• Advances in concrete construction
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• v.7 no.3
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• pp.151-166
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• 2019

This paper introduces a new efficient analytical method, based on shear deformations obtained with 2D elasticity theory approach, to perform an explicit closed-form solution for calculation the interfacial shear and normal stresses in plated RC beam. The materials of plate, necessary for the reinforcement of the beam, are in general made with fiber reinforced polymers (Carbon or Glass) or steel. The experimental tests showed that at the ends of the plate, high shear and normal stresses are developed, consequently a debonding phenomenon at this position produce a sudden failure of the soffit plate. The interfacial stresses play a significant role in understanding this premature debonding failure of such repaired structures. In order to efficiently model the calculation of the interfacial stresses we have integrated the effect of shear deformations using the equilibrium equations of the elasticity. The approach of this method includes stress-strain and strain-displacement relationships for the adhesive and adherends. The use of the stresses continuity conditions at interfaces between the adhesive and adherents, results pair of second-order and fourth-order coupled ordinary differential equations. The analytical solution for this coupled differential equations give new explicit closed-form solution including shear deformations effects. This new solution is indented for applications of all plated beam. Finally, numerical results obtained with this method are in agreement of the existing solutions and the experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.177-180
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• 2005

The specified tensile strength provided by the manufacturer is determined on the basis of the reliable lower limit ($X-3{\sigma}$ : X=average tensile strength, $\sigma$=standard deviation) obtained from the material test results. Most of these data, however, are based on the test results of 1 layer of FRP sheet. Also, the partial strength reduction factor for strengthening RC members with FRP is based on the small-scale model tests. But, the failure mechanisms of small-scale model tests are reported to be different from those of the full-scale tests. This paper present the test results of full-scale RC beams strengthened with multi-layer GFRP sheets up to 3 layer as well as the material tests. From the material tests, it was observed that the average tensile strengths of GFRP sheets are decreased as the number of layer are increased. Also the premature debonding failure of RC beams strengthened with multi-layer GFRP sheets are observed in inverse proportion to the number of GFRP sheets

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.04a
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• pp.365-372
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• 2004

A new finite element model will be presented to analyze the nonlinear behavior of not only RC beams and slabs, but also RC beams strengthened by a patch repair. The numerical approach is based on the p-version degenerate shell element including theory of anisotropic laminated composites, theory of materially and geometrically nonlinear plates. 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 hardening rule, crushing condition, plate-end debonding strength model and so on. 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 finite element model is demonstrated through several numerical examples for the load-deflection curves, the ultimate loads, and the failure modes of reinforced connote slabs and RC beams bonded with steel plates or FRP plates compared with available experimental and numerical results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.375-387
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• 2004

A new finite element model will be presented to analyze the nonlinear behavior of RC beams and slabs strengthened by a patch repair. The numerical approach is based on the p-version degenerate shell element including theory of anisotropic laminated composites, theory of materially and geometrically nonlinear plates. 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 hardening rule, crushing condition, plate-end debonding strength model and so on. 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 nonlinear finite element model is demonstrated through the load-deflection curves, the ultimate loads, and the failure modes of RC beams or slabs bonded with steel plates or FRP plates compared with available result of experiment and other numerical methods.

• Structural Engineering and Mechanics
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• v.72 no.4
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• pp.409-420
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• 2019

The paper presents the results of an experimental and numerical programme to characterize the behaviour of steel beams reinforcement by composite plates. Important failure mode of such plated beams is the debonding of the composite plates from the steel beam due to high level of stress concentration in the adhesive at the ends of the composite plate. In this new research, an experimental and numerical finite element study is presented to calculate the stresses in the sika carbodur and sika wrap reinforced steel beam under mechanical loading. The main objective of the experimental program was the evaluation of the force transfer mechanism, the increase of the load capacity of the steel beam and the flexural stiffness. It also validated different analytical and numerical models for the analysis of sika carbodur and sika wrap reinforced steel beams. In particular, a finite element model validated with respect to the experimental data and in relation to the analytical approach is presented. Experimental and numerical results from the present analysis are presented in order to show the advantages of the present solution over existing ones and to reconcile debonding stresses with strengthening quality.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.1053-1064
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• 2005

