Effect of seawater wet-dry cycles on mechanical performance of RC beams with initial damage
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摘要:
沿海环境下的钢筋混凝土(RC)结构处于荷载作用和环境作用同时存在的工作状态且在正常条件下会出现不同程度的荷载损伤。为了在实验室内模拟其工作状态，对RC梁试件施加幅值分别为0.3
P u、0.4P u、0.5P u、0.6P u和0.7P u(P u为单调加载梁的极限荷载)的初始荷载造成不同程度的损伤，经历120次海水干湿循环作用后，进行单调加载试验测试剩余力学性能，并对梁试件钻芯取样测试不同位置及深度处混凝土的氯离子含量。试验结果表明，不同程度初始损伤RC梁经历120次海水干湿循环后，其屈服荷载、极限荷载和延性均随初始荷载幅值的增加而降低；与无损伤梁试件相比，当初始损伤荷载为0.4P u时，梁试件的屈服荷载和极限荷载降幅分别为10.4%和7.9%，随着初始荷载增大，屈服荷载和极限荷载快速下降，当初始损伤荷载为0.7P u时，屈服荷载和极限荷载降幅分别达33.7%和32.4%。氯离子含量测试结果表明，梁试件混凝土受拉区氯离子含量均大于受压区氯离子含量；当初始损伤荷载小于0.5P u时，受拉钢筋表面混凝土的氯离子含量差别不大且小于0.1%，当初始损伤荷载为0.7P u时, 钢筋表面氯离子含量最大达到0.14%。可见，初始荷载损伤与海水干湿循环综合作用对RC梁力学性能及耐久性劣化影响显著。-
关键词:
- 初始损伤 /
- 钢筋混凝土(RC)梁 /
- 海水干湿循环 /
- 耐久性 /
- 氯离子含量
Abstract:The working condition of reinforced concrete (RC) structures in coastal chloride environment combined load effects and environmental effects and there would be a different degree of damage due to load effects in normal conditions. In order to simulated that working condition in laboratory, different loads of 0.3
P u, 0.4P u, 0.5P u, 0.6P u and 0.7P u (P u is the ultimate load of beam under monotonic loading) were applied on RC beam specimens to induce varying degrees of damage. Subsequently, beam specimens were placed in an automatic sprinkler device to simulate seawater wet-dry cycles. After 120 wet-dry cycles, monotonic loading test and chloride concentration test were conducted on RC beams. The test results show that the yield load, ultimate load and ductility of specimens decrease with the increase of initial damage load amplitude. When the initial load is 0.4P u, the decrease of yield load and ultimate load is 10.4% and 7.9% respectively, compared with control group. With the damage increasing, the yield load and ultimate load decrease constantly. When the initial load is 0.7P u, a great degeneration of mechanical performance occurs and the decrease of yield load and ultimate load is 33.7% and 32.4% respectively. The results of chloride concentration test show that the chloride ion content of concrete in tension area is higher than that in compression area. When the initial load is below 0.5P u, the chloride ion content in steel position is below 0.1% and has no significant changes. When the initial load is 0.7P u, the chloride ion content increases significantly and the maximum value is up to 0.14%. Thus, the initial damage combined with seawater wet-dry cycles has a great impact on degradation of mechanical performance and durability of RC beams. -
图 1 钢筋混凝土梁试件几何尺寸和配筋
Figure 1. Geometry size and reinforcement of reinforced concrete beam specimen
图 3 海水干湿循环自动喷淋装置示意图
Figure 3. Schematic diagram of automatic sprinklerfor seawater wet-dry cycle
图 4 混凝土氯离子含量取样位置示意图
Figure 4. Schematic diagram of sampling position of chloride ion content in concrete
图 5 梁试件B-0.4裂缝趋势和测点位置示意图
Figure 5. Schematic diagram of cracking tendency and test point position for beam specimen B-0.4
