Flexural Performance of PP-ECC Beams under Coupling of Freeze-Thaw Cycles and Bending Loads
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摘要:
为探究冻融以及冻融-弯曲荷载耦合作用对聚丙烯纤维水泥基复合材料（PP-ECC）梁抗弯性能的影响，设置7种试验工况，采用三分点加载方式对PP-ECC梁抗弯性能进行研究，分析冻融及冻融-弯曲荷载耦合作用下PP-ECC梁的荷载-跨中挠度曲线、抗弯承载力及裂缝发展形态差异；基于计算假定和正常环境下PP-ECC梁抗弯承载力的计算模型，结合PP-ECC材料冻融劣化机理，推导出PP-ECC梁在冻融环境下抗弯承载力计算模型；在此基础上引入持荷损伤系数γ，建立冻融-弯曲荷载耦合作用下PP-ECC梁抗弯承载力计算模型. 研究结果表明：不同持荷比的PP-ECC梁极限抗弯承载力在冻融循环作用下出现不同程度降低，500次冻融循环后，持荷比为0、0.25、0.50的PP-ECC梁极限抗弯承载力分别降低了28.70%、27.09%，35.69%；受拉区PP-ECC材料开裂后不退出工作仍能协同受拉钢筋参与全截面受力；PP-ECC 梁在达到极限状态时，受拉区呈多条裂缝稳态发展模式，且随冻融损伤加剧，梁体最大裂缝宽度增大、裂缝数量减少；单一冻融以及冻融-弯曲荷载耦合作用下的PP-ECC梁仍满足平截面假定；基于平截面假定建立的冻融和冻融-弯曲荷载耦合作用下PP-ECC 梁的抗弯承载力计算模型吻合度分别到达0.88～1.06和0.96～1.10.
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关键词:
- 冻融-弯曲荷载耦合作用 /
- 抗弯性能 /
- 聚丙烯纤维水泥基复合材料 /
- 抗弯承载力 /
- 多裂缝发展
Abstract:To investigate the effect of freeze-thaw cycles and coupling of freeze-thaw cycles and bending loads on the flexural performance of polypropylene fiber cement-based composite (PP-ECC) beams, seven experimental working conditions were set up. In addition, the three-point loading method was adopted to explore the flexural performance of PP-ECC beams. The differences in load-span deflection curves, flexural bearing capacity, and crack development patterns of PP-ECC beams under coupling of freeze-thaw cycles and bending loads were analyzed. Based on the calculation assumptions and the calculation model of the flexural bearing capacity of PP-ECC beams under normal environments, combined with the freeze-thaw deterioration mechanism of PP-ECC materials, the calculation model of flexural bearing capacity of PP-ECC beams under freeze-thaw environments was deduced. Furthermore, the load-bearing damage coefficient γ was introduced on this basis. The calculation model of the flexural bearing capacity of PP-ECC beams under the coupling of freeze-thaw cycles and bending loads was established. The research results show that the ultimate flexural bearing capacity of PP-ECC beams with different load-bearing ratios decreases to varying degrees under freeze-thaw cycles. After 500 freeze-thaw cycles, the ultimate flexural bearing capacity of PP-ECC beams with load-bearing ratios of 0, 0.25, and 0.5 decreases by 28.70%, 27.09%, and 35.69%, respectively. After cracking under tension, the PE-ECC material can still work with the rebar under tension and participate in the stress of the whole section. When the PP-ECC beam reaches the limit state, the zone under tension develops steadily with multiple cracks. With the aggravation of freeze-thaw damage, the width of the largest crack in the beam body increases, and the number of cracks decreases. The PP-ECC beam subjected to freeze-thaw cycles and coupling of freeze-thaw cycles and bending loads still satisfies the plane section assumption. The coincidence degree of the flexural bearing capacity calculation models of PP-ECC beams under freeze-thaw cycles and coupling of freeze-thaw cycles and bending loads established based on the plane section assumption reaches 0.88–1.06 and 0.96–1.10, respectively.
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图 5 应变片布置图
1—荷载传感器；2—分配工装；3—PP—ECC梁侧面；4—铰支座；5—应变片；6—百分表；7—PP-ECC梁顶面.
Figure 5. Strain gauge layout
图 9 冻融过程中PP-ECC的极限压缩性能变化
Figure 9. Changes in ultimate compression performance of PP-ECC during freeze-thaw process
图 10 冻融过程中PP-ECC的拉伸性能变化
Figure 10. Changes in tensile properties of PP-ECC during freeze-thaw process
表 1 PP-ECC梁具体试验参数
Table 1. Specific test parameters of PP-ECC beam
试验梁
分组试件编号 冻融循环
次数/次弯曲
荷载/%抗弯性能
试验第Ⅰ组 E0-0 0 无 是 第Ⅱ组 E0-300 300 无 E0-500 500 第Ⅲ组 E0.25-300 300 25 E0.25-500 500 第Ⅳ组 E0.5-300 300 50 E0.5-500 500 
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表 2 钢筋性能指标
Table 2. Rebar performance index
型号 直径/
mm截面面
积/mm2屈服强
度/MPa极限强
度/MPa弹性模
量/GPaQ235 6 28.26 236 390 196 HRB400 6 28.26 406 576 197 HRB400 10 78.5 411 535 203
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表 4 PP-ECC梁四点弯曲试验结果
Table 4. Four-point bending test results of PP-ECC beam
试件编号 屈服荷载/kN 极限荷载/kN 极限抗弯承载力/（kN·m） 裂缝最大宽度/mm 最终裂缝数量/条 E0-0 33.95 33.97 5.10 0.90 36 E0-300 29.34 28.84 4.33 1.10 30 E0-500 24.82 24.22 3.63 1.34 25 E0.25-300 30.88 30.72 4.61 1.25 32 E0.25-500 24.64 25.02 3.75 1.42 29 E0.5-300 26.67 26.01 3.90 1.55 23 E0.5-500 21.21 21.87 3.28 1.80 18
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表 5 PP-ECC材料本构参数
Table 5. Constitutive parameters of PP-ECC materials
PP-ECC单轴拉伸本构参数 单轴受压本构参数 σtc/MPa εtc/% σtu/MPa εtu/% σcu/MPa εcu/% 0.86 0.088 2.33 3.789 31.65 0.38
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表 6 抗弯承载力对比
Table 6. Comparison of flexural bearing capacity
冻融循环
次数/次抗弯承载力 计算值/
试验值计算值/
（kN·m）试验值/
（kN·m）0 4.50 5.10 0.88 300 4.18 4.33 0.97 500 3.88 3.63 1.06
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表 7 抗弯承载力对比
Table 7. Comparison of flexural bearing capacity
冻融循环
次数/次持荷比 抗弯承载力 计算值/
试验值计算值/
（kN·m）试验值/
（kN·m）300 0 4.18 4.33 0.97 0.25 4.46 4.61 0.97 0.50 3.75 3.90 0.96 500 0 3.88 3.63 1.07 0.25 4.14 3.75 1.10 0.50 3.48 3.28 1.06
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