A MODEL OF CALCULATING THE BOND STRENGTH BETWEEN REBARS AND CONCRETE CONSIDERING THE SOFTENING EFFECT OF CONCRETE
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摘要: 通过钢筋与混凝土拉式粘结试验,测试了高强度带肋钢筋与不同强度等级混凝土的粘结强度,分析了带肋钢筋与混凝土的粘结受力机理;采用双线性软化本构对开裂区的软化行为进行描述,建立了综合考虑开裂区及未开裂区混凝土影响的粘结强度理论计算模型;研究了开裂区不同径向位移分布对计算结果的影响,并将计算结果与试验结果进行对比,验证了计算模型的有效性。结果表明:模型采用基于等效弹性假设的开裂区径向位移分布时,计算值与试验值最为吻合,但却过高的估计了低强度混凝土试件的粘结强度;为确保有足够的安全储备,建议采用弹性假设作为开裂区混凝土径向位移分布。Abstract: The bond strength between high-strength rebars and concrete with different strengths was tested by pull-out tests. The bonding mechanism between rebars and concrete was analyzed. The bilinear softening constitutive model was used to describe the softening behavior of concrete in the cracked zone, and the theoretical calculation model of the bond strength considering the influence of concrete in cracked and non-cracking zones were established. The effects of different radial displacement distributions in the cracked zone on the calculation results are studied. The validity of the calculation model was verified by comparing the calculated results with the experimental results. The results show that the computational model has the best accuracy when the radial displacement distribution in the fracture zone is assumed to be equivalently elastic. However, the bond strength of low-strength concrete specimens was overestimated under this assumption. It is suggested that the elastic assumption be used as the radial displacement distribution of concrete in the cracked zone to ensure adequate safety reserves.
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Key words:
- reinforced concrete /
- bonding /
- failure mechanisms /
- bond strength /
- analytical models /
- computational methods
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表 1 拉式粘结试验结果
Table 1. Bond test results
试件编号 钢筋直径/mm 锚固长度/mm 保护层厚度/mm 混凝土抗压强度/MPa 混凝土抗拉强度/MPa 粘结强度均值/MPa 粘结强度标准差/MPa T16-7d-C30 16 115 92 40.69 3.03 18.65 3.41 T16-7d-C40 16 115 92 50.32 3.41 24.94 1.83 T16-7d-C50 16 115 92 56.02 3.62 25.79 1.52 表 2 粘结强度的理论计算值
Table 2. Calculation value of bond strength
试件编号 参数C1/mm 按假设①计算 按假设②计算 按假设③计算 ru1/mm ${\tau} _{ {\text{u1} } }^{\text{c} }$/MPa ru2/mm ${\tau} _{ {\text{u2} } }^{\text{c} }$/MPa ru3/mm ${\tau} _{ {\text{u3} } }^{\text{c} }$/MPa T16-7d-C30 −174.97 69.85 24.55 52.96 18.54 57.33 21.10 T16-7d-C40 168.11 69.04 27.34 51.97 20.49 56.58 23.44 T16-7d-C50 −164.15 68.55 28.84 51.38 21.52 56.13 24.69 A18-10d-C40[2] −209.56 73.93 10.48 57.95 8.71 61.11 9.30 A18-10d-C50[2] −207.28 73.66 11.41 57.62 9.36 60.86 10.08 A18-10d-C60[2] −204.05 73.28 12.72 57.16 10.27 60.51 11.18 B18-20d-C60[21] −208.86 73.85 10.77 57.85 8.91 61.04 9.54 B18-20d-C80[21] −204.73 73.59 11.66 57.53 9.53 60.79 10.29 B18-20d-C100[21] −201.50 72.98 13.76 56.79 11.00 60.23 12.05 注:1) 为便于对比分析,所收集数据试件编号按照本文试件编号规则重新赋予编号,例如A18-10d-C40含义为钢筋公称直径为18 mm、锚固长度为10 d、混凝土强度等级为C40的试件;2) 每组收集数据为3个试件实测值的平均值;3) 相同强度等级混凝土实测强度值存在差异,所收集数据中详细试验参数见相应文献;4) ru1、ru2、ru3分别为假设①、②、③下计算得到的裂缝深度;5) ${\tau} _{ {\text{u1} } }^{\text{c} } $、${\tau} _{ {\text{u2} } }^{\text{c} } $、${\tau} _{ {\text{u3} } }^{\text{c} } $分别为假设①、②、③下计算得到的粘结强度。 表 3 粘结强度理论计算值与试验值的对比
Table 3. Comparisons between calculated and experimental values of bond strength
试件编号 试验值${\tau} _{\text{u} }^{\text{t} }$/MPa ${ {{\tau} _{ {\text{u1} } }^{\text{c} } } \mathord{/ {\vphantom { {{\tau} _{ {\text{u1} } }^{\text{c} } } {{\tau} _{\text{u} }^{\text{t} } } }} } {{\tau} _{\text{u} }^{\text{t} } } }$ ${ {{\tau} _{ {\text{u2} } }^{\text{c} } } \mathord{/ {\vphantom { {{\tau} _{ {\text{u2} } }^{\text{c} } } {{\tau} _{\text{u} }^{\text{t} } } }} } {{\tau} _{\text{u} }^{\text{t} } } }$ ${ {{\tau} _{ {\text{u3} } }^{\text{c} } } \mathord{/ {\vphantom { {{\tau} _{ {\text{u3} } }^{\text{c} } } {{\tau} _{\text{u} }^{\text{t} } } }} } {{\tau} _{\text{u} }^{\text{t} } } }$ T16-7d-C30 18.65 1.33 1.00 1.15 T16-7d-C40 24.94 1.10 0.82 0.95 T16-7d-C50 25.79 1.16 0.87 0.99 A18-10d-C40 8.92 1.17 0.98 1.04 A18-10d-C50 10.45 1.09 0.90 0.96 A18-10d-C60 11.56 1.10 0.89 0.97 B18-20d-C60 10.31 1.04 0.86 0.93 B18-20d-C80 11.50 1.01 0.83 0.89 B18-20d-C100 12.45 1.11 0.88 0.97 注:${ { {\tau} _{ {\text{u1} } }^{\text{c} } } \mathord{/ {\vphantom { { {\tau} _{ {\text{u1} } }^{\text{c} } } { {\tau} _{\text{u} }^{\text{t} } } } } } { {\tau} _{\text{u} }^{\text{t} } } } $、${ {{\tau} _{ {\text{u2} } }^{\text{c} } } \mathord{/ {\vphantom { {{\tau} _{ {\text{u2} } }^{\text{c} } } {{\tau} _{\text{u} }^{\text{t} } } }} } {{\tau} _{\text{u} }^{\text{t} } } } $、${ {{\tau} _{ {\text{u3} } }^{\text{c} } } \mathord{/ {\vphantom { {{\tau} _{ {\text{u3} } }^{\text{c} } } {{\tau} _{\text{u} }^{\text{t} } } }} } {{\tau} _{\text{u} }^{\text{t} } } } $分别为假设①、②、③下计算得到的粘结强度与试验实测粘结强度的比值。 -
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