图 7 干湿循环前后3种典型的裂缝宽度变化
Figure 7. Three typical changes of crack width before and after wet-dry cycles
图 9 极限荷载、屈服荷载及位移延性系数随初始损伤荷载的变化
Figure 9. Variation of ultimate load, yield load and displacement ductility coefficient with initial damage load
图 10 干湿循环前后梁试件抗弯刚度变化
Figure 10. Variation of bending rigidity of specimens before and after wet-dry cycles
图 11 B-0.3梁试件氯离子含量随深度变化
Figure 11. Variation of chloride ion content with depth of beam specimen B-0.3
图 12 B-0.5梁试件氯离子含量随深度变化
Figure 12. Variation of chloride ion content with depth of beam specimen B-0.5
图 13 B-0.7梁试件氯离子含量随深度变化
Figure 13. Variation of chloride ion content with depth of beam specimen B-0.7
图 14 钢筋表面氯离子含量和混凝土保护层总氯离子含量与初始损伤荷载幅值
Figure 14. Chloride ion content at reinforcement surface and total chloride ion content in concrete cover with initial damage load amplitudes
表 1 梁试件初始损伤加载幅值和试验环境
Table 1. Beam specimen initial damage load amplitude and test environment
编号 荷载幅值 试验环境 B-0 0 干湿循环 B-0.3 0.3 Pu 干湿循环 B-0.4 0.4 Pu 干湿循环 B-0.5 0.5 Pu 干湿循环 B-0.6 0.6 Pu 干湿循环 B-0.7 0.7 Pu 干湿循环 B-Ref 0 标准养护 
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表 2 干湿循环前后梁试件裂缝宽度变化统计
Table 2. Variation statistics of crack width of beam specimen before and after wet-dry cycles
编号 最大裂缝宽度/mm 干湿循环前裂缝宽度/mm 总测点数量 干湿循环后裂缝变化测点数量 完全愈合 部分愈合 基本稳定 B-0.3 0.08 < 0.1 7 5 2 0 0.1~0.2 0 0 0 0 ≥0.2 0 0 0 0 B-0.4 0.19 < 0.1 15 9 4 2 0.1~0.2 15 2 3 10 ≥0.2 0 0 0 0 B-0.5 0.34 < 0.1 15 12 2 1 0.1~0.2 17 1 4 12 ≥0.2 4 0 0 4 B-0.6 0.63 < 0.1 26 15 6 5 0.1~0.2 20 2 3 15 ≥0.2 8 0 0 8 B-0.7 1.16 < 0.1 22 15 5 2 0.1~0.2 14 0 1 13 ≥0.2 9 0 0 9
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表 3 梁试件单调加载试验结果
Table 3. Testing results of beam specimen under monotonic loading
编号 Py/kN δy/mm Pm/kN δm/mm δu/mm δu/δy B-0 41.09 2.06 50.50 17.37 37.82 18.4 B-0.3 38.05 2.85 47.48 26.31 33.11 11.6 B-0.4 36.81 2.75 46.51 31.23 36.25 13.2 B-0.5 33.03 2.56 41.99 20.56 26.89 10.5 B-0.6 27.32 2.27 38.79 17.54 17.81 7.8 B-0.7 27.25 2.33 34.14 18.86 25.02 10.7
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表 4 梁试件屈服荷载和极限荷载降幅
Table 4. Decreasing amplitude of yield load and ultimate load of specimens
编号 ΔPy/% ΔPm/% Δμ/% B-0.3 7.4 6.0 37.0 B-0.4 10.4 7.9 28.3 B-0.5 19.6 16.9 42.9 B-0.6 33.5 23.2 57.6 B-0.7 33.7 32.4 41.8
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表 5 梁试件抗弯刚度变化和降幅
Table 5. Variation of bending rigidity of specimens and decreasing amplitude
编号 干湿循环前抗弯刚度/(kN·m2) 干湿循环后抗弯刚度/(kN·m2) 降幅/% B-0.3 32.63 31.96 2.1 B-0.4 33.82 32.14 4.9 B-0.5 27.43 25.18 8.2 B-0.6 28.88 24.36 15.7 B-0.7 30.34 20.58 32.2 B-0 41.03
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表 6 氯离子含量分布函数的参数拟合结果
Table 6. Fitting results of parameters of chloride ion content distribution function
编号 裂缝区 非裂缝区 
Cs/% D/(mm2·d-1) Cs/% D/(mm2·d-1) B-0.3 2.05 2.10 1.75 1.65 1.17 B-0.4 2.09 1.62 1.49 1.67 1.40 B-0.5 3.65 1.31 1.84 2.19 1.98 B-0.6 2.84 1.61 1.37 2.23 2.07 B-0.7 3.16 1.39 1.25 2.59 2.53
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