内嵌FRP筋加固混凝土梁的抗剪性能研究

Study on Shear Behavior of RC Beams Strengthened with NSM FRP Bars

目的探究内嵌FRP筋加固混凝土梁的抗剪性能和剪切延性性能,建立加固梁的抗剪承载力计算公式,为加固梁抗剪加固的应用提供理论依据.方法对7根内嵌FRP筋加固混凝土梁和2根对比梁进行抗剪性能试验,分析其破坏模式;研究其荷载-挠度关系曲线、荷载-FRP筋、箍筋应变关系曲线,分析斜截面应力重分布现象以及剪切延性性能;基于拱形桁架模型,引入关键系数,建立加固梁的受剪承载力计算公式.结果加固梁的抗剪承载力提高了近30%;发生剪切破坏各加固梁的剪切延性系数与对比梁BS2剪切延性系数相比的平均比值为1.167,剪切延性有所改善;加固梁斜截面出现了2次应力重分布,分别是斜裂缝出现时和箍筋屈服时;将已有文献剪切破坏加固梁的抗剪承载力试验值与笔者建立的加固梁抗剪计算公式的计算值进行对比,吻合较好.结论内嵌FRP筋加固技术能够提高梁的整体刚度和抗剪承载力,有效地延缓斜裂缝的开展,减小斜裂缝的宽度,提高混凝土骨料间的咬合作用,从而改善加固构件的受力情况及变形能力.

The aim of this paper is to investigate the shear behavior and shear ductility,and to establish the shear bearing capacity formula of RC beam strengthened with NSMFRP bars,which provides theory basis for the engineering application of RC beam in shear strengthening. The total of 7 RC beams strengthened with NSMFRP bars and 2 control beams in shear were conducted out. The failure mode,load-displacement relationship,load-strain of FRP bars and stirrup relationship,stress redistribution on inclined section and shear ductility behavior are studied. Based on the arch truss model,the key coefficient is introduced to establish the formula of shear bearing capacityof the strengthened beam. The results showthat the shear capacity of the strengthened beam increase by 30%,compared to the control beam. The average ratio of the shear ductility coefficient of the strengthened beam for the shear failure to the control beam BS2 is 1. 167. It shows the improvement of shear ductility to some extent. When the diagonal crack appears and the yielding of the stirrup,the stress redistribution on inclined section occurs. The ratio of the test results of the shear bearing capacity from the previous papers to the calculated results from this paper is in good agreement. The NSMFRP bars strengthening technology can improve the overall stiffness and shear capacity,effectively delay the propagation of diagonal cracks,reduce the crack width,and enhance aggregate interlock behavior of concrete. Consequently,the stressed state and deformation capacity of the strengthening component are improved.