Plate End Debonding Research Articles

Investigation on Intermediate Crack Induced Debonding Failure of FRP Laminates in Flexurally FRP-Strengthened RC Beams

Debonding failure is commonly observed in FRP-strengthened RC beams. It can be classified into two types: plate end debonding and intermediate crack induced debonding. Intermediate crack induced debonding is the main failure mode in FRP-strengthened RC beams.There is no specialized experiment study on this failure mode. To investigate intermediate crack induced debonding failure of FRP-strengthened reinforced concrete beams, 9 CFRP-strengthened reinforced concrete beams were tested. Based on the investigation of the strain in the FRP laminates, the width of the main crack and tributary crack, as well as the phenomena of the test beams, the whole debonding process can be separated into three stages: initial debonding stage, stable debonding stage, and the final debonding failure. The fundamental reason of intermediate crack indued debonding are the opening-up of intermediate crack and the flexural deformation induced high interfacial shear stress and peeling stress. When the principal tension stress acting on the concrete substrate exceeded the tension stress of concrete, the CFRP laminate would debond from the concrete substrate.

Premature failures in plate bonded strengthened RC beams with an emphasis on premature shear: A review

The aim of the present study is to review the performance of plate bonded flexurally strengthened reinforced concrete beams. This paper also describes the methods and materials used for flexural and shear strengthening of reinforced concrete beams and weaknesses of plate bonded systems. The plate bonding method often has some serious premature debonding failure which can be classified as plate end debonding (end peeling), tension delamination and premature shear failure due to insufficient shear reinforcement. Premature failures must be prevented in order to utilize the full flexural capacity of flexural strengthened reinforced concrete beams. Premature shear failure is one of the major concerns of the flexurally strengthened reinforced concrete (RC) beams. Hence, proper design of external shear strengthening system is required for eliminating premature shear failure of flexurally strengthened RC beams. The review focuses on the possible model and design guideline available in the literature for eliminating premature failures. The paper also discusses a probable approach to eliminate premature shear.

Linear Elastic Fracture Mechanics Approach to Plate End Debonding in Rectilinear and Curved Plated Beams

This paper proposes a linear elastic fracture mechanics approach for the prediction of plate end debonding in rectilinear and curved plated beams. The analytical model results in simple equations, suitable for immediate design use. The load-deflection curve of a plated beam, from the onset of debonding up to the complete separation of the plate, is obtained by controlling the length of the interfacial debonding crack. Its shape clearly shows that snap-back or snap-through instabilities may arise when the beam is loaded under displacement or force control. Analytical predictions are also compared with finite element results based on an interfacial cohesive crack model. It is shown that the predictions of the proposed analytical model match closely the numerical solution, provided that an effective crack length accounting for the size of the fracture process zone is used in the calculations.

Debonding Analysis along a Softening FRP-Concrete Interface between Two Adjacent Cracks in Plated Beams

External bonding of fibre reinforced polymer (FRP) composites has become a common way for strengthening concrete members. The performance of the interface between FRP and concrete is one of the key factors affecting the behaviour of the strengthened structure. For this FRP-concrete structure, there are two types of debonding failures: plate end debonding and intermediate crack (IC) induced debonding. This paper presents an analytical solution for the second type debonding failures in FRP-concrete bonded joint model where the FRP plate is subject to tension at both ends. Both the strengthened beam and strengthening FRP are modeled as two linearly elastic Euler–Bernoulli beams bonded together through a thin adhesive layer. The debonding process of the FRP–concrete interface is discussed in detail, and closed-form solutions of bond slip, interface shear stress, and axial force of FRP in different stages are obtained. Parametric studies are further carried out to investigate the effect of the thickness of adhesive layer on the bond behavior of FRP–concrete interface.

Simple General Solution for Interfacial Stresses in Plated Beams

The flexural strength of a reinforced concrete, metallic or timber beam can be increased by bonding a thin plate, made of steel or fiber-reinforced polymer, to its tension face. A main failure mode of such plated beams involves debonding of the plate end from the beam and such plate-end debonding depends strongly on the interfacial stresses between the beam and the plate. Consequently, many analytical solutions have been developed for the interfacial stresses of specific plated beam problems, with almost all of them being for simply supported plated straight beams of constant section subjected to simple loadings. The existing analytical solutions are therefore neither general enough nor simple enough for direct exploitation in assessing the risk of plate-end debonding failure. This paper corrects this deficiency by presenting a simple, accurate yet general solution for interfacial stresses. The solution is applicable to plated beams of all geometric (e.g., curved beams), sectional (e.g., tapered beams), loading (e.g., a linearly varying distributed load), and boundary conditions (e.g., continuous beams). The accuracy of the solution is demonstrated through comparisons with finite element results. The paper also presents simple and accurate approximations for the peak values of interfacial shear and normal stresses at the plate end. In these approximate expressions, only the sectional forces and properties of the plate end section are involved, which greatly facilitates their direct exploitation in predicting debonding failure.

