Study on calculation method of RC beam's shear bearing capacity of CFRP grid-polymer cement mortar
-
摘要: 为揭示碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)网格-聚合物水泥砂浆(Polymer cement mortar,PCM)抗剪加固钢筋混凝土(RC)梁的受剪机制并建立其承载力计算方法,对RC梁进行了四点弯曲试验和有限元模拟,重点分析了CFRP网格对RC加固梁的抗剪贡献,建立了基于改进的桁架拱模型的抗剪承载力计算方法。结果表明:RC梁侧粘贴CFRP网格-PCM加固层不仅可以抑制斜裂缝的发展,而且还提高了抗剪承载力;CFRP网格与钢筋之间具有良好的协同工作性能,其中,横向CFRP网格筋分担了约16%的箍筋应变;回归分析指出纵向CFRP网格筋的应变约为横向CFRP网格筋应变的0.29倍;综合考虑纵向CFRP网格的销栓作用和横向CFRP网格分担的箍筋应变,提出了基于改进桁架-拱模型的承载力计算方法,具有更好的适用性和准确性,能够满足设计要求。
-
关键词:
- CFRP网格-PCM抗剪加固RC梁 /
- 四点弯曲试验 /
- 有限元分析 /
- 改进的桁架-拱模型 /
- 承载力计算方法
Abstract: In order to reveal the shear mechanism of the carbon fiber reinforced polymer (CFRP) grid-polymer cement mortar (PCM) shear reinforced reinforced concrete (RC) beam and establish its bearing capacity calculation method, four-point bending tests and finite element simulation were conducted on the RC beams. The shear contribution of the CFRP grid to the RC reinforced RC beam was analyzed, and the shear bearing capacity calculation method was established based on the improved truss arch model. The results show that the CFRP grid-PCM reinforcement layer can not only inhibit the development of inclined cracks, but also improve the shear bearing capacity. CFRP grid and reinforcement have good cooperative working performance, where the horizontal CFRP grid shares about 16% of the stirrup strain. Regression analysis indicates that the strain of the vertical CFRP grid is about 0.29 times than that of the horizontal CFRP grid. Comprehensively considering the dowel action of the longitudinal CFRP grid and the stirrup strain shared by the horizontal CFRP grid, the bearing capacity calculation method is presented based on the improved truss-arch model, which has better applicability and accuracy to meet the design requirements. -
表 1 试件设计
Table 1. Specimen design
Specimen Existing steel bars FRP grid Shear
span λPCM thickness/
mmExisting vertical reinforcement ratio/% Anti-shear reinforcement ratio/% Tensile reinforcement Handling reinforcement Stirrup BS D32-SD345 D10-SD345 D10-SD345@200 — 2.63 — 5.8 0.36 BG D32-SD345 — — CR8-100×100 20 5.6 0.22 BGS D32-SD345 D10-SD345 D6-SD345@200 CR8-100×100 20 5.8 0.35 Notes: B—Reinforced concrete beam; S—Beam is equipped with stirrup; G—Stick carbon fiber reinforced polymer (CFRP) grid-polymer cement mortar (PCM) reinforcement layer on both sides; BS—Reinforced concrete beams provided with stirrups; BG—Reinforced concrete beam with only CFRP-PCM reinforced layer without stirrup; BGS—Reinforced concrete beams with stirrups and CFRP-PCM reinforcement layer; D—Diameter; SD—Reinforcement strength grade; CR8—CFRP grid of 8 mm in diameter; FRP—Fiber reinforced polymer. 表 2 混凝土配合比
Table 2. Concrete mix proportion
Maximum
grain size/mmColony/
mmWater cement
ratio/%Air ratio/% Measurement unit/(kg·m–3) Water Cement Fine aggregate Coarse aggregate Admixture 20 120 55.6 4.5 158 284 792 1126 1.3 表 3 混凝土和聚合物水泥砂浆(PCM)材料性能
Table 3. Properties of concrete and polymer cement mortar (PCM) materials
Material Compression strength/MPa Tensile strength/MPa Modulus of elasticity/GPa Concrete 34.1 2.92 31.9 PCM 36.7 2.87 30.1 表 4 钢筋与碳纤维增强树脂复合材料(CFRP)网格的力学性能
