• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.102-112
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• 2012

Recently, the near surface mounted (NSM) FRP strengthening technique has been actively applied to deteriorated concrete structures for rehabilitation purposes. However, the use of this conventional NSM technique could be restricted due to the insufficient height or strength of the concrete cover. In this study, the stirrup-Cutting Near Surface Mounted(CNSM) technique was considered as an alternative, whereby NSM strips are placed at a deeper level, namely at the level of the main steel reinforcement. A flexural test of a concrete beam strengthened with CNSM technique was performed and the results were then compared to those for a concrete beam strengthened by the conventional NSM technique. The embedment length of the CFRP strips was varied in order to increase the effect of the anchoring depth of the NSM and CNSM CFRP strips in the beam specimens. From the results of the test, the beam with the CNSM CFRP strip showed typical structural behavior similar to that of the beam with the NSM CFRP strip. Moreover, there was no apparent structural degradation resulting from the stirrup partial-cutting. Consequently, the CNSM strengthening technique can be suitably utilized for extensively damaged concrete structures where it is difficult to apply the conventional NSM technique.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.4
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• pp.75-83
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• 2013

This paper presents a series of test result in order to study fire resistance capacity of the Near-Surface-Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) plate, which are tensile test of CFRP under various temperature loading, temperature loading test of epoxy and bond test of NSM CFRP to concrete under various temperature loading. From the tests, it was found that NSM retrofit method had high efficiency in strengthening concrete under ordinary temperature. However, the strength of the system was able to be drastically decreased even a little increase of surrounding temperature. Especially, bond capacity begins to disappear when the surrounding temperature approaches the glass transition temperature of epoxy. Therefore, it is necessary to improve the fire resistance capacity of both fiber reinforced polymer reinforcement and epoxy for bonding in order to develop safe fire resistance design of structure.

• Advances in concrete construction
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• v.16 no.4
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• pp.205-216
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• 2023

Concrete structures may become vulnerable during their lifetime due to several reasons such as degradation of their material properties; design or construction errors; and environmental damage due to earthquake. These structures should be repaired or strengthened to ensure proper performance for the current service load demands. Several methods have been investigated and applied for the strengthening of reinforced concrete (RC) structures using various materials. Fiber reinforced polymer (FRP) reinforcement is one of the most recent type of material for the strengthening purpose of RC structures. The main objective of the present research is to identify the behavior of reinforced concrete slabs strengthened with FRP bars by using near surface mounted (NSM) technique. Validation study is conducted based on the experimental test available in the literature to investigate the accuracy of finite element models using LS-DYNA to present the behavior of the models. A parametric analysis is conducted on the effect of FRP bar diameters, number of grooves, groove intervals as well as width and height of the grooves on the flexural behavior of strengthened reinforced slabs. Performance of strengthening RC slabs with NSM FRP bars was confirmed by comparing the results of strengthening reinforced slabs with control slab. The numerical results of mid-span deflection and stress time histories were reported. According to the numerical analysis results, the model with three grooves, FRP bar diameter of 10 mm and grooves distances of 100 mm is the most ideal and desirable model in this research. The results demonstrated that strengthening of reinforced concrete slabs using FRP by NSM method will have a significant effect on the performance of the slabs.

• Journal of the Korean Society of Safety
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• v.24 no.3
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• pp.39-46
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• 2009

A recent and promising method for shear strengthening of reinforced concrete(RC) members is the use of near surface mounted(NSM) fiber reinforced polymer(FRP) reinforcement. In the NSM method, the reinforcement is embedded in grooves cut onto the surface of the member to be strengthened and filled with an appropriate binding agent such as epoxy paste or cement grout. This paper illustrates a research program on shear strengthening of RC beams with NSM channel-type FRP beams which is developed in this study. The objective of this study is to clarify the role of channel-type FRP beam embedded to the beam web for shear strengthening of reinforced concrete beams. Included in the study are effectiveness in terms of spacing and angle of channel-type FRP beams, strengthening method, and shear span ratio. the study also aims to understand the additional shear capacity due to glass fiber reinforced polymer beams and carbon reinforced polymer beams. And anther objective is to study the failure modes, shear strengthening effect on ultimate force and load deflection behavior of RC beams embedded with channel-type FRP beams on the shear region of the beams.

