• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.442-448
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• 1997

An analytical method based on the nonlinear layered finite element method is developed to simulate the load-dsflection behavior of strengthened beams. Beams considered in this study are the ones strengthened either with external steel plate or Carbon Fiber Sheets(CFS) bonded to the overlay soffit. The theoretically obtained load-deflections and strains of the strengthened beams are compared to the corresponding experimental values. Parametric studies are, then. performed using the developed model to investigate the effects of design variables on the flexural behavior of the strengthened beams. Simply supported beams under monotonically increasing loads sre considered exclusively.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.283-286
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• 2005

The effectiveness of shear strengthening with glass fiber sheets on normal or low strength RC beams have been investigated experimentally. A design compressive strength of concrete of 13.5MPa has been planned considering the degradation state of the existing structure to be strengthened in this study. Also, concrete surface reinforcing agent was applied to increase bond capacity between concrete and GFRP sheets in case of low strength RC beams. Comparing the test results of low and normal strength beams strengthened with GFRP sheets indicated that total shear capacity of beams was decreased with concrete strength decreased, but the shear strengthening capacity of GFRP sheets are hardly affected by concrete strength. In addition, shear strengthening effects of RC beams strengthened with GFRP sheets can be estimated by $\rho_w{\cdot}f_w$ based on the maximum effective strain of FRP sheet proposed by ACI 440.2R recommendation.

• Steel and Composite Structures
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• v.20 no.2
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• pp.413-429
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• 2016

A theoretical method to predict the interfacial stresses in the adhesive layer of reinforced concrete beams strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) plate is presented. The analysis provides efficient calculations for both shear and normal interfacial stresses in reinforced concrete beams strengthened with composite plates, and accounts for various effects of Poisson's ratio and Young's modulus of adhesive. Such interfacial stresses play a fundamental role in the mechanics of plated beams, because they can produce a sudden and premature failure. The analysis is based on equilibrium and deformations compatibility approach developed by Tounsi. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both the reinforced concrete beam and bonded plate. The paper is concluded with a summary and recommendations for the design of the strengthened beam.

• Journal of the Korean Society for Railway
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• v.7 no.4
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• pp.319-325
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• 2004

In this study, analysis and design programs of bending of RC beams strengthened with fiber sheets are developed by using Visual Basic Language. The program consists two groups, ultimate strength method and nonlinear flexural analysis method. Ultimate strength method regards concrete compressive stress as a rectangular stress block and do not consider tensile stress of concrete and load-deflection curves. On the other hand, nonlinear flexural analysis considers tensile stress of concrete, load-deflection curves, state of stress distribution and failure strain of strengthening material. Also, the analysis method used in this study regards nonlinear flexural stress as compressive stress of concrete. This program can be a good tool for determining the bending strength of strengthened RC beams and estimating the amount of fiber sheets for practical use.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.69-80
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• 1999

The strengthening of reinforced concrete structures by externally bonded GFRP has become increasingly common in resent years. However the analysis and design method for GFRP plate strengthening of RC beams is not well established yet. The purpose of present paper is, therefore, to define the failure mechanism and failure behavior of strengthened RC beam using GFRP and then to propose a resonable method for the calculation of interface debonding load for those beams. From the experimental results of beams strengthened by GFRP, the influence of length and thickness, width of plate on the interfacial debonding failure behavior of beam is studied and, on the basis of test results, the semi-empirical equation to predict debonding load is developed. The proposed theory based on nonlinear analysis and critical flexural crack width, predicts relatively well the debonding failure load of test beams and may be efficiently used in the analysis and design of strengthened RC beams using GFRP.

