制作PCCP的玄武岩纤维复合筋弯曲抗拉性能试验研究

Experimental study on the tensile performances with bending of BFRP Bars for PCCP

  • 摘要: 玄武岩纤维增强复合材料(Basalt Fiber Reinforced Polymer,BFRP)具有轻质、高强、耐腐蚀、耐疲劳等优点,特别适用于受腐蚀环境因素影响较大的结构工程。预应力钢筒混凝土管(Prestressed Concrete Cylinder Pipe,PCCP)是一种优秀的引调水工程管材,为解决因钢丝腐蚀和氢脆导致的断丝风险,从根本上提升PCCP安全性和耐久性,提出采用BFRP筋代替高强钢丝制作新型PCCP并开展研究。通过开展BFRP筋不同弯曲直径下的抗拉强度试验,分析得到BFRP筋抗拉强度退化规律,获取弯曲状态下BFRP筋抗拉强度折减系数,并基于数理统计提出该系数的经验公式。结果表明:BFRP筋弯曲状态下应力-应变关系仍保持线性关系,极限拉伸断裂属于脆性破坏;极限强度较直线状态折减明显,提出的抗拉强度折减系数公式可较准确地预测弯曲状态下BFRP筋极限抗拉强度,当弯曲直径为2.8 m时,BFRP筋弯曲抗拉强度较直线状态下降了22.3%,弯曲直径越大,BFRP筋强度越能得到充分利用。基于数理统计提出的抗拉强度折减系数公式可用于7 mm BFRP筋在2.2 m及以上弯曲直径状态下的极限抗拉强度计算。研究结果可为新型BPCCP结构设计提供依据。

     

    Abstract: Basalt Fiber Reinforced Polymer (BFRP) possesses advantages such as lightweight, high strength, corrosion resistance, and fatigue resistance, making it particularly suitable for structural engineering in environments significantly affected by corrosive factors. Prestressed Concrete Cylinder Pipe (PCCP) is a widely used pipeline for water diversion and regulation projects. During subterranean service, PCCP is compromised by complex soil erosion and inevitably experiences corrosion damage to its high-strength steel wire, which increases the risk of pipe failure due to broken wires and complicates project safety. To address this issue, the research team proposes replacing high-strength steel wire with BFRP reinforcement, thereby creating a new type of Basalt Fiber Reinforced Polymer Prestressed Concrete Cylinder Pipe (BPCCP) to enhance pipeline safety and durability. By conducting tensile strength tests on BFRP reinforcement with varying bending diameters, the study investigates the degradation patterns of BFRP tensile strength and determines the reduction coefficient of the tensile strength of BFRP under bending conditions. The results indicate that BFRP bars exhibit predominantly elastic deformation in a straight condition without a plastic yield plateau, and the final fracture is classified as brittle failure, with an average tensile strength of 1,274.3 MPa and an average elastic modulus of 49.3 GPa. In the bent state, the tensile stress–strain curve of BFRP bars maintains a linear relationship, and the failure mode remains brittle fracture, largely consistent with that in the straight state. Most fractures occur in a laminar manner, particularly at the same interfacial layer. The interlaminar fracture surfaces are smooth, and no significant difference in elastic modulus is observed compared with the straight condition. The ultimate tensile strength in the bent state shows a marked reduction compared with the straight state, and as the bending diameter decreases, the tensile strength of the bars is increasingly influenced by the resin properties and fiber shear capacities. Specifically, when the bending diameters are 4.0, 3.6, 3.2, 2.8, and 2.2 m, the average ultimate tensile strengths of the BFRP bars are 1,128.766, 1,098.514, 1,050.418, 990.119, and 897.999 MPa, respectively, representing a reduction of 11.42% to 29.53% compared with the straight state. The corresponding strength reduction coefficients range from 0.7047 to 0.8858, exhibiting an exponential distribution with respect to the bending diameter. For instance, with a bending diameter of 2.8 m, the bending tensile strength of the BFRP bars decreases by 22.3% compared with the straight state. As the bending diameter approaches a sufficiently large value, the tensile strength of the bars converges toward the straight ultimate tensile strength, and the strength reduction coefficient approaches 1. Theoretical analysis further indicates that applying BFRP reinforcement in a flexible state requires design based on the outer side as the control section. The stress difference between the outer side and the axis in the bending state is directly proportional to d/2R, where d represents the reinforcement diameter and R the radius of curvature. The proportionality coefficient is the elastic modulus of BFRP reinforcement. For instance, with a bending diameter of 4.0 m, when loaded to a certain stress level, the outer side experiences significantly greater strain than the mid-axis. At failure, the strain on the outer side is, on average, 857.9 microstrain higher than that at the mid-axis. The tensile strength reduction coefficient formula, proposed through statistical methods, can accurately predict the ultimate tensile strength of 7 mm BFRP reinforcement under experimental conditions with bending diameters of 2.2 m and above, thereby providing an experimental basis for the design and optimization of new BPCCP structures.

     

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