Study of Uniaxial Compression and Toughness Behavior of High Strength Steel Fiber Reinforced Concrete Columns

為了承受高樓建築於底層柱產生的高軸力，使用高強度混凝土於柱構件中具有降低斷面尺寸、降低材料用量、減少成本以及增加使用空間等優點，然而高強度混凝土的脆性破壞行為是其在應用上需要克服之處。當今多以增加鋼筋量的方式提升柱構件的韌性，卻容易導致鋼筋配置過於緊密使得施工作業困難。另外，高強度鋼筋混凝土柱一般呈現的早期保護層剝落現象，亦無法透過增加鋼筋量來改善。 於高強度混凝土中添加適量的鋼纖維可大幅改善脆性破壞行為，應用於柱構件中可紓解緊密鋼筋配置情形以及抑制保護層剝落。本研究主要探討鋼纖維應用於高強度鋼筋混凝土柱中，對於柱軸向強度以及韌性行為的影響。施作不同箍筋間距之柱試體且搭配不同鋼纖維添加量，透過柱軸壓試驗對鋼纖維之影響予以量化，其中包含圍束效應及韌性比的分析。柱軸壓試驗結果發現鋼纖維提升了高強度鋼筋混凝土柱之軸向強度及韌性行為，即便在箍筋間距放大至規範要求間距的四倍，柱試體的軸壓行為表現仍十分良好，顯示鋼纖維提供足夠的圍束效果，確實能達到紓解緊密鋼筋的目的。鋼纖維亦影響柱試體的破壞模式，表現出抑制保護層剝落、延緩主筋挫曲、均勻強度發展等特性。 本研究蒐集相關試驗結果，回歸出高強度鋼纖維鋼筋混凝土柱的韌性比預測公式，並以軸壓試驗角度，提出決定合適之鋼纖維添加量的設計流程，作為設計鋼纖維鋼筋混凝土柱時的簡易參考。同時透過OpenSEES柱軸壓試驗模型的建立與驗證，有助於快速獲得高強度鋼纖維鋼筋混凝土柱的軸壓行為。High strength concrete has been widely used since member section can be further reduced; however, its nature of brittle may become an obstacle for further application, particularly for members under high axial loading level. While requiring more lateral reinforcement may cause construction difficulty, addition of fibers can be an alternative to enhance the ductility of high strength reinforced concrete columns. This study presents the improvement of compressive strength and toughness behavior of high strength RC columns by adding high tensile strength hooked steel fibers. Eight 400×400×1200mm high strength RC columns with different stirrups spacing and fiber volume fraction were subjected uniaxial compression loading to verify the confinement efficiency. The test results show that great deformation capacity is developed even stirrups spacing is increased to d/2 in high strength RC with 1.5% fiber volume fraction. The feasibility of steel fibers as a substitute for transverse reinforcement is further confirmed. From the column failure mode, the ability to prevent the spalling and resist the buckling of longitudinal reinforcement due to addition of fibers is also observed. In terms of analysis, this study collects relevant column compression test result and conducts the toughness ratio prediction formula of high strength steel fiber RC columns by regression. The column compression test results are verified by OpenSEES model with well accuracy. A systematic design procedure to determine the appropriate amount of steel fiber in high strength RC columns is provided. Addition of high strength hooked steel fibers in high strength RC columns offers opportunities to significantly simplify the design and construction of columns, while ensuring adequate ductility and damage tolerance