Table 4. Mechanical properties of steel and carbon fiber reinforced polymer (CFRP) grids
Material Type Cross-sectional area/mm2 Yield strength
/MPaModulus of elasticity/GPa Tensile strength
/MPaConcrete iron D32 794.2 389 200 587 D10 71.3 413 200 561 D6 31.7 417 200 570 CFRP grid CR8 26.4 — 100 1400 表 5 混凝土塑性损伤模型参数取值
Table 5. Parameters of plastic damage model for concrete
Type Expansion angle ψ Offset ε $ {\sigma _{{\text{b0}}}}/{\sigma _{{\text{c0}}}} $ Kc Coefficient of viscosity μ Value 38 0.1 1.16 0.6667 0.0005 Notes: $ {\sigma _{{\text{b0}}}}/{\sigma _{{\text{c0}}}} $—Ratio of biaxial and uniaxial compression limit strength; Kc—Ratio of stretching and the second stress invariant on the compression meridian. 表 6 CFRP网格-PCM加固RC梁试验结果汇总
Table 6. Summary of test results for CFRP grid-PCM shear-reinforced RC beams
Specimen Peak load P/kN
$ {P_{\text{t}}}/{P_{\text{c}}} $Cross-mid deflection D/mm
$ {D_{\text{t}}}/{D_{\text{c}}} $Shear cracking load Ps/kN
$ {P_{{\text{st}}}}/{P_{{\text{sc}}}} $Test value
Pt/kNSimulation value
Pc/kNTest value
Dt/mmSimulation value
Dc/mmTest value
Pst/kNSimulation value
Psc/kNBS 690 614 1.12 8.35 8.07 1.03 210 172 1.22 BG 617 601 1.03 7.09 6.77 1.05 225 188 1.19 BGS 757 722 1.05 7.40 7.39 1.00 320 256 1.25 表 7 RGS试件参数信息
Table 7. Parameter information of RGS specimens
Specimen Stirrup Stirrup ratio
/%Grid type-spacing: Vertical and horizontal
/(mm×mm)Reinforcement ratio
/%Ultimate load
/kNRGS-S200 D6-SD345@200 0.16 CR8-100×100 0.22 722.2 RGS-S150 D6-SD345@150 0.21 737.7 RGS-S100 D6-SD345@100 0.32 746.4 RGS-H100 V150 D6-SD345@200 0.16 CR8-100×150 0.15 711.9 RGS-H100 V100 CR8-100×100 0.22 722.2 RGS-H100 V50 CR8-100×50 0.44 774.2 Notes: RGS—Reinforced concrete (RC) beam with stirrup and CFRP-PCM reinforcement layer; S200—Stirrup spacing is 200 mm; H—Horizontal grid spacing; V—Vertical grid spacing. 表 8 CFRP网格-PCM加固RC梁试件与未加固试件参数信息
Table 8. Parameter information of CFRP grid-PCM shear-reinforced RC beam specimens and unreinforced specimens
Type of specimen Specimen number Vertical reinforcement Stirrup CFRP grid PCM thickness
/mmHorizontal grid ratio/% Tensile reinforcement Compressive reinforcement First group NRS-50 6-D32-SD345 2-D10-SD345 D6-SD345@200 — — — RGS-50 CR8@50 20 0.44 Second group NRS-100 — — — RGS-100 CR8@100 20 0.22 Third group NRS-150 — — — RGS-150 CR8@150 20 0.15 Notes: NRS-50—Reinforced concrete (RC) beam with no CFRP-PCM reinforcement layer but with stirrup in 50 mm spacing (NRS-100 and NRS-150 are in the same manner); RGS-50—Reinforced concrete (RC) beam with CFRP-PCM reinforcement layer and stirrup in 50 mm spacing (RGS-100 and RGS-150 are in the same manner). 表 9 纵向和横向CFRP网格应变信息汇总
Table 9. Summary of grid strain information for horizontal and vertical CFRP
Specimen Shear
span λConcrete strength/MPa CFRP grid
typeRatio $ {\rho _{\text{g}}} $/% PCM thickness/ mm Vertical grid strain
$ {\varepsilon _{{\text{ver}}}} $/$ {10^{ - 6}} $Horizontal grid strain
$ {\varepsilon _{{\text{hor}}}} $/$ {10^{ - 6}} $Tensile
strength $ {f_{\text{t}}} $Compression strength
