Cyclic stress-strain relationship of CFRP-confined recycled aggregates concrete under different loading rates
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摘要: 为研究碳纤维增强树脂复合材料(CFRP)约束再生骨料混凝土(RAC)在重复轴向压缩作用下的力学性能,对72根CFRP约束RAC圆柱进行了不同加载速率下的单调及重复轴压试验,分析了加载速率、再生骨料(RA)替代率和CFRP层数对CFRP约束RAC的破坏模式、极限状态、重复应力-应变关系的影响。试验结果表明:CFRP约束对100wt%RA替代率混凝土极限状态的增强效果最为显著,但其增强效果随着加载速率的增大而减小。相比于3 mm/min的加载速率,2层CFRP约束100wt%RA替代率混凝土在18 mm/min的加载速率下,其极限强度增强比降低了16.2%,极限应变增强比降低了22.6%。此外,重复轴压荷载作用下,卸载刚度和再加载刚度均与RA替代率和加载速率呈负相关,但加载速率的提升会削弱RA替代率的影响。最后,通过对试验数据的回归分析,建立了考虑加载速率与RA替代率耦合作用的CFRP约束RAC重复轴压应力-应变模型,模型预测曲线与本文的试验曲线和现有文献收集的试验曲线匹配良好。Abstract: This study experimentally investigated the mechanical behavior of carbon fiber reinforced polymer (CFRP) confined recycled aggregate concrete (RAC) under cyclic loading. In total, 72 CFRP-confined circular RAC specimens were tested under monotonic and cyclic axial compression, with a focus on the various loading rates and recycled aggregate (RA) replacement ratios. Test results indicate that the reinforcing effect of CFRP confinement on the ultimate condition of the concrete with 100wt%RA replacement ratio is most pronounced. However, this enhancement diminishes as the loading rate increases. In comparison to a loading rate of 3 mm/min, for two layers of CFRP-confined concrete with 100wt%RA replacement ratio, the enhancement ratio in ultimate strength is reduced by 16.2%, and the enhancement ratio in ultimate strain is reduced by 22.6% at a loading rate of 18 mm/min. Furthermore, under cyclic axial compression loading, both the unloading stiffness and reloading stiffness exhibit a negative correlation with the RA replacement ratio and loading rate. Nevertheless, the loading rate increase weakens the RA ratio's influence. Based on a regression analysis of the experimental data, a new cyclic stress-strain model for CFRP-confined recycled aggregate concrete incorporating the coupled effects of loading rate and RA replacement ratio is proposed. The proposed model exhibits excellent agreement with the experimental curves in this paper and the collected stress-strain curves from the opening literature.
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图 10 CFRP约束混凝土重复轴压下的典型应力-应变曲线
