Study On Interface Problems Of FRP Reinforced Concrete Structures

In recent years, the use of beams and columns of FRP reinforced concretebecome a popular way in the field of building reinforcement. Therefore the failuremechanism of FRP bending and shear strengthening has become the key researchcontent in this field. In theoretical research, the full range behavior ofpropagation of interfacial debonding between the FRP and the concrete andinterfacial bond slip relationship have been of intriguing interest. This papermainly focuses on some key issues of the two aspects.The highlights and main contributions of this paper include:1．Bilinear local bond-slip law is employed to study full range debondingbehavior of the FRP-concrete interface for the pull-pull adhesive joints. The factorsinfluence the interfacial debonding process, such as different geometry materialparameters and constitutive relation parameters are analyzed in detail. Based onabove results, a clear classification of the process of interfacial debonding has beenprovided, and each kind of interfacial debonding process is studied stage by stage.The full range load-displacement responses are derived for different loading stages.Analytical expressions of FRP-concrete interface slip distribution, shear stressdistribution and FRP normal stress for each stage are presented.2．A clear classification of the cases that involves the unloading problem oflocal bond-slip law is made, and two confusable unloading forms (one is inbond-slip law and another in load-displacement response during loading) havebeen distinguished. Secant unloading is adopted to study interface unloading behavior for the pull-push adhesive joints, analytical solutions for the interface slipdistrubition, shear stress distrubition and FRP normal stress are presented. Also,unloading problem existed in portion of the full range load-displacement curveunder exponential softening law has been discussed; the effect caused by unloading(damage) has been studied through the finite element method. A finite elementnumerical example is also presented to explore the problem of cyclic loading.3. Based on the above work, a theoretical study on the process of middlecrack induced extension when the FRP-concrete interface is in shear reinforcementhas been made. According to the different bond length distribution on each side ofthe crack, crack propagating is classified into certain different types. The widthchange of crack and the normal stress distribution of FRP plate, and the damageevolution process of the interface for each type have been analysed in detail.4. The corresponding numerical examples are provided for the above eachpart of theoretical studies, and which have been also compared with thecorresponding finite element results. Advantages and disadvantages of the finiteelement method are examined when dealing with these issues.The above research will help better to understand some key factors of thestudy for FRP strengthened concrete structures, and the first part of this paper canbe easily extended to the research of the composite tubular structure which is intension or torsion. The third part of the paper can easily be extended to the researchfor the process of the middle crack propagation exiting in FRP-concrete flexuralstrengthening. Although the analytical solution cannot be obtained for theunloading of exponential softening law, we can consult the work of the second part of this paper and the difficulties can still be overcome through programming. Theresearch of this paper also provides some ideas for some other problems of theapplications of FRP reinforcement. At the same time, it also helps to developtheoretical research in the field of FRP reinforced concrete in the future.