$ {f_{\text{c}}} $RGS1 2.6 2.92 34.1 CR8@50 0.44 20 2853.17 367.52 2993.50 511.91 2919.94 548.94 RGS2 2.6 2.92 34.1 CR8@100 0.22 2581.23 551.82 2837.57 1003.05 2599.29 920.19 RGS3 2.6 2.92 34.1 CR8@150 0.15 2029.87 825.87 3905.37 1088.63 3461.74 988.99 RGS4 1.8 2.92 34.1 CR8@100 0.22 3735.11 913.96 3564.48 1299.26 3570.80 1245.58 RGS5 2.2 2.92 34.1 CR8@100 0.22 3625.54 1150.78 3141.04 1094.90 3260.70 1078.79 RGS6 2.6 2.20 26.6 CR8@100 0.22 2337.90 571.62 2200.77 770.38 2289.55 794.90 RGS7 2.6 2.64 38.0 CR8@100 0.22 2494.30 704.24 3012.34 1069.08 2389.03 834.12 表 10 不同FRP网格抗剪加固RC梁抗剪承载力计算值与试验值比较
Table 10. Comparison of calculated and experimental values of shear capacity of RCbeams strengthened with different FRP grids
Data
sourcesSpecimen $ {P_{{\text{exp}}}} /{\rm{kN}}$ $ {P_{{\text{cal}}}} $[5]/kN $ {P_{{\text{cal}}}}/{\rm{kN}} $ $ {P_{{\text{exp}}}}/{P_{{\text{cal}}}} $[5] $ {P_{{\text{exp}}}}/{P_{{\text{cal}}}} $ $ {P_{{\text{exp}}}}/{P_{{\text{cal}}}} $ analysis $ {P_{{\text{exp}}}}/{P_{{\text{cal}}}} $[5] analysis Mean
valueVariable
coefficientMean
valueVariable
coefficientText BG 617 330 466 1.87 1.32 1.22 0.16 1.85 0.32 BGS 757 414 562 1.83 1.35
[5]RCF4 881 768 625 1.15 1.41 RCF6 949 887 704 1.07 1.35 RCF8 943 939 769 1.00 1.23 RCF4’ 950 810 721 1.17 1.32 RCF64 860 823 704 1.04 1.22
[6]PGB 352 105 290 3.35 1.21
[11]S150-CGM 677 449 458 1.51 1.48 S250-CGM 571 248 428 2.30 1.33
[12]L3 373 186 385 2.00 0.97 L4 511 253 385 2.01 1.33
[21]NO.2 588 320 408 1.84 1.44 NO.4 631 332 498 1.90 1.27
[22]SB1 376 245 304 1.53 1.24 SB2 449 230 446 1.95 1.01 SB3 471 190 601 2.48 0.78
[23]SB2-3 449 229 441 1.96 1.02
[24]D 195 122 255 1.60 0.76
[25]C35 S3-M2-G2 674 261 472 2.58 1.43 C40 S0-M2-G2 bc 484 181 395 2.67 1.22 Notes: $ {P_{{\text{cal}}}} $—Shear bearing capacity of the FRP grid reinforced RC beam which is calculated based on the proposed method; $ {P_{{\text{exp}}}} $—Shear bearing capacity of the FRP grid reinforced RC beam which is calculated based on the corresponding test; RCF4, RCF6 and RCF8—Reinforced by CR4 CFRP, CR6 CFRP and CR8 CFRP grid whose vertical reinforcement interval was 50 mm compared with 150 mm of other specimens (CR4, CR6 and CR8 are the type of the CFRP grid in ABAQUS); RCF4'—Reinforced by CR4 CFRP grid whose vertical reinforcement interval was 50 mm compared with 50 mm of other specimens; RCF64—Reinforced by CR6&4 CFRP grid whose horizontal grid was CR4 and vertical grid was CR6; PGB—Beam was strengthened with high strength PCM and high strength carbon fiber-reinforced plastics (CFRP) gride bars; S150-CGM and S250-CGM—Beam with CFRP grid embedded in mortar (CGM), and the beam with 6 mm stirrups @150 mm c/c and @250 mm c/c; L3—Fiber grid and polymer mortar reinforced concrete beams (FRP GRID&NC-RC); L4—Fiber grid and engineered cementitous composite (ECC) reinforced concrete beams (FRP GRID&ECC-RC); NO.2 and NO.4—Beam with 2 row and 4 row of CFRP grid; SB1, SB2, SB3—FRP grid used in the ultra high toughness cementitious composite (UHTCC) layer (Measured thickness: 1 mm, 3 mm and 5 mm respectively); SB2-3—A 3 mm BFRP grid reinforced ECC composite SB2 reinforced concrete beam; D—RC beam strengthened with FRP grid; C35 S3-M2-G2—Beam C35 S3 with stirrup was strengthed by the use of mortar 2 and grid M; C40 S0-M2-G2 bc—Beam C40 S0 without stirrup but was strengthed by the use of mortar 2 and grid M; c/c—Center/Center; BFRP—Boron fiber reinforced plastic. -