E2—The second stiffness; fun—Unloading stress; εun—Unloading strain; εp1—Plastic strain; Eun, 0—Unloading stiffness; Ere—Reloading stiffness; fr—Elastic limit stress; fre—Reloading stress; εre—Reloading strain; fret, env—Return envelope stress; εret, env—Return envelope strain; n—Curvature of transition zone
Figure 10. Typical stress-strain curve of CFRP-confined concrete under cyclic compression
表 1 碳纤维增强树脂复合材料(CFRP)约束再生骨料混凝土(RAC)试件设计参数
Table 1. Design parameters for carbon fiber reinforced polymer (CFRP)-confined recycled aggregate concrete (RAC) specimens
Specimen Loading type CFRP layer Loading rate/
(mm·min−1)RA replacement rate/wt% $ {f}_{\mathrm{c}\mathrm{o}} $/MPa $ {\varepsilon }_{\mathrm{c}\mathrm{o}} $/% M0.3R0%1CFRP Monotonic loading 1 0.3 0 46.3 0.244 M0.3R50%1CFRP 50 43.2 0.240 M0.3R100%1CFRP 100 36.6 0.230 M6R0%1CFRP 6 0 50.4 0.249 M6R50%1CFRP 50 47.3 0.245 M6R100%1CFRP 100 38.2 0.233 M18R0%1CFRP 18 0 52.1 0.252 M18R50%1CFRP 50 50.2 0.249 M18R100%1CFRP 100 41.0 0.237 M0.3R0%2CFRP 2 0.3 0 39.7 0.234 M0.3R50%2CFRP 50 38.6 0.233 M0.3R100%2CFRP 100 34.5 0.226 M6R0%2CFRP 6 0 42.9 0.239 M6R50%2CFRP 50 41.6 0.237 M6R100%2CFRP 100 40.8 0.236 M18R0%2CFRP 18 0 43.3 0.240 M18R50%2CFRP 50 42.5 0.239 M18R100%2CFRP 100 41.4 0.237 C0.3R0%1CFRP Cyclic loading 1 0.3 0 46.3 0.244 C0.3R50%1CFRP 50 43.2 0.240 C0.3R100%1CFRP 100 36.6 0.230 C6R0%1CFRP 6 0 50.4 0.249 C6R50%1CFRP 50 47.3 0.245 C6R100%1CFRP 100 38.2 0.233 C18R0%1CFRP 18 0 52.1 0.252 C18R50%1CFRP 50 50.2 0.249 C18R100%1CFRP 100 41.0 0.237 C0.3R0%2CFRP 2 0.3 0 39.7 0.234 C0.3R50%2CFRP 50 38.6 0.233 C0.3R100%2CFRP 100 34.5 0.226 C6R0%2CFRP 6 0 42.9 0.239 C6R50%2CFRP 50 41.6 0.237 C6R100%2CFRP 100 40.8 0.236 C18R0%2CFRP 18 0 43.3 0.240 C18R50%2CFRP 50 42.5 0.239 C18R100%2CFRP 100 41.4 0.237 Notes: M—Monotonic loading; C—Cyclic loading; The number after "M" or "C"—Loading rate; R—Recycled aggregate replacement rate; CFRP—Carbon fiber reinforced polymer; For example, C18R100%2CFRP—Two-layer CFRP-confined 100wt% recycled aggregate concrete columns with a cyclic loading rate of 18 mm/min; $ {f}_{\mathrm{c}\mathrm{o}} $—Compressive strength of unconfined RAC specimens; $ {\varepsilon }_{\mathrm{c}\mathrm{o}} $—Peak strain of unconfined RAC specimens; RA—Recycled aggregate. 表 2 RAC的配合比
Table 2. Mix ratio of RAC
RA replacement rate/wt% Water/
(kg·m−3)Cement/
(kg·m−3)NA/
(kg·m−3)RA/
(kg·m−3)Sand/
