Experimental on the shear behavior of pre-damaged RC beams strengthened by textile reinforced highly ductile concrete
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摘要: 为研究二次受力对纤维织物增强高延性混凝土(TRHDC)加固钢筋混凝土(RC)梁受剪性能的影响,对8根TRHDC加固梁和1根对比梁进行了静载试验,分析了纤维织物层数、损伤程度及持载水平对梁破坏形态、荷载-挠度曲线、荷载-箍筋应变曲线及荷载-织物应变曲线的影响。试验结果表明:所有梁均发生了剪压破坏,仅一根梁出现剥离现象;TRHDC可有效限制斜裂缝的发展,延缓箍筋屈服和刚度退化;TRHDC加固显著地提高了梁的受剪承载力和变形能力,最高分别达67%和54%;加固效果未完全随纤维织物层数的增大而提高,与TRHDC面层利用率有关;原梁箍筋屈服之前,损伤程度对加固梁受剪性能的影响不明显,原梁箍筋屈服之后,加固梁受剪承载力随损伤程度的增大而降低;加固效果随持载水平的提高而降低;两层纤维织物的TRHDC可有效修复完全受损RC梁的受剪性能;建立了考虑二次受力的TRHDC加固RC梁受剪承载力的计算公式,且计算值与试验结果吻合较好。
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关键词:
- 纤维织物增强高延性混凝土 /
- 受损RC梁 /
- 受剪加固 /
- 二次受力 /
- 受剪承载力
Abstract: Static load tests were conducted on eight reinforced concrete (RC) beams strengthened by textile reinforced high ductile concrete (TRHDC) and one control beam to study the effect of secondary loading on the shear behavior of TRHDC-strengthened beams. The influence of the number of the textile layer, damage degree of beams, and different sustained loads on the failure mode, load-deflection curves, load-strain curves of stirrups, and load-strain curves of textile were analyzed. The results indicate that all beams fail in shear compression mode, and the debonding phenomenon is only observed in one beam. TRHDC can effectively restrain the development of shear cracks, delay the yielding of stirrups and the stiffness degradation. This strengthening method can significantly improve the shear strength and deformation capacity of RC beams by up to 67% and 54%, respectively. The strengthening effectiveness does not completely increase with the number of the textile layer increase, which is related to the utilization rate of the TRHDC layer. When the stirrup of the original beam does not reach its yielding strength, the damage degree has no obvious influence on the shear behavior of strengthened beams. On the contrary, the shear strength of strengthened beams decreases with the increase of the damage degree. The strengthening effectiveness decreases with the sustained load increasing. The completely damaged RC beams can be restored by the TRHDC with two numbers of the textile layer. A calculation formula for the shear strength of TRHDC-strengthened beams considering the secondary loading was proposed. The calculation values are in good agreement with the test results. -
图 11 RC梁拉-压杆模型
Figure 11. Strut-and-tie model of RC beams
$ {f_1} $ and $ {f_2} $—Principal tensile and compressive stresses at the node B zone, respectively; $ {\theta _{\text{s}}} $—Angle between the longitudinal tension reinforcement and the diagonal strut; h—Depth of RC beams; $ {d_{\text{c}}} $—Distance from the centroid of the nodal A zone to the centroid of the nodal B zone; $ {l_{\text{d}}} $ and $ {l_{\text{c}}} $—Depths of the nodal A and B zones, respectively; a—Distance from loading point to support; $ {l_{\text{b}}} $—Width of the nodal B zone; $ {V_{{\text{RC}}}} $—Shear strength of RC beams; $ {C_{\text{C}}} $—Compressive force of the concrete in the shear compression zone; $ {T_{\text{s}}} $—Tensile force of longitudinal reinforcements; $ {F_{\text{c}}} $—Compressive force of the concrete diagonal struts
表 1 钢筋混凝土(RC)梁试件加固参数
Table 1. Strengthening parameters of reinforced concrete (RC) beam specimens
Specimen Damage
degreeUnloading
levelNumber of the
textile layer in
TRHDCL-0 – – – CL-1 – – 1 CL-2 – – 2 CL-3 – – 3 SCL-1 Shear cracks occurred
(47%Pu,0)Unloading completely 2 SCL-2 Stirrups yielded (56%Pu,0) Unloading completely 2 SCL-3 Failure (the load drops to 85%Pu,0) Unloading completely 2 XCL-1 Shear cracks occurred
(47%Pu,0)Unloading 23.5%Pu,0 2 XCL-2 Shear cracks occurred
(47%Pu,0)Not unloading 2 Notes: Pu,0—Peak load of the control beam; L—Control beam; CL—Strengthened beams without initial stress; SCL—Strengthened beams with different damage degrees; XCL—Strengthened beams under sustained loads; TRHDC—Fiber reinforced high ductility concrete. 表 2 钢筋力学性能