[1] 袁廷朋, 陆洲导, 张鑫. 钢筋混凝土结构受氯离子严重腐蚀后的加固处理[J]. 四川建筑科学研究, 2007, 33(1):98-99. doi: 10.3969/j.issn.1008-1933.2007.01.028YUAN Tingpeng, LU Zhoudao, ZHANG Xin. Reinforcement of reinforced concrete structure after severe corrosion by chloride ion[J]. Architectural Science Research in Sichuan,2007,33(1):98-99(in Chinese). doi: 10.3969/j.issn.1008-1933.2007.01.028 [2] WANG B U, JI K, WU T, et al. Experimental investigation of stress transfer and failure mechanism between existing concrete and CFRP grid-sprayed PCM[J]. Construction and Building Materials,2019,215:43-58. doi: 10.1016/j.conbuildmat.2019.04.168 [3] WANG B, WANG Z, UJI K. Experimental verification of a novel anchorage method of CFRP grid in mortar[J]. Structures,2020,28:1646-1660. doi: 10.1016/j.istruc.2020.09.044 [4] 江佳斐, 隋凯. 纤维网格增强超高韧性水泥复合材料加固混凝土圆柱受压性能试验[J]. 复合材料学报, 2019, 36(8):1957-1967.JIANG Jiafei, SUI Kai. Experimental study of compression performance of concrete cylinder strengthened by textile reinforced engineering cement composites[J]. Acta Materiae Compositae Sinica,2019,36(8):1957-1967(in Chinese). [5] GUO R, PAN Y, CAI L H, et al. Study on design formula of shear capacity of RC beams reinforced by CFRP grid with PCM shotcrete method[J]. Engineering Structures,2018,166:427-440. doi: 10.1016/j.engstruct.2018.03.095 [6] AMIRUDDIN A A. Shear behavior of concrete beams strengthened with CFRP grid and PCM shotcrete[J]. EPI International Journal of Engineering,2019,2(1):5-8. doi: 10.25042/epi-ije.022019.02 [7] KHALIFA A. Rehabilitation of rectangular simply supported RC beams with shear deficiencies using CFRP composites[J]. Construction and Building Materials,2002,16(2):135-146. [8] 曹亮, 张海燕, 吴波. 纤维编织网增强低聚物砂浆加固钢筋混凝土梁受剪性能研究[J]. 工程力学, 2019, 36(1):207-215. doi: 10.6052/j.issn.1000-4750.2017.11.0881CAO Liang, ZHANG Haiyan, WU Bo. Shear performance research on reinforced concrete beams strengthened with the fiber woven mesh and oligomic mortar[J]. Engineering Mechanics,2019,36(1):207-215(in Chinese). doi: 10.6052/j.issn.1000-4750.2017.11.0881 [9] 中国工程建设标准化协会. 碳纤维片材加固混凝土结构技术规程: CECS 146—2003[S]. 北京: 中国计划出版社, 2007.China Engineering Construction Standardization Association. Standardization of engineering construction: CECS 146—2003[S]. Beijing: China Planning Press, 2007(in Chinese). [10] 郑宇宙. FRP格栅增强ECC复合加固混凝土梁试验与计算方法研究[D]. 南京: 东南大学, 2018.ZHENG Yuzhou. Experiment and calculation method research on reinforced concrete (RC) beams strengthened with the composite of FRP grid and ECC[D]. Nanjing: Southeast China University, 2018(in Chinese). [11] AZAM R, SOUDKI K, WEST J S, et al. Strengthening of shear-critical RC beams: Alternatives to externally bonded CFRP sheets[J]. Construction and Building Materials,2017,151:494-503. doi: 10.1016/j.conbuildmat.2017.06.106 [12] 陈文永, 陈小兵, 丁一, 等. 纤维网格及ECC材料抗剪加固性能研究[J]. 