(kg·m−3)0 201 380 1128 0 691 50 201 380 564 564 691 100 201 380 0 1128 691 Note: NA—Natural aggregate. 表 3 CFRP的力学性能
Table 3. Mechanical properties of CFRP
Material $ {t}_{\mathrm{f}} $/mm $ {E}_{\mathrm{f}} $/GPa $ {f}_{\mathrm{f}} $/MPa $ {\varepsilon }_{\mathrm{f}} $/% CFRP 0.167 248.7 3820.5 1.54 Notes: $ {t}_{\mathrm{f}} $—Thickness of CFRP; $ {E}_{\mathrm{f}} $—Modulus of elasticity of CFRP; $ {f}_{\mathrm{f}} $—Ultimate tensile stress of CFRP; $ {\varepsilon }_{\mathrm{f}} $—Ultimate tensile strain of CFRP. 表 4 CFRP约束RAC试件试验结果
Table 4. Test results for CFRP-confined RAC specimens
Specimen $ {f}_{{{\rm{cu}}}} $/
MPa$ {{f}_{{{\rm{cu}}}}}/{{f}_{{{\rm{co}}}}} $ $ {\varepsilon }_{{{\rm{cu}}}} $/% $ {{\varepsilon }_{{{\rm{cu}}}}}/{{\varepsilon }_{{{\rm{co}}}}} $ $ {\varepsilon }_{{{\rm{h}}},{{\rm{rup}}}} $/% Specimen $ {f}_{{{\rm{cu}}}} $/
MPa$ {{f}_{{{\rm{cu}}}}}/{{f}_{{{\rm{co}}}}} $ $ {\varepsilon }_{{{\rm{cu}}}} $/% $ {{\varepsilon }_{{{\rm{cu}}}}}/{{\varepsilon }_{{{\rm{co}}}}} $ $ {\varepsilon }_{{{\rm{h}}},{{\rm{rup}}}} $/% M0.3R0%1CFRP-1 72.7 1.58 1.37 5.61 1.47 C0.3R0%1CFRP-1 66.7 1.44 1.23 5.03 1.42 M0.3R0%1CFRP-2 71.0 1.54 1.41 5.79 1.43 C0.3R0%1CFRP-2 72.6 1.57 1.51 6.18 1.50 M0.3R50%1CFRP-1 62.7 1.46 1.19 4.96 1.38 C0.3R50%1CFRP-1 72.5 1.68 1.50 6.23 1.61 M0.3R50%1CFRP-2 64.9 1.51 1.17 4.87 1.40 C0.3R50%1CFRP-2 68.2 1.58 1.32 5.50 1.28 M0.3R100%1CFRP-1 — — — — — C0.3R100%1CFRP-1 62.8 1.72 1.65 7.14 1.17 M0.3R100%1CFRP-2 62.3 1.73 1.61 7.04 1.36 C0.3R100%1CFRP-2 64.1 1.75 1.74 7.53 1.31 M6R0%1CFRP-1 71.0 1.42 1.17 4.71 1.36 C6R0%1CFRP-1 66.6 1.32 1.10 4.42 1.23 M6R0%1CFRP-2 73.6 1.47 1.22 4.89 0.99 C6R0%1CFRP-2 69.6 1.38 1.11 4.43 1.24 M6R50%1CFRP-1 69.5 1.48 1.27 5.16 1.14 C6R50%1CFRP-1 69.2 1.46 1.50 6.10 1.44 M6R50%1CFRP-2 71.9 1.53 1.31 5.34 1.12 C6R50%1CFRP-2 63.6 1.34 1.01 4.11 1.22 M6R100%1CFRP-1 53.6 1.41 1.06 4.56 1.25 C6R100%1CFRP-1 62.0 1.62 1.69 7.27 1.49 M6R100%1CFRP-2 58.1 1.53 1.32 5.69 1.27 C6R100%1CFRP-2 62.7 1.64 1.60 6.88 1.23 M18R0%1CFRP-1 63.6 1.22 1.00 3.96 1.09 C18R0%1CFRP-1 67.6 1.30 1.14 4.52 1.22 M18R0%1CFRP-2 72.6 1.40 1.13 4.49 1.47 C18R0%1CFRP-2 62.1 1.19 1.31 5.19 1.15 M18R50%1CFRP-1 70.8 1.42 1.17 4.71 0.99 C18R50%1CFRP-1 63.1 1.26 1.14 4.58 1.12 M18R50%1CFRP-2 72.1 1.44 1.19 4.78 1.42 C18R50%1CFRP-2 64.6 1.29 1.25 5.01 1.23 M18R100%1CFRP-1 64.1 1.56 1.28 5.39 1.35 C18R100%1CFRP-1 