高強度鋼纖維混凝土深梁剪力行為研究

Shear Behavior of High Strength Steel Fiber Reinforced Concrete Deep Beams

陳韋丞(Wei-Cheng Chen)

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(2018年)

https://doi.org/10.6342/NTU201802974

摘要

近年來高強度材料已逐漸發展成熟，如日本New RC Project，使用高強度材料可以同時縮減斷面尺寸及節省材料用量。然而伴隨著高強度混凝土的缺點是，當材料達極限強度後會發生脆性破壞，因此在使用高強度混凝土時會有安全的疑慮，因此透過添加鋼纖維於高強度混凝土中，可以解決上述之問題。
深梁在結構系統中已被廣泛地使用，然而深梁屬於應力集中之D區，而大多數D區的破壞模式易傾向脆性的剪力破壞。因此使用高強度材料於深梁中的剪力行為應深入探討。本研究使用鋼纖維混凝土澆置深梁，嘗試解決脆性的剪力破壞，並探討鋼纖維對於試體韌性及剪力強度的貢獻。
實驗計畫參照過去相關研究，以鋼纖維取代率(0.75%、1.5%)及橫向鋼筋率(0.0%~1.0%)的搭配，設計10組不同配置的深梁，進行3點不對稱抗彎試驗。其中2組試體與實驗對照組比較，設計撓曲破壞，探討透過添加0.75%鋼纖維轉變其破壞模式。另外8組試體以剪力破壞進行設計，藉此得到深梁的極限剪力強度，釐清鋼纖維於不連續區域D區之貢獻。
由實驗結果發現，添加0.75%體積取代率之鋼纖維，試體由原本的剪力破壞轉變成撓剪破壞，且在達極限強度後的力量位移曲線上，試體仍保有韌性行為。而設計剪力破壞之試體，添加0.75%與1.5%鋼纖維試體之極限剪力強度與軟化壓拉桿公式比較分別可以提升42%與72%。
另外，本研究透過分析不同鋼纖維體積取代率之試體，提出鋼纖維在剪力元素區內作用可視為一均勻的拉桿。也透過實驗結果修正鋼纖維軟化壓拉桿模型，其強度預測模型更貼近實際深梁受剪行為，且修正後模型之位移預測，其結果皆比ASCE/SEI 41-13的預測結果精確。

關鍵字

鋼纖維 ； 深梁 ； New RC ； 軟化壓拉桿 ； 剪力強度

並列摘要

Development and application of high strength materials have been facilitated either in research and practice. The New RC Project conducted by Japan is a success by using high strength concrete along with high strength rebars to reduce the member section sizes and save materials consumption. However, the brittle failure patterns owning to the nature of high strength concrete could be a major concern. Except providing more transverse reinforcement to ensure the member ductility, addition of steel fibers could be an effective alternative.
Deep beams, identified as D-region, are widely used in structures. The performance of deep beams made of high strength materials, even with steel fibers, shall be further explored. The objective of this research is to investigate the shear behaviors, to modify the softened strut-and-tie model, and to propose a force-displacement relationship of high strength fiber reinforced deep beams. The experimental program involves ten specimens were fabricated with different volume fractions of steel fiber (0.75%, 1.5%) and different transverse longitudinal reinforcement ratios (0.0%~1.0%).
The test results show that the failure mode can be transferred from shear failure to flexural failure by adding 0.75% volume fraction of steel fibers. Additionally, the ultimate shear strength can be increased by 42% and 72% by adding 0.75% and 1.50% fibers, compared to softened strut-and-tie model, respectively. It is also worth mentioning that the post peak responses are more ductile even under large deformations. By observing the strain field of the shear element, the tensile strength provided by steel fibers could be deemed as equivalent tie in the softened strut-and-tie model and the strain limitations should be modified accordingly. Finally, the force-displacement relationship of high strength fiber reinforced deep beams proposed by this study gives more accurate predictions on responses compared those obtained by ASCE/SEI 41-13.

並列關鍵字

steel fiber ； deep beam ； New RC ； softened strut-and-tie model ； shear strength

參考文獻

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