混锚预应力U形碳纤维条带抗剪加固混凝土梁试验研究
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摘要
研发钢筋混凝土梁抗剪加固用U形纤维增强复材(FRP)条带的预应力系统,提出一种预应力U形条带端锚与黏贴并用(简称混锚)的抗剪加固方法。完成了1根未加固、7根采用U形碳纤维(CFRP)条带进行抗剪加固的矩形截面梁剪切试验,加固梁中1根为纯黏贴、6根为混锚预应力。结果表明:混锚预应力加固在抑制主斜裂缝开展、延缓箍筋屈服和提高箍筋塑性利用率等方面的表现均优于纯黏贴加固,能够防止FRP端部剥离并实现拉断破坏,大幅度提高纤维强度利用率,显著提高梁的抗剪承载力,最大提升率达92%。预应力和配纤率的大小对抗剪加固效果有较明显影响,其他条件相同时,预应力越大或配纤率越高,加固梁综合性能越好。建议了混锚预应力U形CFRP有效应变的计算公式,用于预测剪切破坏时CFRP的贡献和加固梁的承载能力,与试验结果符合良好,可供工程应用参考。
U-strips of fiber reinforced polymer(FRP) are usually used for shear strengthening of reinforced concrete beams. A novel prestressing system with hybrid anchorage is proposed, in which the prestressed FRP is bonded to beam surfaces and the ends are anchored by interlocking. Eight rectangular beams were tested to validate the feasibility of the new method, including one control beam, one strengthened with bonded CFRP U-strips and six strengthened with hybrid-anchored and prestressed CFRP U-strips. The results show that the proposed prestressing method performs much better than externally bonding in the aspects of restraining the propagation of diagonal cracks and improving the strain behavior of steel stirrups. The end-debonding of CFRP can be shifted to rupture failure, the fiber-strength utilization can be significantly enhanced, and the shear capacity of RC beam can be increased with the maximum increase rate about 92%. The strengthening effect is related to the area ratio and the prestress of CFRP. Raising area ratio or prestress value is helpful to improve the comprehensive performance of the strengthened beams. Furthermore, a formula for calculating the effective strain of prestressed CFRP was proposed and then used to calculate shear capacities of the strengthened beams. The calculated capacities are all in good agreement with the test results, indicating that the formula can serve as a rational reference for engineering application.
U-strips of fiber reinforced polymer(FRP) are usually used for shear strengthening of reinforced concrete beams. A novel prestressing system with hybrid anchorage is proposed, in which the prestressed FRP is bonded to beam surfaces and the ends are anchored by interlocking. Eight rectangular beams were tested to validate the feasibility of the new method, including one control beam, one strengthened with bonded CFRP U-strips and six strengthened with hybrid-anchored and prestressed CFRP U-strips. The results show that the proposed prestressing method performs much better than externally bonding in the aspects of restraining the propagation of diagonal cracks and improving the strain behavior of steel stirrups. The end-debonding of CFRP can be shifted to rupture failure, the fiber-strength utilization can be significantly enhanced, and the shear capacity of RC beam can be increased with the maximum increase rate about 92%. The strengthening effect is related to the area ratio and the prestress of CFRP. Raising area ratio or prestress value is helpful to improve the comprehensive performance of the strengthened beams. Furthermore, a formula for calculating the effective strain of prestressed CFRP was proposed and then used to calculate shear capacities of the strengthened beams. The calculated capacities are all in good agreement with the test results, indicating that the formula can serve as a rational reference for engineering application.