62.0 1.51 1.38 5.83 1.19 M18R100%1CFRP-2 62.9 1.54 1.28 5.39 1.28 C18R100%1CFRP-2 60.5 1.48 1.33 5.60 1.13 M0.3R0%2CFRP-1 93.7 2.40 2.51 10.74 1.41 C0.3R0%2CFRP-1 88.3 2.22 2.50 10.62 1.34 M0.3R0%2CFRP-2 80.8 2.07 2.09 8.94 1.17 C0.3R0%2CFRP-2 — — — — — M0.3R50%2CFRP-1 91.4 2.40 2.63 11.29 1.39 C0.3R50%2CFRP-1 92.0 2.38 2.26 9.68 1.12 M0.3R50%2CFRP-2 85.2 2.24 2.08 8.95 1.28 C0.3R50%2CFRP-2 94.4 2.45 2.28 9.78 1.36 M0.3R100%2CFRP-1 80.4 2.36 2.43 10.73 1.31 C0.3R100%2CFRP-1 89.6 2.60 3.09 13.60 1.40 M0.3R100%2CFRP-2 86.0 2.53 2.50 11.06 1.22 C0.3R100%2CFRP-2 87.6 2.54 3.05 13.42 1.54 M6R0%2CFRP-1 92.9 2.19 2.15 8.97 1.31 C6R0%2CFRP-1 94.8 2.21 2.15 8.96 1.35 M6R0%2CFRP-2 85.3 2.01 2.10 8.77 1.29 C6R0%2CFRP-2 92.1 2.15 2.30 9.59 1.38 M6R50%2CFRP-1 91.2 2.20 2.28 9.60 1.45 C6R50%2CFRP-1 92.6 2.23 2.50 10.50 1.13 M6R50%2CFRP-2 94.3 2.27 2.07 8.72 1.44 C6R50%2CFRP-2 92.5 2.22 1.91 8.03 1.13 M6R100%2CFRP-1 87.8 2.17 1.87 7.93 1.36 C6R100%2CFRP-1 90.1 2.21 2.63 11.11 1.25 M6R100%2CFRP-2 92.0 2.27 2.27 9.60 1.39 C6R100%2CFRP-2 90.3 2.21 2.41 10.16 1.41 M18R0%2CFRP-1 — — — — — C18R0%2CFRP-1 84.8 1.96 2.08 8.64 1.21 M18R0%2CFRP-2 91.5 2.13 2.44 10.16 1.36 C18R0%2CFRP-2 87.2 2.01 2.31 9.59 1.26 M18R50%2CFRP-1 87.4 2.08 2.09 8.74 1.13 C18R50%2CFRP-1 93.9 2.21 2.51 10.51 1.25 M18R50%2CFRP-2 95.1 2.26 2.31 9.67 1.22 C18R50%2CFRP-2 90.7 2.13 2.25 9.42 1.25 M18R100%2CFRP-1 84.2 2.05 2.00 8.43 1.23 C18R100%2CFRP-1 81.5 1.97 2.11 8.89 0.99 M18R100%2CFRP-2 — — — — — C18R100%2CFRP-2 89.8 2.17 2.49 10.47 1.22 Notes: $ {f}_{{{\rm{cu}}}} $—Ultimate strength of specimens; $ {f}_{{{\rm{cu}}}}/{f}_{{{\rm{co}}}} $—Ultimate strength enhancement ratio of the specimens; $ {\varepsilon }_{{{\rm{cu}}}} $—Ultimate strain of specimens; $ {\varepsilon }_{{{\rm{cu}}}}/{\varepsilon }_{{{\rm{co}}}} $—Ultimate strain enhancement ratio of the specimens; $ {\varepsilon }_{{{\rm{h}}},{{\rm{rup}}}} $—Hoop rupture strain of specimens; "—"—Data not measured; Two specimens with the same parameters were prepared, and they were distinguished by "-1" and "-2". 表 5 CFRP约束混凝土极限强度模型
Table 5. Ultimate strength model of CFRP-confined concrete
