以鋼纖維取代橫向箍筋於New RC柱之應用評估

Feasibility Study of Steel Fibers as a Substitute for Transverse Reinforcement in New RC Columns

曾笠維(Li-Wei Tseng)

指導教授 ： 廖文正

國立臺灣大學/工學院/土木工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.01955

摘要

國內的建築物中，鋼筋混凝土結構(Reinforced Concrete, RC)佔了絕大多數，主要因為RC結構有下列優點：耐久性佳、易維護，與成本低。隨著時代的演進，高樓層建築是現今的趨勢。隨著樓層的提高，位於底層的柱需承受整體結構物荷重產生的高軸力，若用傳統的RC結構，勢必得放大低樓層柱的斷面。因此日本在1988年推出為期5年的New RC Project，以提高材料強度的方法，減少材料的用量，使得結構物輕量化。高強度材料的RC結構，不僅可以降低柱斷面的尺寸、減量材料的用量與成本，也提升建築物的使用空間。
然而高強度的材料的脆性行為是其隱憂，由於高強度混凝土開裂時，裂縫會直接通過粗骨材與砂漿，因此一旦到達極限強度，結構物會立即破壞，造成嚴重的損害。除此之外，台灣位處地震發生頻繁之地震帶，結構物必須具有一定的韌性，越高的韌性越能折減地震力。為了提高結構物韌性表現，在傳統RC結構中添加新材料便是方法之一。根據文獻顯示，鋼纖維能提高混凝土材料的韌性以及剪力抗性，減少橫向箍筋量的需求，降低鋼筋籠綁紮的繁瑣。而且纖維不僅能預防早期保護層剝落，抑制裂縫生長，並會在其他部份產生多重裂縫，避免瞬間破壞的發生。
本研究主要探討在雙曲率反覆側推行為下，高強度鋼纖維鋼筋混凝土柱的行為表現，並與高強度鋼筋混凝土柱進行比較。主要分為兩大主軸，其一為「高強度混凝土與高強度鋼纖維混凝土比較」，探討相同混凝土設計強度下，一般混凝土與鋼纖維混凝土的行為差異。其二為「以鋼纖維取代橫向箍筋之評估」，以放大箍筋間距的方式，探討鋼纖維與橫向箍筋的取代關係，間距最大到規範訂定剪力鋼筋間距最嚴苛的標準，也就是一半的斷面深度。另外針對鋼筋混凝土柱以及鋼纖維鋼筋混凝土柱之韌性指數進行回歸，提出預測公式。並且根據預測公式建立圍束效應與反覆側推行為之關係式，未來具備試體設計斷面，便可以此關係式判斷反覆側推實驗結果能否通過側力衰減至80%時，層間變位角達到3%之標準。

關鍵字

鋼纖維 ； 高軸力 ； 圍束效應 ； New RC ； 反覆側推實驗

並列摘要

There are several advantages of reinforced concrete. For example, reinforced concrete is durable. Also, the buildings built by reinforced concrete are easy to conserve and maintain the structure. Moreover, the cost is low to build the buildings with reinforced concrete. It is a trend that people start to build high-rise buildings. The higher the building is, the more axial load of the columns at the bottom sustain. If the high- rise buildings are built with the traditional RC structure, the lower floors’ dimension must be enlarged. Therefore, in 1988, New RC project was proposed in Japan. The purposes of the project were increasing the strength of the construction materials and reducing the amount of the materials. With high strength material, the size of columns’ dimension is decreased, also the available space of buildings is increased.
However, the brittleness is the disadvantage of the high strength materials. Once the maximum concrete strength is reached, the construction will immediately be destroyed. Besides, Taiwan is located in a seismic belt, so the toughness is required for most of the buildings. The higher the toughness, the more it can reduce the strength caused by the earthquake. In order to increase the toughness in a traditional construction, adding new materials is one of the methods. According to the references, the toughness and the shear resistance in concrete materials are increased by adding the steel fiber into concrete. Also, the amount of the transverse steel is reduced and the process of tying steel cage is simplified. Moreover, adding the steel fiber can not only prevent the early cover spalling, but also restrain the cracks’ development that may cause immediate destruction.
The performance of high-strength steel fiber reinforced concrete columns under the condition of double curvature cyclic loading test is investigated in this study. The study can be divided into two parts. The first part is using the same designed strength to compare the differences between the original concrete and steel fiber concrete. The second part is the feasibility of substitution of the steel fiber for transverse steel based on the method that enlarging the spacing between transverse steel. Furthermore, not only the regression between the toughness of RC columns and the toughness of steel fiber RC columns was proposed in the study, but also the prediction formula. In addition, the relationship between the confinement effect that built by the prediction formula and the cyclic loading test is proposed in the study.

並列關鍵字

steel fiber ； high axial load ； confinement ； New RC ； cyclic loading test

參考文獻

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