引文
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[5]Zhang H W,Smith S T,Kim S J.Optimisation of carbon and glass FRP anchor design[J].Construction and Building Materials,2012,32:1-12
[6]Micelli F,Annaiah R H,Nanni A.Strengthening of short shear span reinforced concrete T joists with fiber-reinforced plastic composites[J].Journal of Composites for Construction,2002,6(4):264-271
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[11]Kesse G,Lees J M.Experimental behavior of reinforced concrete beams strengthened with prestressed CFRPshear straps[J].Journal of Composites for Construction,2007,11(4):373-383
[12]Hoult N A,Lees J M.Efficient CFRP strap configurations for the shear strengthening of reinforced concrete T-beams[J].Journal of Composites for Construction,2009,13(1):45-52
[13]彭刚.预应力碳纤维布加固钢筋混凝土梁受剪性能的试验研究[D].郑州:郑州大学,2005(Peng Gang.Astudy on shear properties of RC beams strengthened with prestressed carbon fiber sheet[D].Zhengzhou:Zhengzhou University,2005(in Chinese))
[14]程东辉,荣威,周威.预应力CFRP布加固负载混凝土梁受剪性能试验[J].哈尔滨工业大学学报,2011,43(12):143-148(Cheng Donghui,Rong Wei,Zhou Wei.Experimental research of shear resistance performance on loaded concrete beam reinforced with prestressed CFRP sheet in diagonal section[J].Journal of Harbin Institute of Technology,2011,43(12):143-148(in Chinese))
[15]周朝阳,周奥利,周欣涛.柔性片状材料绕杆自锁的方法:中国,ZL201010269384[P].2010-12-29
[16]周朝阳,周奥利,周欣涛.柔性片状材料平行杆式锚固装置及方法:中国,ZL2010105166838[P].2011-01-19
[17]魏少雄.自锚式U形碳纤维布预应力抗剪加固钢筋混凝土T梁试验研究[D].长沙:中南大学,2009(Wei Shaoxiong.Experimental research of prestressed reinforced concrete shear T-beam using self-anchorage CFRP of U shape[D].Changsha:Central South University,2009(in Chinese))
[18]刘君,周朝阳,韩殿牧原,等.抗剪加固用U形纤维布条带预应力系统设计及试验[J].湖南大学学报:自然科学版,2016,43(11):47-54(Liu Jun,Zhou Chaoyang,Han Dianmuyuan,et al.Design and experiment study of prestressing system for U-shaped FRP sheet in shear strengthening[J].Journal of Hunan University:Natural Sciences,2016,43(11):47-54(in Chinese))
[19]周朝阳,赵波涌,刘君,等.无黏结预应力U形CFRP加固混凝土梁抗剪试验[J].哈尔滨工业大学学报,2017,49(6):15-20(Zhou Chaoyang,Zhao Boyong,Liu Jun,et al.Shear tests of RC beams strengthened with unbounded prestressed U-strips of CFRP[J].Journal of Harbin Institute of Technology,2017,49(6):15-20(in Chinese))
[20]Zsutty T.Shear strength prediction for separate catagories of simple beam tests[J].ACI Structural Journal,1971,68(2):138-143
[21]谭壮,叶列平.纤维复合材料布加固混凝土梁受剪性能的试验研究[J].土木工程学报,2003,36(11):12-18(Tan Zhuang,Ye Lieping.Experimental research on shear capacity of RC beam strengthened with externally bonded FRP sheets[J].China Civil Engineering Journal,2003,36(11):12-18(in Chinese))
[2]周朝阳,谭磊,程小念.FRP抗剪加固钢筋混凝土梁研究综述[J].建筑科学与工程学报,2011,28(2):1-7(Zhou Chaoyang,Tan Lei,Cheng Xiaonian.Review of research on reinforced concrete beams shearstrengthened with FRP[J].Journal of Architecture and Civil Engineering,2011,28(2):1-7(in Chinese))
[3]冯鹏,陆新征,叶列平.纤维增强复合材料建设工程应用技术--试验?理论与方法[M].北京:中国建筑工业出版社,2011(Feng Peng,Lu Xinzheng,Ye Lieping.Application of fiber reinforced polymer in construction:experiment,theory and methodology[M].Beijing:China Architecture&Building Press,2011(in Chinese))
[4]Kim S J,Smith S T.Pullout strength models for FRPanchors in uncracked concrete[J].Journal of Composites for Construction,2010,14(4):406-414
