火害下剪力釘於合成梁及柱之力學行為

Abstract

本研究以有限元素分析探討火害下剪力釘於合成梁及柱之力學行為。於箱型鋼柱內灌混凝土之合成柱，分析有無配置剪力釘於承受柱極限載重30%或60%之軸向載重於標準升溫之行為。合成梁則以分析剪力釘於預定溫度下之極限強度，探討混凝土強度、剪力釘材料強度及鋼梁溫度等參數於合成梁剪力強度之影響。合成柱之分析，於有配置剪力釘試體之斷面溫度分佈圖可發現剪力釘可有效傳遞熱至較內部的斷面。分析之合成柱因高溫而產生之軸向伸長變位都較試驗結果稍高，但可預測合成柱軸向變位之趨勢。於合成柱因高溫造成箱型鋼柱的橫向變形，可明顯看出配置剪力釘使箱型鋼柱橫向變形量減少，與無剪力釘合成柱之橫向變形大為不同。分析與試驗結果都顯示，火害下有配置剪力釘之合成柱較無配置剪力釘之合成柱於防火時效僅有些微之提升。合成梁經有限元素分析的參數分析結果顯示，試體溫度的升高造成混凝土及鋼材的材料強度遞減，使得剪力釘強度降低。在各溫度條件下，當剪力釘強度及混凝土強度兩者皆提高時，合成梁之剪力強度也相對提高。有限元素分析判斷分析模式破壞型式方面，於20、400及700oC時，於各混凝土及剪力釘強度條件下都為剪力釘破壞控制，不同於規範之有混凝土破壞控制。有限元素分析結果與規範Eurocode計算之火害下剪力釘強度進行比較，於預載40%情況下分析可合理預測各溫度下合成梁之剪力強度。

Finite element analyses were conducted to investigate the behavior of shear studs in composite beams and columns under fire. Analysis was performed to study the behavior for the concrete filled box steel composite columns, with or without shear studs, which subjected to axial compression of 30 or 60% of the column ultimate axial strength and standard temperature increasing. For composite beams, the strength of the shear studs under certain temperatures was analyzed. The effects of the parameters, such as concrete strength, material strength of the shear stud, and steel beam temperature, on the shear strength of the composite beam were studied. The analysis results of the composite columns showed that the shear studs could effectively transfer the heat into inside of the cross section as shown in the temperature distribution of the cross section. The axial elongations of the composite columns due to elevated temperatures from the analysis were higher than those from the test. However, the analysis could predict well the trend of the axial deformation of the composite columns. The lateral deformation of the box steel plates due to the high temperatures indicated that the shear studs would decrease the lateral deformation of the box steel plates that significantly different from the lateral deformation of the composite column without shear studs. Both the analysis and test results indicated that the fire resistance of the composite columns with shear studs was marginally better than that of the composite columns without shear studs. The results of parametric study using finite element analysis of the composite beams showed that the material strengths of the concrete and steel decreased due to the elevated temperatures and that resulted in the decrease of the shear stud strength. At various temperature conditions, the shear strength of the composite beams was increased with the increase of the material strengths of either shear stud or concrete. At various temperatures and material strengths, the composite beams failed due to the failure of the shear studs, which was different from the code prediction. The comparison of the analysis results and Eurocode calculation showed that the analysis could reasonably predict the shear strength of the composite beams under 40% preload at various temperatures. Keywords: composite column, composite beam, shear stud, in fire.