超高性能混凝土(UHPC)具備極高的抗壓強度與優異的耐久性，但在受壓達到極限後常呈現脆性破壞，限制了其在抗震結構中的應用。為改善UHPC的延展性，並解決傳統施工中因鋼筋密集造成的灌漿困難，本研究探討在無橫向箍筋配置下，以碳纖維(CFRP)與玻璃纖維(GFRP)複合材料管圍束 UHPC 圓柱的軸壓受力行為與破壞機制。
本研究運用Abaqus有限元素分析軟體建立三維非線性數值模型。模型中採用混凝土塑性損傷模型(CDP)模擬內部 UHPC 核心的力學行為，並結合 Hashin 損傷準則定義外部 FRP 複合材料管的破壞特徵。透過與既有文獻的軸壓實驗數據比對，驗證了此數值模型在預測構件極限承載力、應力-應變發展及破壞模式上的高度準確性。
分析結果顯示，所建立的模型能精確預測不同 FRP 層數與構件尺寸下的峰值應力，數值模擬誤差多控制在10%以內。參數分析指出，對於CFRP圍束UHPC，其側向圍束比(fl/f'c)穩定集中於 0.026。本研究進一步透過線性迴歸，針對直徑與厚度比(D/t)，提出了CFRP軟化參數(k3)的經驗公式：k3 = 0.0015 × (D/t) - 0.1148。而在 GFRP圍束UHPC的分析中，研究發現將GFRP的軟化係數定義於應變達極限應變1.005倍時，能最準確捕捉其較為脆性的破壞點。從巨觀破壞模式觀之，數值模型成功重現了FRP 因核心側向膨脹而產生的環向拉伸破裂，以及內部UHPC的嚴重壓碎現象。
本研究建立的分析框架與提出的經驗公式，能有效預測無橫向箍筋之 FRP 圍束UHPC複合構件的非線性力學行為，可為未來此類結構在工程設計與實務應用上提供可靠的數值與理論參考。

Ultra-High Performance Concrete (UHPC) possesses exceptionally high compressive strength and durability, but its application in seismic structures is often limited by its brittle failure mode under compression. To enhance the ductility of UHPC and alleviate the construction difficulties caused by congested reinforcement, this study investigates the axial compressive behavior and failure mechanisms of UHPC circular columns confined by carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) tubes without transverse stirrups.
A three-dimensional nonlinear finite element model was developed using Abaqus software. The Concrete Damaged Plasticity (CDP) model was adopted to simulate the mechanical behavior of the UHPC core, while the Hashin damage criteria were utilized to characterize the progressive failure of the external FRP tubes. The predictive accuracy of the numerical model regarding ultimate load-bearing capacity, stress-strain evolution, and macroscopic failure modes was thoroughly validated against existing experimental data.
The analytical results demonstrate that the proposed model accurately predicts the peak stress across various FRP layers and specimen dimensions, with numerical simulation errors generally controlled within 10%. Parametric analyses revealed that the lateral confinement ratio (fl/f'c) for CFRP-confined UHPC remains stable at approximately 0.026. Furthermore, based on linear regression, an empirical formula for the CFRP softening parameter (k3) was proposed as a function of the diameter-to-thickness ratio (D/t): k3 = 0.0015 × (D/t) - 0.1148. For GFRP-confined UHPC, the study found that defining the softening coefficient k3 at 1.005 times the ultimate strain accurately captures its more brittle failure point. Macroscopically, the numerical model successfully reproduced the hoop tensile rupture of the FRP jacket caused by the lateral dilation of the core, as well as the severe compressive crushing of the internal UHPC.
The analytical framework and empirical formulas established in this study effectively predict the nonlinear mechanical behavior of FRP-confined UHPC composite members without transverse stirrups, providing a reliable numerical and theoretical reference for future engineering design and practical applications.

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