[5]Zhang H W,Smith S T,Kim S J.Optimisation of carbon and glass FRP anchor design[J].Construction and Building Materials,2012,32:1-12
[6]Micelli F,Annaiah R H,Nanni A.Strengthening of short shear span reinforced concrete T joists with fiber-reinforced plastic composites[J].Journal of Composites for Construction,2002,6(4):264-271
[7]Khalifa A,Alkhrdaji T,Nanni A,et al.Anchorage of surface mounted FRP reinforcement[J].Concrete International,1999,21(10):49-54
[8]Ceroni F,Pecce M,Matthys S,et al.Debonding strength and anchorage devices for reinforced concrete elements strengthened with FRP sheets[J].Composites:Part B-Engineering,2008,39(3):429-441
[9]Kalfat R,Al-Mahaidi R,Smith S.Anchorage devices used to improve the performance of reinforced concrete beams retrofitted with FRP composites:state-of-the-art review[J].Journal of Composites for Construction,2013,17(1):14-33
[10]Grelle S V,Sneed L H.Review of anchorage systems for externally bonded FRP laminates[J].International Journal of Concrete Structures and Materials,2013,7(1):17-33
[11]Kesse G,Lees J M.Experimental behavior of reinforced concrete beams strengthened with prestressed CFRPshear straps[J].Journal of Composites for Construction,2007,11(4):373-383
[12]Hoult N A,Lees J M.Efficient CFRP strap configurations for the shear strengthening of reinforced concrete T-beams[J].Journal of Composites for Construction,2009,13(1):45-52
[13]彭刚.预应力碳纤维布加固钢筋混凝土梁受剪性能的试验研究[D].郑州:郑州大学,2005(Peng Gang.Astudy on shear properties of RC beams strengthened with prestressed carbon fiber sheet[D].Zhengzhou:Zhengzhou University,2005(in Chinese))
[14]程东辉,荣威,周威.预应力CFRP布加固负载混凝土梁受剪性能试验[J].哈尔滨工业大学学报,2011,43(12):143-148(Cheng Donghui,Rong Wei,Zhou Wei.Experimental research of shear resistance performance on loaded concrete beam reinforced with prestressed CFRP sheet in diagonal section[J].Journal of Harbin Institute of Technology,2011,43(12):143-148(in Chinese))
[15]周朝阳,周奥利,周欣涛.柔性片状材料绕杆自锁的方法:中国,ZL201010269384[P].2010-12-29
[16]周朝阳,周奥利,周欣涛.柔性片状材料平行杆式锚固装置及方法:中国,ZL2010105166838[P].2011-01-19
[17]魏少雄.自锚式U形碳纤维布预应力抗剪加固钢筋混凝土T梁试验研究[D].长沙:中南大学,2009(Wei Shaoxiong.Experimental research of prestressed reinforced concrete shear T-beam using self-anchorage CFRP of U shape[D].Changsha:Central South University,2009(in Chinese))
[18]刘君,周朝阳,韩殿牧原,等.抗剪加固用U形纤维布条带预应力系统设计及试验[J].湖南大学学报:自然科学版,2016,43(11):47-54(Liu Jun,Zhou Chaoyang,Han Dianmuyuan,et al.Design and experiment study of prestressing system for U-shaped FRP sheet in shear strengthening[J].Journal of Hunan University:Natural Sciences,2016,43(11):47-54(in Chinese))
[19]周朝阳,赵波涌,刘君,等.无黏结预应力U形CFRP加固混凝土梁抗剪试验[J].哈尔滨工业大学学报,2017,49(6):15-20(Zhou Chaoyang,Zhao Boyong,Liu Jun,et al.Shear tests of RC beams strengthened with unbounded prestressed U-strips of CFRP[J].Journal of Harbin Institute of Technology,2017,49(6):15-20(in Chinese))
[20]Zsutty T.Shear strength prediction for separate catagories of simple beam tests[J].ACI Structural Journal,1971,68(2):138-143
[21]谭壮,叶列平.纤维复合材料布加固混凝土梁受剪性能的试验研究[J].土木工程学报,2003,36(11):12-18(Tan Zhuang,Ye Lieping.Experimental research on shear capacity of RC beam strengthened with externally bonded FRP sheets[J].China Civil Engineering Journal,2003,36(11):12-18(in Chinese))