The mechanical damage of concrete is normally attributed to the formation of microcracks and their propagation and coalescence into macroscopic cracks. This physical degradation is caused from progressive and hierarchical damage of the microstructure due to debonding and slip along bimaterial interfaces at the mesoscale. Their growth and coalescence leads to initiation of hairline discrete cracks at the mesoscale. Eventually, single or multiple major discrete cracks develop at the macroscale. In this paper, from this conceptual model of mechanical damage in concrete, the computational efforts were made in order to characterize physical cracks and how to quantify the damage of concrete materials within the laws of thermodynamics with the aid of interface element in traditional finite element methodology. One dimensional effective traction/jump constitutive interface law is introduced in order to accommodate the normal opening and tangential slips on the interfaces between different materials(adhesion) or similar materials(cohesion) in two and three dimensional problems. Mode I failure and mixed mode failure of various geometries and boundary conditions are discussed in the sense of crack propagation and their spent of fracture energy under monotonic displacement control.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.937-940
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• 2006

According to the analysis of tension failure mechanism of UHSC specimen, one modified model based on ACK model by the introduction of partial debonding energy of non-first cracks and by the application of steel fiber number on unit area is presented in this paper. It can be used to explain the evolution mechanism of multiple cracking and pseudo strain hardening of UHSC. From the numerical results, to increase steel fiber length and to reduce steel fiber diameter in some region all can reduce the fiber volume fraction with the same multiple cracks for economic design of UHSC.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.467-474
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• 2007

In this paper, a total of 13 beams with bonding, anchorage system, amount of prestressing and span length as variables of experiment were tested in flexural test and analyzed in finite element analysis; one control beam, two simplified FRP-boned beams, four prestressed FRP-unbonded beams and four prestressed FRP-bonded beams. Also, a nonlinear finite element analysis of beams in the flexural test is performed by DIANA program considered material nonlinear of concrete, reinforcement and the interfacial bond-slip model between concrete and CFRP plates. The failure mode of prestressed CFRP plated-beams is not debonding but FRP rupture. RC members strengthened with external bonded prestressed CFRP plates occurred 1st and 2nd debonding of the composite material. After the debonding of CFRP plates occurs in bonded system, behavior of bonded CFRP-plated beams change into that of unbonded CFRP-plated beams due to fix of the anchorage system. Also, It was compared flexural test results and analytical results of RC members strengthened with CFRF plates. The ductility of beams strengthened by CFRP plates with the anchorage system is considered high with the ductility index of above 3. Analysis results showed a good agreement with experiment results in the debonding load, yield load and ultimate load.

• Structural Engineering and Mechanics
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• v.56 no.6
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• pp.899-916
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• 2015

Upgrading or strengthening of existing reinforced concrete (RC) infrastructure is an emerging demand nowadays. Near Surface Mounted (NSM) technique is very promising approach for flexural strengthening of RC members. However, premature failure such as concrete cover separation failure have been a main concern in utilizing this technique. In this study, U-wrap end anchorage with carbon fiber reinforced polymer (CFRP) fabrics is proposed to eliminate the concrete cover separation failure. Experimental programs were conducted to the consequence of U-wrap end anchorage on the flexurally strengthened RC beams with NSM-steel. A total of eight RC rectangular beam specimens were tested. One specimen was kept unstrengthened as a reference; three specimens were strengthened with NSM-steel bars and the remaining four specimens were strengthened with NSM-steel bars and U-wrap end anchorage using CFRP fabrics. A 3D non-linear finite element model (FEM) was developed to simulate the flexural response of the tested specimens. It is revealed that NSM-steel (with and without end-anchors) significantly improved the flexural strength; moreover decreased deflection and strains compared with reference specimen. Furthermore, NSM-steel with end anchorage strengthened specimens revealed the greater flexural strength and improve failure modes (premature to flexure) compared with the NSM-steel without end anchorage specimens. The results also ensured that the U-wrap end anchorage completely eliminate the concrete cover separation failure.

• Advances in concrete construction
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• v.5 no.6
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• pp.625-638
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• 2017

The flexural behavior of Fiber reinforced polymer (FRP) sheets has gained much research interest in the flexural strengthening of reinforced concrete beams. The study on flexure includes various parameters like increase in strength of the member due to the externally bonded (EB) Fiber reinforced polymer, crack patterns, debonding of the fiber from the structure, scaling, convenience of using the fibers, cost effectiveness, etc. The present work aims to study experimentally about the reasons behind the failure due to flexure of an externally bonded FRP concrete beam. In the design of FRP-reinforced concrete structures, deflection control is as critical as much as flexural strength. A numerical model is created using Finite element (FEM) software and the results are compared with that of the experiment.