Formula omitted]-Version nonlinear analysis of RC beams and slabs strengthened with externally bonded plates

The p-version nonlinear RC finite element model has been used to analyze the nonlinear behavior of RC beams and slabs as well as RC beams and slabs strengthened by externally bonded steel or FRP plates. The numerical approach is based on the p-version shell element, including the theory of anisotropic laminated composites considering geometric and material nonlinearities. In the nonlinear formulation of this model, the total Lagrangian formulation is adopted with large deflections and moderate rotations being accounted for in the sense of von Karman hypothesis. The material model is based on the Kupfer's yield criterion, hardening rule, crushing condition and plate-end debonding strength model. Integrals of Legendre polynomials are used for shape functions with p-level varying from 1 to 10. The Gauss–Lobatto numerical quadrature is applied to calculate the stresses at the nodal points instead of Gauss points. The validity of the proposed p-version of the finite element model for RC beams and slabs as well as externally strengthened RC beams and slabs is demonstrated in terms of ultimate load, effect of reinforcement, failure mode, stress in reinforcing steel, convergence characteristics, debonding failure at plate end, and compared with available experimental and numerical results.

FRP-to-concrete interfaces between two adjacent cracks: Theoretical model for debonding failure

External bonding of fibre reinforced polymer (FRP) composites has become a popular technique for strengthening concrete structures all over the world. The performance of the interface between FRP and concrete is one of the key factors affecting the behaviour of the strengthened structure. Existing laboratory research has shown that the majority of reinforced concrete (RC) beams strengthened with a bonded FRP soffit plate fail due to debonding of the plate from the concrete. Two types of debonding failures have been commonly observed: plate end debonding and intermediate crack induced debonding. In order to understand and develop methods to predict such debonding failures, the bond behaviour between concrete and FRP has been widely studied using simple shear tests on FRP plate/sheet-to-concrete bonded joints and a great deal of research is now available on the behaviour of these bonded joints. However, for intermediate crack induced debonding failures, the debonding behaviour can be significantly different from that observed in a simple shear test. Among other factors, the most significant difference may be that the FRP plate between two adjacent cracks is subject to tension at both cracks. This paper presents an analytical solution for the debonding process in an FRP-to-concrete bonded joint model where the FRP plate is subject to tension at both ends. A realistic bi-linear local bond-slip law is employed. Expressions for the interfacial shear stress distribution and the load–displacement response are derived for different loading stages. The debonding process is discussed in detail. Finally, results from the analytical solution are presented to illustrate how the bond length affects the behaviour of such bonded joints. While the emphasis of the paper is on FRP-to-concrete joints, the analytical solution is equally applicable to similar joints between thin plates of other materials (e.g. steel and aluminium) and concrete.

Shear-Bending Interaction in Debonding Failures of FRP-Plated RC Beams

Fibre reinforced polymer (FRP) plates can be bonded to the tension face of a reinforced concrete (RC) beam to increase its flexural capacity. Many studies have reported premature failure by debonding of the FRP plate before the ultimate flexural capacity of the plated section is reached, and the most commonly reported debonding failure mode occurs at or near the plate end. This paper presents the results of an experimental investigation into the interaction between shear force and bending moment at the plate end at debonding for FRP plated beams by varying the length of plate. The experimental results are compared with a plate end debonding strength model recently proposed by the authors in which this interaction is ignored. A bi-linear approximation is then proposed to describe the interaction between the shear force and the bending moment at the plate end at debonding based on the present results. The effect of U strip end anchorage, used to delay or prevent plate end debonding, is also assessed in this study but it is shown that U strip end anchorage provides only limited strength enhancement.

FRP-strengthened RC beams. II: assessment of debonding strength models

Reinforced concrete (RC) beams strengthened in flexure by the bonding of a fiber reinforced polymer (FRP) plate to the tension face are susceptible to brittle debonding failures. Such failures commonly initiate at or near one of the plate ends at a load below that to achieve flexural failure of the plated section. For a successful design of flexural strengthening using FRP composites, it is important to be able to predict such plate end debonding failures. In the first of these two companion papers, 12 plate end debonding strength models have been reviewed and summarized (Engng Struct 24(4) (2002) 385–395). The aim of the present paper is to provide a comprehensive assessment of the strengths and weaknesses of all the 12 models. To this end, a large test database containing the test results of 59 beams reported to have failed by plate end debonding is first presented. This database was carefully constructed from an extensive survey of the published literature. Both statistical and graphical comparisons between test results and the predictions of the debonding strength models are next presented. A new simple debonding strength model which is superior to existing models is also proposed.