Flexural Bearing Performance of Prestressed Concrete Pipe Piles with Hybrid Reinforcement under Influence of Prestressed Control Level and Hybrid Reinforcement
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摘要:
混合配筋预应力混凝土（PRC）管桩受预应力控制水平、混合配筋等因素影响，实际抗弯承载力与理论设计值存在偏差，致使其服役过程中存在桩身破坏或性能退化等潜在风险. 为研究PRC管桩实际抗弯承载性能表现，开展不同预应力水平、混合配筋情况下PRC管桩抗弯载荷试验研究. 荷载试验采用单调连续加载方式，记录不同PRC管桩桩身弯矩-挠度曲线，确定其抗弯载荷变化规律，最终对试验所得数据与现行标准中相关弯矩承载力理论计算值进行对比验证. 研究结果表明：混合配筋方式提高了桩身承载力及延性，初始预应力张拉控制比例越高，试件的弹性变形段越长，开裂弯矩越大，裂缝出现延后，初始预应力为0.5倍张拉力时试件的延性最好，弯曲变形延性大于10，最大挠度超过54 mm，裂缝宽度为1.05～1.50 mm；PC钢棒和螺纹钢同时张拉的构件变形相对趋缓，延性和韧性更好；非预应力钢棒参与预应力贡献时，极限弯矩提高约2.5%，弹性阶段结束时的开裂挠度更大；不同预应力PRC桩开裂弯矩实测值为设计理论值的1.25～1.50倍，极限弯矩实测值为理论值的0.96～1.07倍.
Abstract:The actual flexural bearing capacity of prestressed concrete pipe piles with hybrid reinforcement (PRC pipe piles) is different from the theoretical design value due to the influence of prestressed control level and hybrid reinforcement, which leads to the potential risk of pile body damage or performance degradation during its service. In order to study the actual flexural bearing capacity of PRC pipe piles, the flexural load test of PRC pipe piles under different prestressed levels and hybrid reinforcement was carried out. The monotone continuous loading method was adopted in the load test. The bending moment-deflection curves of different PRC pipe piles were recorded to determine the flexural load variation rule. Finally, the experimental data were compared with the theoretical calculation value of relevant bending moment bearing capacity in current standards. The results show that the deformation of the hybrid reinforcement method improves the bearing capacity and ductility of the pile body. A higher initial prestress-to-tension control ratio indicates a longer elastic deformation section of the specimen, a larger cracking moment, and a delay in crack occurrence. When the initial prestress is 0.5 times the tensile force, the ductility of the specimen is the best; the bending deformation ductility is greater than 10; the maximum deflection is more than 54 mm, and the crack width is 1.05–1.5 mm. The member deformation under simultaneous tension of steel bars for prestressed concrete (PC steel bar) and screw-thread steel is relatively slow, and ductility and toughness are better. When the non-prestressed steel bars contribute to the prestress, the ultimate bending moment is increased by about 2.5%, and the cracking deflection at the end of the elastic stage is larger. The measured cracking moment of different PRC pipe piles is 1.25–1.50 times the design theoretical value, and the measured ultimate bending moment is 0.96–1.07 times the theoretical value.
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图 3 不同初始预应力工况下PRC桩跨中弯矩-挠度曲线
Figure 3. Bending moment-deflection curve in midspan of PRC pipe piles under initial prestress condition
图 4 PRC4及PRC5桩跨中弯矩-挠度曲线
Figure 4. Bending moment-deflection curves in midspan of PRC4 and PRC5 pipe piles
图 5 抗弯承载力与挠度关系曲线
Figure 5. Relationship between flexural bearing capacity and deflection
表 1 试件基本情况
Table 1. Specimen basic information
试件编号 外径/mm 壁厚/mm 长度/mm 张拉控制比例 非预应力钢筋贡献 PRC1 500 100 9 000 0.3 有 PRC2 0.5 有 PRC3 0.7 有 PRC4 0.5 无 PRC5 0.5 有 
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表 2 桩身裂缝及弯曲延性情况统计
Table 2. Statistics of pile body cracks and ductility
桩身编号 裂缝数量/根 最大裂缝宽度/mm 延性系数 μ PRC1 25 0.90 6.8 PRC2 22 0.95 8.5 PRC3 18 0.75 5.5 PRC4 27 1.05 10.6 PRC5 27 1.50 13.6
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表 3 开裂弯矩理论与实测值对比结果
Table 3. Comparison of theoretical and measured cracking moments
桩身编号 初始预应力比例 理论值（KN·m） 实测值（KN·m） 实测值/计算值 PRC1 0.3 98.1 146.5 1.50 PRC2 0.5 121.6 154.5 1.28 PRC3 0.7 145.2 181.6 1.25 PRC4 0.5 119.3 149.3 1.39 PRC5 0.5 119.3 149.5 1.37
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表 4 极限弯矩理论与实测比较
Table 4. Comparison of theoretical and measured ultimate bending moments
构件 初始预应力比例 实测值/
（KN·m）理论值 1/
（KN·m）理论值 2/
（KN·m）PRC1 0.3 355 310 354 PRC2 0.5 375 320 360 PRC3 0.7 349.5 330 363 PRC4 0.5 420.2 307 392 PRC5 0.5 409.8 307 392
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