Table 2. Mechanical properties of reinforcement
Type Diameter/mm Yielding strength/MPa Ultimate strength/MPa HPB300 6 343 508 HRB400 18 438 610 HRB400 25 450 620 表 3 织物力学性能
Table 3. Mechanical properties of textile
Type of textile ft/MPa Ef/GPa $ {\varepsilon _{\text{t}}} $/% $ {\rho _{\text{f}}} $/(g·cm−3) A/(mm2·bundle−1) Carbon 3600 230 1.5 1.74 0.88 Notes: ft—Tensile strength; Ef—Elastic modulus; $ {\varepsilon _{\text{t}}} $—Tensile elongation; $ {\rho _{\text{f}}} $—Density; A—Cross-sectional area of each bundle of yarns. 表 4 高延性混凝土(HDC)的基体配合比
Table 4. Mixed proportions of matrices in high ductile concrete (HDC)
(kg/m3) Cement Flyash Mineral powder River sand Water Water reducer 235 764 177 424 376 8 表 5 聚乙烯醇(PVA)纤维的力学性能指标
Table 5. Mechanical properties of polyvinyl alcohol (PVA) fibers
Fiber type L/mm D/μm E/GPa f/MPa $ \varepsilon $/% $ \rho $/(g·cm−3) PVA 12 39 40 1600 7 1.3 Notes: L—Length; D—Diameter; E—Elastic modulus; f—Tensile strength; $ \varepsilon $—Tensile elongation; $ \rho $—Density. 表 6 各RC梁试验结果
Table 6. Test results of RC beams
Specimen
number$ {P_{{\text{cr}}}} $/kN $\dfrac{ { {P_{ {\text{cr} } } } } }{ { {P_{ {\text{cr,0} } } } } }$ $ {P_{\text{r}}} $/kN $\dfrac{ { {P_{\text{r} } } }}{ { {P_{ {\text{r,0} } } } } }$ $ {P_{\text{u}}} $/kN $\dfrac{ { {P_{\text{u} } } }}{ { {P_{ {\text{u,0} } } } } }$ $ {\varDelta _{\text{u}}} $/mm $\dfrac{ { {\varDelta _{\text{u} } } }}{ { {\varDelta _{ {\text{u,0} } } } } }$ Failure
modeL-0 42 — 172 — 367.56 — 5.88 — S CL-1 250 5.95 335 1.95 585.54 1.59 9.05 1.54 S CL-2 190 4.52 330 1.92 563.90 1.53 6.96 1.18 S CL-3 300 7.14 410 2.38 615.49 1.67 7.97 1.36 S+PD SCL-1 180 4.29 300 1.74 528.38 1.44 6.71(0.63) 1.14 S SCL-2 165 3.93 280 1.63 565.22 1.54 6.60(0.61) 1.12 S SCL-3 160 3.81 223 1.30 434.91 1.18 6.71(2.59) 1.14 S XCL-1 210 5.00 320 1.86 498.76 1.36 5.62(1.29) 0.96 S XCL-2 200 4.76 280 1.63 485.03 1.32 5.24(1.86) 0.89 S Notes: $ {P_{{\text{cr}}}} $ and $ {P_{{\text{cr,0}}}} $—Cracking load of the strengthened beam and control beam, respectively; $ {P_{\text{r}}} $ and $ {P_{{\text{r,0}}}} $—Loads corresponding to the yielding of stirrups of the strengthened beam and control beam, respectively; $ {P_{\text{u}}} $ and $ {P_{{\text{u,0}}}} $—Peak load of the strengthened beam and control beam, respectively; $ {\varDelta _{\text{u}}} $ and $ {\varDelta _{{\text{u,0}}}} $—Ultimate deflection corresponding to the load dropping to 85% of the peak load of the strengthened beam and control beam, respectively; $ {\varDelta _{\text{u}}} $ of specimens SCL-1, SCL-2, SCL-3, XCL-1, and XCL-2 is the midspan deflection under secondary loading, while the values in parentheses are the residual midspan deflection before secondary loading; S—Shear-compression failure; PD—Debonding failure between the concrete and the TRHDC layer. 表 7 各RC梁受剪承载力计算值与试验值比较
Table 7. Comparison for the calculation values and test results of shear strength of RC beams
Resource Strengthening method Specimen number $ {P_{{\text{u,t}}}} $/kN $ {P_{{\text{u,cal}}}} $/kN ${ { {P_{ {\text{u,cal} } } } } }/{ { {P_{ {\text{u,t} } } } } }$ This study — L-0 183.78 218.02 1.19 Non-damaged strengthened beams CL-1 292.77 259.43 0.89 CL-2 281.95 281.50 1.00 CL-3 307.74 301.64 0.98 Pre-damaged strengthened beams SCL-1 264.19 281.50 1.06 SCL-2 282.61 281.50 1.00 SCL-3 217.45 217.40 1.00 Pre-damaged strengthened beams under sustained load XCL-1 249.38 242.53 0.97 XCL-2 242.52 242.53 1.00 Literature [31] Pre-damaged strengthened beams J3 B 212 200.89 0.95 J3 C 200 189.78 0.95 J3 D 178 178.86 1.00 Pre-damaged strengthened beams under sustained load J6 C 166 175.64 1.06 J6 D 160 171.20 1.07 Literature [32] Pre-damaged strengthened beams under sustained load L1Rd2P2A212-70 342.00 288.200 0.84 L1Rd2P2A211-70 410.50 332.950 0.81 L2Rd2P2A212-70 344.50 275.033 0.80 L2Rd2P2A211-70 440.50 323.608 0.74 Notes: $ {P_{{\text{u,t}}}} $—Experimental value of the specimen; $ {P_{{\text{u,cal}}}} $—Calculated value of the specimen. -
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