INTRODUCTIONExtensive research has been conducted on the strengthening of reinforced concrete (RC) beams with externallybonded fibre reinforced polymer (FRP) composites (ACI 2002, Chaallal et al. 1998, Chen and Teng 2001a, b,Chen and Teng 2003a, b, Concrete Society 2004, fib 2001, ISIS 2001, JSCE 2000, Khalifa et al. 1998, Maeda etal. 1998, Taljsten 2003, Teng et al. 2002, 2003, Triantafillou 1998). RC beams can be shear-strengthenedthrough complete wrapping, U jacketing or side bonding (bonding of FRP on the beam sides only). The mainshear failure modes of shear-strengthened RC beams are FRP rupture and debonding (Teng et al. 2002, 2003).In both failure modes, the stress (or strain) distribution in the FRP at the ultimate limit state is non-uniform andis a key factor influencing the contribution of the FRP to the shear capacity of the beam for all threestrengthening schemes (Chen and Teng 2003a,b). Based on a number of simple but rational assumptions, Chenand Teng (2003a,b) proposed methods for predicting the maximum values of the FRP stress and the stressdistribution factors for both failure modes.Experimental research shows that most side-bonded beams fail due to debonding of the FRP from the concrete.This paper presents a simple theoretical study on the stress distribution in the FRP along the critical shear crackat debonding failure in side-bonded beams. A recently developed FRP-to-concrete bond-slip model (Lu et al.2005a) was used in this study. Several idealised crack width variations, which are closely related to the FRP slipfield along the critical shear crack, are investigated. The results are compared with Chen and Teng’s (2003a)simple predictive model. For convenience of description, the bonded FRP reinforcement is assumed to be in theform of strips, with a continuous sheet being a special case or a smeared equivalent representation of strips.Depending on the context, either “strips” or “sheets” may be used to refer to the bonded FRP reinforcement.EXISTING SHEAR STRENGTH MODELS FOR DEBONDING FAILURESA number of models for the shear strength of FRP-strengthened RC beams have been proposed for design use(Chaallal et al. 1998, Khalifa et al. 1998, Triantafillou 1998, Taljsten 2003, Chen and Teng 2003a,b). In most ofthese proposals, the shear strength of an FRP-strengthened RC beam Vn is evaluated by assuming that thecontributions of the concrete Vc, the steel shear reinforcement Vs, and the bonded FRP reinforcement Vf areadditive, i.e.Vn = Vc Vs Vf (1)Because it is usually proposed that Vc and Vs should be calculated according to provisions in existing designcodes, the main differences between the available proposals lie in the evaluation of the FRP contribution Vf.Steel stirrups have a small elastic strain limit but excellent ductility, so all stirrups intersected by the criticalshear crack can reach their yield stress at the shear failure of the RC beam as a result of stress re-distribution.This means that their yield strength is

(本人所学非土木专业，望业内人士多提意见)

前言：研究人员对于外部粘贴玻璃纤维增强聚合物(FRP)复合材料的钢筋混凝土(RC)梁加固已经进行了大量的研究(ACI 2002, Chaallal 等人. 1998, 陈 和 藤 2001a, b, 2003a, b, 陈 和 藤，混凝土学会，2004, fib 2001, ISIS 2001, JSCE 2000, Khalifa 等人. 1998, Maeda 等人. 1998, Taljsten 2003, 藤 等人. 2002, 2003, Triantafillou 1998)。通过完全包裹、加U型箍和侧面粘贴（FRP只粘贴梁的侧面），RC梁可以得到抗剪加固。RC梁抗剪加固破坏的主要形式是FRP断裂破坏和剥离破坏（藤等人，2002, 2003）。所以出现上面两种破坏形式，主要是在极限状态下FRP应力（或应变） 分布不均所致，也是三种加固设计中影响FRP提高钢筋混凝土梁抗剪能性的主要因素(陈 和 藤 2003a,b)。 根据一些简单而合理的假设， 陈 和 藤( 2003a,b)就两种破坏形式提出了若干方法来预测FRP最大应力值和应力分布系数。试验研究显示多数FRP侧面粘贴的混凝土梁的破坏主要由FRP从混凝土中剥离所致，本文针对FRP沿侧面粘贴梁剥离破坏的关键裂缝，就应力分布进行了简明的理论性研究。研究中使用了近期研发的FRP—混凝土粘贴滑脱模型(鲁，等人，.2005a)，对几种理想化的裂缝宽度变化进行了调查，因为裂缝宽度变化与FRP沿关键剪切裂缝的滑脱范围密切相关，并将调查结果与陈 和 藤 （2003a）的简单的预测模型进行了对比。为便于描述，假设FRP粘贴加固呈条带状，用一延续的板材形成一种特殊场景或用一种弥散的等效品代表条带状。根据文章的前后关系，或用带状物或用板材来说明FRP的粘贴加固。在“关于剥离破坏现有抗剪强度模型”一文中，研究人员提出了FRP增强RC梁抗剪强度的几种模型用于工程设计(Chaallal 等人. 1998, Khalifa 等人. 1998, Triantafillou 1998, Taljsten 2003, 陈 和 藤 2003a,b)。大多数建议都对FRP增强RC梁抗剪强度Vn进行了评价，评价方法是假设混凝土为Vc、抗剪钢筋为Vs、FRP粘贴加固为Vf，三种作用相加等于Vn，即Vn = Vc ＋Vs＋Vf (1)。因为在一般情况下研究人员建议要根据现有设计规范的条款来评价Vc和Vs，因此，可用建议的主要差异在于评价FRP的作用Vf。由于钢箍应变限制较小且韧性极佳，因此， RC梁在受剪破坏的条件下，所有与关键受剪裂缝相交的钢箍因应力二次分布均可达到屈服应力，这意味着钢箍的屈服强度 。。。。