration of the material strength at elevated temperatures. When composite beams are subjected to fire, thermal expansion of the composite beams is restrained and compression force is produced, resulting in local buckling at the lower flange and web of the composite beams. For the specimen with larger column section, the maximum axial deformation was reached earlier and the maximum axial deformation was smaller, but the local buckling behavior was more obvious. In addition, it had better fire resistance than the specimen with smaller column section. The theoretical calculation results demonstrated that the compression forces in the specimen with larger column section had a faster increasing rate at the beginning of the test, and local buckling behavior occurred earlier. The theoretical calculation in this study can reasonably predict the axial forces of the composite beams in moment frames.