超高性能混凝土(ultra-high performance concrete,UHPC)具備高力學性能、高韌性、高耐久性，可被運用在抗爆及抗衝擊的結構物系統或高腐蝕性的環境。在超高性能混凝土中加入鋼纖維可有效提升混凝土整體工作性，然而當混凝土開裂後，裂縫發展的過程中鋼纖維和混凝土間會產生握裹滑脫(debond)的情況，而使鋼纖維的力學特性無法發揮，良好的界面黏結力可發揮兩者的優點及性能，因此為了提升超高性能混凝土與鋼纖維間的界面黏結強度(bond strength)，兩者的介面特性需要透過纖維拉拔試驗被更深入的探討。

本論文以有限元素軟體Ls-Dyna模擬直纖維、弓形纖維、螺旋纖維在超高性能混凝土中的拉拔行為，首先針對混凝土塑性損傷模型提出校正步驟，以準確模擬超高性能混凝土在拉拔過程中的受力行為，並將拉拔試驗模擬結果理論模型以及實驗結果做比較以驗證分析的可靠性。在本論文中探討纖維在各種不同狀況下對拉拔行為的影響，包括不同的埋置角度、基材強度、纖維直徑、弓形纖維端勾幾何以及螺旋纖維斷面幾何，探討理論模型並做出適當的修正。

研究結果顯示，直徑0.38 mm弓形纖維的等效黏結強度為37 MPa約是0.2 mm直纖維的三倍(10.6 MPa)，且為直徑0.38 mm直纖維的五倍(7.2 MPa)，螺旋纖維則為 43.3 Mpa。纖維埋置於超高性能混凝土的拉拔力將隨埋置角度的增加而上升；混凝土基材強度提高，將使纖維與混凝土間的黏結強度增強，本論文亦針對直纖維在不同混凝土強度中等效黏結強度的變化，回歸一方程式以預測混凝土強度與等效黏結強度之間的關係；而弓形纖維的端勾幾何對纖維的拉拔有決定性影響，透過模擬不同端勾長度比與拉拔力、等效黏結強度間的關係，結論出當弓形纖維第一直線段與第二直線段比值為4.2時最符合經濟效應；螺旋纖維的斷面幾何對其拉拔行為影響巨大，正方形斷面纖維的拉拔性質優於三角形及矩形斷面；矩形斷面長寬比越小，等效黏結強度越大。

Ultra-high performance concrete (UHPC) is widely used in structures subjected to impact and blast loading, due to its high compressive strength, superior ductility and extraordinary durability than ordinary concrete. It can effectively improve the workability of ultra-high performance concrete by adding steel fibers in to UHPC. However, the propagation of crack would cause the interface of concrete and steel to debond. In order to improve the interfacial bond strength, it is important to make a further investigation over the characteristics of the interface of ultra-high performance concrete and steel fiber.

In the thesis, finite element models were developed to simulate the pullout behavior of smooth fiber, hooked-end fiber, and twisted fiber from the ultra-high performance concrete by finite element analysis software Ls-Dyna. At the beginning, we modified the concrete damage model in order to simulate the properties of ultra-high performance concrete in the single fiber pullout experiment more accurately. Then we compare the result of simulate analysis with the experiment data to ensure the reliability of the simulation. We also investigate the influence of the fiber inclined angle, compressive strength of concrete, diameter of steel fiber, geometry of hooked-end and the cross section of twisted fiber to the pullout behavior of steel fiber.

The report shows that the equivalent bond strength of hooked-end fiber is 37 MPa, which is three times of the equivalent bond strength of smooth fiber. Furthermore, the equivalent bond strength of twisted fiber is 43.3 MPa is about four times of the bond strength of the smooth fiber. Also, the pullout load would increase with an increase in the angle of fiber inclination. In the thesis, we also proposed an equation to investigate the relationship between compressive strength of concrete and the equivalent bond strength. Considering the influence of geometries of hooked end, we concluded that the ratio of the 1st and 2nd straight section equals to 4.2 is the most effective value to have a better pullout response of hooked end steel fiber. And the equivalent bond strength of twisted fiber with triangular cross section is better than that of square and rectangular.

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