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標題: 高強度鋼管混凝土柱強度之實驗探討
Experimental Investigation for Buckling Strength of CFT Columns with High Strength Concrete
作者: 丁英哲
Ting, Ying-Che
關鍵字: compressive member;壓力構件;CFT;composite member;鋼管混凝土;複合構件
出版社: 土木工程學系
AISC-LRFD 3rd規範針對鋼管混凝土(CFT)柱的設計觀念係採用c1、c2與c3等三個轉換係數將混凝土轉換成等值之鋼骨,再代入一般鋼柱的挫屈強度設計公式用以計算鋼管混凝土(CFT)柱之設計挫屈載重,惟LRFD 3rd 規範規定常重混凝土之抗壓強度必須介於3 ksi (21 MPa) 至8 ksi (55 MPa)之間。隨著今日科技日新月異,混凝土在抗壓強度方面有著非常顯著的提升,因此本論文希望藉由一系列純軸壓試驗探討高強度鋼管混凝土柱(8≦fc'≦12 ksi)是否仍然適用於LRFD 3rd規範。
本研究總共製作22支CFT試體柱其混凝土強度分別為fc' = 4、9、10、12 ksi,經純軸壓試驗後得其試驗強度與標稱強度之比值(Ptest / Pn),在fc' = 4、9、10、12 ksi下之平均值分別為1.43、1.46、1.54及1.59。顯示在本試驗設定之條件下,LRFD CFT公式不僅適用於高強度鋼管混凝土柱(8≦fc'≦12 ksi),而且LRFD CFT公式在計算CFT柱之軸壓強度是偏向保守的。此外由本研究之分析可知,當應變(ε)在εfc' 之前(包含ε在εfc' ),使用本研究之強度線性疊加模式去預估實際CFT柱的軸壓強度發展大致上是合理可行的,又當ε在εfc' 之後,因CFT柱本身之鋼管壁對其內部混凝土產生圍束作用,至使CFT柱的軸壓強度有著非常顯著的增加趨勢。

The AISC analysis of composite columns is done in the same way as for ordinary structural steel compression members, using the same equations from AISC Chapter E, but with values of Fy, E, and r that have been modified through the use of numerical coefficients c1, c2 and c3 . These coefficients c1, c2 and c3 are used to transform plain concrete into equivalent steel with the limitations that the compressive strength of concrete must be ranged between 3 and 8 ksi. Because the high strength of concrete has been developed in the past decade, the use of high strength of concrete is getting popular. This study is intended to see if AISC composite column formulas can still be applied through a series of axial compressive tests when the concrete strength is increased exceed the upper limit of 8 ksi.
There are 22 CFT specimens consisting of four groups with fc' = 4, 9, 10 and 12 ksi. According to the axial compressive tests, it can be concluded that the average ratios of Ptest / Pn are 1.43, 1.46, 1.54 and 1.59 for fc' = 4, 9, 10 and 12 ksi, respectively. The result shows that the LRFD formulas of high-strength CFT columns with 8≦fc'≦12 ksi is fit and the formula of calculating the buckling strength of CFT columns is also on the favor side of practicing engineers. A proposed linear superposition model also provided to predict the actual buckling strength of CFT columns. The results are quite encouraging when the strain ε is smaller than εfc' , and the compressive strength of CFT columns is in striking increase due to the confined effect of concrete in the CFT column when ε is larger than εfc'..
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