混凝土潛變及自體收縮對鋼管混凝土柱之影響研究及設計建議

Study of the Influence of Creep and Shrinkage on Concrete-Filled Steel Tubular Columns and Design Suggestions

游雅如(Ya-Ju Yu) ； 陳振川(Jenn-ChuanChern) ； 廖文正(Wen-Cheng Liao)

《結構工程》 35卷2期 (2020/06) Pp. 5-20

https://doi.org/10.6849/SE.202006_35(2).0001

摘要

鋼管混凝土柱（Concrete-filled steel tubular column，簡稱CFT柱）具高強度、高韌性，被視為具有良好耐震性能的結構構件。早期鋼管內灌混凝土是為了增加構件的側向勁度，並延緩挫曲行為的發生。近年工程師開始將核心混凝土納入實際承重單元。CFT柱受力後，混凝土潛變就會隨時間持續發展，而柱構件為了保持其斷面力平衡，混凝土會將承擔的部分軸力移轉至鋼管，這些移轉量可能會使鋼管降伏，影響結構物的安全。此外，低水膠比的高強度自充填混凝土，也會產生大量自體收縮，使構件內混凝土及鋼管間應力移轉現象愈嚴重。本研究以有限元素分析軟體ABAQUS建置三維鋼管混凝土柱模型，選擇可反映台灣混凝土特性之B4－TW潛變收縮模式，研究混凝土潛變及自體收縮引致之構件內部應力移轉的情形。模擬結果顯示，在初始鋼骨應力設定為0.6f_y的情況下，無論荷載是否偏心，考慮混凝土潛變收縮效應的最終鋼應力皆有機會超出「鋼構造建築物鋼結構設計技術規範」檢核標準。而且在使用高強度自充填混凝土及構件高寬厚比的極端情況下，鋼應力可上升0.33f_y，將大幅超過原始設計值。未來設計應注重長期荷載效應，並考量混凝土長期變形對於鋼管應力的影響。

關鍵字

鋼管混凝土 ； 潛變 ； 自體收縮 ； 應力轉移 ； B4－TW潛變收縮模式

並列摘要

Concrete-filled steel tubular (CFT) columns show not only high strength and high ductility but also exhibit favorable seismic performance. The primary intent of concrete infill is to increase lateral stiffness of member and delay the local buckling of the steel tubular. Once concrete is subjected to load, development of concrete creep begins. In order to maintain the equilibrium of forces of CFT section, part of axial load of concrete will be transferred to steel tubular which leads to the growth of steel stress. Furthermore, high strength self-consolidating concrete (SCC) with low water-to-cement ratio intensifies the rise of steel stress in CFT columns on account of high autogenous shrinkage. A three-dimensional finite element model of CFT column, which takes account of the phenomenon of concrete creep and shrinkage, is developed to evaluate stress transfer between concrete and steel in ABAQUS. B4-TWcreep and shrinkage prediction model is also applied to reflect a characteristic of high amount of paste in concrete mix designs in Taiwan owing to the soft nature of coarse aggregates. The analysis results show that under the condition of initial steel stress of 0.6f_y, the final steel stress of CFT column is probably not qualified according to ＂Design and Technique Specifications of Steel Structures for Buildings＂ owing to the long term deformation of infilled concrete whether the load is eccentric or not. In the extreme case of high concrete compressive strength of SCC and high diameter to thickness ratio, the steel stress significantly exceeds the original design value with 0.33f_y. It is suggested that relevant specifications should be revised accordingly in Taiwan.

並列關鍵字

CFT ； creep ； autogenous shrinkage ； stress transfer ； B4-TW creep and shrinkage prediction model

參考文獻

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中華民國內政部，「鋼構造建築物鋼結構設計技術規範」，台內營字第 0990807042 號(2010)。