• Smart Structures and Systems
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• v.1 no.4
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• pp.385-404
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• 2005

The paper presents a model to calculate reinforcement strain using measured crack width in members under applied tension, flexure, and/or shear stress. Crack mapping using a new type of distributed coaxial cable sensors for health monitoring of large-scale civil engineering infrastructure was recently proposed and developed by the authors. This paper shows the results and performance of such sensors mounted on near surface of two flexural beams and a large scale reinforced concrete box girder that was subjected to cyclic combined shear and torsion. The main objectives of this health monitoring study was to correlate the sensor's response to strain in the member, and show that magnitude of the signal's reflection coefficient is related to increases in applied load, repeated cycles, cracking, and reinforcement yielding. The effect of multiple adjacent cracks, and signal loss was also investigated. The results shown in this paper are an important step in using the sensors for crack mapping and determining reinforcement strain for in-situ structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.131-136
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• 2013

The purpose of this study is to establish the flexural strengthening method of the concrete members. To accomplish this objective, a total of seven concrete beams were tested. From this study, it is found that the initial flexural stiffness and strength of the beams reinforced with NSM CFRP strips were significantly improved compared to the beam without CFRP strip. Failure of the beam reinforced with NSM strips is initiated by failure of NSM strips, eventually sudden explosive compressive failure in the loaded region. This strengthening method combined with NSM CFRP strips and high performance mortar for concrete cover recovery is evaluated by a good strengthening method for the strength, durability and good appearance of concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.5
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• pp.178-189
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• 2011

Tests and analyses were performed in this study to assess the shear strength of Reinforced Concrete(RC) members strengthened by the Near Surface Mounted(NSM) technique in shear, which is drawing attention as an alternative to the Carbon Fiber Reinforced Polymer(CFRP) bonding strengthening technique. Four-point bending tests were performed on 7 RC specimens without any shear reinforcement. The test variables such as the inclination of CFRP strip (45 degrees and 90 degrees), and the spacing of CFRP strip (250mm, 200mm, 150mm, 100mm) were considered. Through the testing scenarios, the effect of each test variable on the failure mode and the shear strength of the RC members strengthened by the NSM technique in shear were assessed. The test results show that the specimens with CFRP strips at 45 degrees go to failure as a result of the strip fracture, but the specimens with CFRP strips at 90 degrees go to failure as a result of the slip of strips. Strips at 45 degrees was the more effective than strips at 90 degrees, not only in terms of increasing beam shear resistance but also in assuring larger deformation capacity at beam failure. In addition, the RBSN analysis appropriately predicted the crack formation and the load-displacement response of the RC members strengthened by the NSM technique in shear.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.195-198
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• 2005

To investigate the strengthening efficiency of the Near Surface Mounted Reinforcement (NSMR) technique analytically, a structural model for the finite element method (FEM) able to simulate accurately the experimental results was determined. Applying the finite element model, parametric analysis was performed considering the groove depth and spacing of CFRP laminates. Analytical study on the groove depth revealed the existence of a critical depth beyond which the increase of the ultimate load becomes imperceptible. Analytical results regard to the spacing of the CFRP laminates showed that comparatively smooth fluctuations of the ultimate load were produced by the variation of the spacing and the presence of an optimal spacing range for which relatively better strengthening efficiency can be obtained. Particularly, a spacing preventing the interference between adjacent CFRP laminates and the influence of the concrete cover at the edges as well as allowing the CFRP laminatesto behave independently was derived.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.473-476
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• 2004

Carbon Fiber Reinforced Polymer(CFRP) composites are widely applied to strengthen deteriorated concrete structures. This paper presents the experimental results of the performance of reinforced concrete(RC) beams strengthened with Near Surface Mounted T-shape CFRP. Simple beams with 3m span length were tested to investigate the effect of CFRP reinforcement shapes on the flexural behavior of strengthened RC beams. The test results were analyzed with the special emphasis on the failure mode and the maximum load.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.153-156
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• 2006

This paper presents an analytical results on limits of debonding failure for RC beams strengthened with near-surface mounted(NSM) CFRP strips. An analytical model was derived to predict the failure mode and the maximum load. An analytical model has two assumptions. The first is that the debonding failure occurs at the epoxy-concrete interfaces. The second is that the debonding failure occurs at the end of the FRP reinforcement due to concentration of shear stress. Results of the comparison of existing test data and analytical model data have predicted the failure mode and the maximum load well. Also, this paper proposed limits of debonding failure to prevent the debonding using the strengthening area and the groove depth.