References Ultimate strength model $ \omega $ [27] $\dfrac{ {f}_{ { {\rm{cc} } } }^{ { {\rm{d} } } }}{ {f}_{ { {\rm{cc} } },0} }=1+0.1\left({ { {\rm{lg} } } }\left(\dfrac{\dot{\varepsilon } }{ {\varepsilon }_{0} }\right)\right){\left(\dfrac{ {f}_{30} }{ {f}_{ { {\rm{co} } } }}\right)}^{0.73}$ 0.1203 [33, 35] $\dfrac{ {f}_{ { {\rm{cc} } } }^{ { {\rm{d} } } }}{ {f}_{ { {\rm{cc} } },0} }=1+(0.06{ {\rm{ln} } }\left(\dfrac{ {f}_{ { {\rm{l} } } }}{ {f}_{ { {\rm{co} } } }}\right)+0.274){ { {\rm{lg} } } }\left(\dfrac{\dot{\varepsilon } }{ {\varepsilon }_{0} }\right)$ 0.3077 [34] $\dfrac{ {f}_{ { {\rm{cc} } } }^{ { {\rm{d} } } }}{ {f}_{ { {\rm{cc} } },0} }=1+\left(0.204+0.056{ {\rm{ln} } }\left(\dfrac{ {f}_{ {{\rm{l}}} } }{ {f}_{ { {\rm{co} } } }}\right)\right){ { {\rm{lg} } } }\left(\dfrac{\dot{\varepsilon } }{ {\varepsilon }_{0} }\right)$ 0.2083 Notes: $ {f}_{{{\rm{l}}}} $—Confinement stress of CFRP; $ {f}_{{{\rm{cc}}},0} $—Ultimate strength of CFRP-confined recycled aggregate concrete columns in quasi-static conditions; $ {f}_{{{\rm{cc}}}}^{{{\rm{d}}}} $—Ultimate strength of CFRP-confined recycled aggregate concrete columns in a non-quasistatic conditions; $ \dot{\varepsilon } $—Dynamic strain rate; $ {\varepsilon }_{0} $—Quasi-static strain rate, taking a value of 1.67×10–5 s–1; $ {f}_{30} $—Compressive strength of C30 concrete, taken as 30 MPa. 表 6 CFRP约束混凝土的极限应变模型
Table 6. Ultimate strain model of CFRP-confined concrete
References Ultimate strain model $ \omega $ [27] $\dfrac{ {\varepsilon }_{\mathrm{c}\mathrm{c} }^{\mathrm{d} } }{ {\varepsilon }_{\mathrm{c}\mathrm{c},0} }=1-0.1{\mathrm{l}\mathrm{g} }\left(\dfrac{\dot{\varepsilon } }{ {\varepsilon }_{0} }\right)$ 0.0940 [33, 35] $\dfrac{ {\varepsilon }_{\mathrm{c}\mathrm{c} }^{\mathrm{d} } }{ {\varepsilon }_{\mathrm{c}\mathrm{c},0} }=1.822+0.165{\mathrm{l}\mathrm{g} }\left(\dfrac{\dot{\varepsilon } }{ {\varepsilon }_{0} }\right)$ 1.3436 [34] $\dfrac{ {\varepsilon }_{\mathrm{c}\mathrm{c} }^{\mathrm{d} } }{ {\varepsilon }_{\mathrm{c}\mathrm{c},0} }=1+(0.2887\dfrac{ {f}_{\mathrm{l} } }{ {f}_{\mathrm{c}\mathrm{o} } }+0.0329){\mathrm{l}\mathrm{g} }\left(\dfrac{\dot{\varepsilon } }{ {\varepsilon }_{0} }\right)$ 0.3481 Notes: $ {\varepsilon }_{\mathrm{c}\mathrm{c},0} $—Ultimate strain of CFRP-confined concrete columns in quasi-static conditions; $ {\varepsilon }_{\mathrm{c}\mathrm{c}}^{\mathrm{d}} $—Ultimate strain of CFRP-confined concrete columns in a non-quasi-static conditions. -
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