• KCI Concrete Journal
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• v.12 no.1
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• pp.69-77
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• 2000

The reinforced concrete(RC) flexural members strengthened with steel plate/CFS at soffit have initial stresses and strains in reinforcements and concrete caused by the service loads at the time of retrofitting works. These initial residual stresses and strains of strengthened beams may affect the flexural performance of the rehabilitated beams. The objective of this study is to evaluate and verify the effectiveness of rehabilitation by external bonded steel plates and CFS to the tension face of the beams under three conditions of pre-loading. Thirteen beam specimens are tested and analyzed. Main test parameters are pre-loading conditions, strengthening materials and reinforcement ratio of specimens. The effect of test parameters on the strengthened beams is analyzed from the maximum load capacity, load-deflection relationship, state of stress of the materials. crack propagation phase, and failure modes. Both test results and design formulas of ACI Code provisions are compared and evaluated.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.173-176
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• 2006

The one of the commonly reported failure mode of the RC beam strengthened with FRP was caused by the separation of the concrete cover, so called delamination. Therefore, ACI440 recommended that concrete cover delamination can be prevented in strengthened beams if bond length of FRP composite be exteneded over a point of cracking moment. In this study, the failure mode and the flexural performance of RC beam with different bond length of FRP are estimated. Each bonded length is calculated based on the point of cracking moment with addition or subtraction of specific length(=150mm). The results of this study show that mid-span debonding occurs in the specimen strengthened with CFRP strips which are bonded over the point of cracking moment, while concrete cover deliamination occurs at the termination point of CFRP in the specimen with less bonded length than the point of cracking moment region.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.129-132
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• 2006

It is generally reported that most of RC beams strengthened with simply bonded FRP composite is failed by FRP debonding. Also, the flexural performance of RC member strengthened with FRP composite can be calculated using the effective strain of FRP. The effective strain as a result of the debonding failure depends on many variables, such as FRP stiffness including the thickness($t_f$) and modulus of elasticity($E_f$), the amount of FRP but the FRP stiffness is reportedly the most influential. The purpose of this paper, therefore, is to examine effects of FRP stiffness on the flexural strengthening of RC beams. 4 different stiffness of CFRP composite including CFRP sheet and laminae were selected. From the tests, it was found that the flexural performance of RC beams strengthened with CFRP composite can be calculated based on the effective strain of the CFRP composite and the effective strain is inversely proportional to the CFRP stiffness.

• Journal of Ocean Engineering and Technology
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• v.20 no.3 s.70
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• pp.77-81
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• 2006

In this study, design parameters of ice-transiting vessels in the world, currently in service or under construction, were collected and a database of principal particulars for each ship was established. To understand the recent design trend, ice-transiting vessels were categorized into four groups, i.e., conventional icebreakers, icebreaking tug/supply/research vessels, ice-strengthened passenger/car ferry and ice-strengthened cargo vessels. Changes in principal particulars for each group were reviewed and summarized. It was found that the most significant change in the design of ice-transiting vessels was the increment of large size commercial cargo vessels. It is believed that the recent hike of oil prices and booming of Russian economy has resulted in the need for year-round operation with bigger ships in the Baltic Sea and in the Sea of Okhotsk and also along the Northern Sea Route in Russian Arctic Sea.

• Computers and Concrete
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• v.13 no.4
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• pp.517-529
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• 2014

In order to increase the load carrying capacity and/or increase the service life of existing circular reinforced concrete bridge columns, Carbon Fiber Reinforced Polymer (CFRP) composites could be utilized. Transverse wrapping of circular concrete columns with CFRP sheets increases its axial and shear strengths. In addition, it provides good confinement to the concrete column core, which enhances the bending and compressive strength, as well as, ductility. Several experimental and analytical studies have been conducted on CFRP strengthened concrete cylinders/columns. However, there seem to be lack of thorough investigation of the effect of elevated temperatures on the response of CFRP strengthened circular concrete columns. A concrete confinement model that reflects the effects of elevated temperature on the mechanical properties of CFRP composites, and the efficiency of CFRP in strengthened concrete columns is presented. Tensile strength and modulus of CFRP under hot conditions and their effects on the concrete confinement are the primary parameters that were investigated. A modified concrete confinement model is developed and presented.