工业建筑, 2009, 39(12):118-122.CHEN Wenyong, CHEN Xiaobing, DING Yi, et al. The shear behavior of concrete beam reinforced with ECC and FRP grid[J]. Industrial Architecture,2009,39(12):118-122(in Chinese). [13] GUO R, CAI L H, HINO S, et al. Experimental study on shear strengthening of RC beams with FRP grid-PCM reinforcement layer[J]. Applied Sciences,2019,9(15):1-21. doi: 10.3390/app9152984 [14] Concrete Committee of Civil Engineering Society. Civil engineering society concrete standard square document[S]. Japan: Japan Civil Engineering Society, 2007(in Chinese). [15] NAKAMURA S, YAMAGUCHI K, ARWINM A. Bending reinforcing effect of RC beams using a two-layer contact placed CFRP grid by PCM spraying method[J]. Proceeding of the Japan Concrete Institute,2009,131(2):1429-1434. [16] MIYANO N, YAMAGUCHI K, TANIGUCHI K. Shear capacity for RC beam retrofitted by CFRP covering PCM shotcrete[J]. Proceedings of the Japan Concrete Institute,2013,35(2):1423-1428. [17] 刘巍, 徐明, 陈忠范. ABAQUS混凝土损伤塑性模型参数标定及验证[J]. 工业建筑, 2014, 44(S1):167-171, 213.LIU Wei, XU Ming, CHEN Zhongfan. Parameters calibration and verification of concrete damage plasticity model of ABAQUS[J]. Industrial Architecture,2014,44(S1):167-171, 213(in Chinese). [18] Japan Road Association. Specifications for highway bridges, Part V seismic design[S]. Tokyo: Japan Road Association, 2002. [19] 国家标准抗震规范管理组. 建筑抗震设计规范: GB/T 50011—2010[S]. 北京: 中国建筑工业出版社, 2016.National Standard Seismic Code Management Group. Code for the seismic design of buildings: GB/T 50011—2010[S]. Beijing: China State Construction Industry Press, 2016(in Chinese). [20] American Concrete Institute. Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures: ACI 440.2 R-08[S]. Farmington Hills: American Concrete Institute, 2008. [21] LIANG J, UJI K, MATSUMURA S, et al. Shear strengthening of RC beam with CFRP grid and sprayed mortar[J]. Proceeding of the Japan Concrete Institute,2008,30(2):607-612. [22] 郑宇宙, 王文炜, 戴建国, 等. FRP-UHTCC复合层抗剪增强钢筋混凝土梁受力性能试验研究[J]. 建筑结构学报, 2019(8): 118-126.ZHENG Yuzhou, WANG Wenwei, DAI Jianguo, et al. Experimental study on mechanical performance of reinforced concrete beams shear-strengthened with FRP-UHTCC composite[J]. Journal of Architectural Structures, 2019(8): 118-126(in Chinese). [23] 王文炜, 郑宇宙. BFRP格栅增强ECC加固钢筋混凝土梁抗剪承载力试验研究[C]//第九届全国建设工程FRP应用学术交流会. 重庆: 中国土木工程学会FRP及工程应用专业委员会, 2015: 326-331.WANG Wenwei, ZHENG Yuzhou. Experimental research on shear capacity of concrete beams strengthened with BFRP grid reinforced ECC[C]//The 9th National Construction Engineering FRP Application Academic Exchange Conference. Chongqing: FRP and Engineering Application Professional Committee of the Chinese Society of Civil Engineering, 2015: 326-331(in Chinese). [24] LU Z D, YANG X, DAI J G . Shear behavior of RC beams strengthened with FRP grid reinforced engineered cementitious composites[C]//The Sixth Asia-Pacific Conference on FRP in Structures (APFIS2017). Singapore: International Institute for FRP in Construction (IIFC), 2017: 1-5. [25] BLANKSVARD T, TALJSTEN B, CAROLIN A. Shear strengthening of concrete structures with the use of mineral-based composites[J]. Journal of Composites for Construction,2009,13(1):25-34. doi: 10.1061/(ASCE)1090-0268(2009)13:1(25)