• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.193-202
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• 2008

This paper investigates experimentally the confining effect, strengthening capacity and rebound rate of sprayed Fiber-Reinforced-Polymer (SFRP). From the method, resin and chopped fibers are sprayed separately from the nozzle with high pressure, and then they are attached to the concrete surface, so structure could be repaired. To evaluate the strengthening effect of sprayed FRP, cylindrical specimens and beam specimens were strengthening with SFRP. As main material of FRP, glass fiber and polyester resin are used. To investigate the optimum condition of sprayed FRP, the effects of fiber length, coating thickness, fiber volume ratio and concrete strength were examined. Capacities of sprayed FRP method were also compared to the FRP sheet method. In case of the sprayed FRP, rebound rate is important parameter considering economical efficiency and constructibility, so rebound rate of was discussed. From the test results, optimum conditions of sprayed FRP were determined. SFRP method showed superior strengthening capacities than FRP sheet method.

• Journal of The Korean Society of Integrative Medicine
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• v.5 no.2
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• pp.19-23
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• 2017

Purpose: The purpose of this study was to determine the muscle activity ratio according to the shoulder abduction angle by identifying the mean muscle activities and calculating the muscle ratios for use in developing strengthening methods. Methods: The participants were healthy adults in their 20s (n=19). The activity of the deltoid middle, upper trapezius, middle trapezius, and lower trapezius muscles was measured by 8-channel surface electromyography. Muscle activity was measured during 4 conditions of angle of shoulder abduction: $30^{\circ}$, $60^{\circ}$, $90^{\circ}$, and $120^{\circ}$. The data used in the analysis were the root mean square and % total muscle activity values. Results: The root mean square values for the deltoid middle, upper trapezius, middle trapezius, and lower trapezius muscles showed significant differences. No significant differences were detected in the % total muscle activity of the deltoid middle, upper trapezius, middle trapezius, or lower trapezius muscles. Conclusion: Future studies aimed at developing selective shoulder abductor muscle strengthening methods are likely to provide more effective results by using muscle activity ratios.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.148-153
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• 2018

In this study, the nonlinear time history analysis of seismic retrofitted structures with TS damper for seven ground motion records was conducted for the purpose of verifying the seismic strengthening effect of TS seismic retrofitting method. Through comparison of the interstory drift ratio and the energy dissipation amount of the non - reinforced structure obtained and those of retrofitted structures with TS damper from the nonlinear time history analysis, the interstory drift ratio was reduced by about 30% and the amount of energy dissipation through the structure was halved. As a result, it was confirmed that the damping performance of the TS seismic retrofitting method is excellent.

• Journal of Korean Physical Therapy Science
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• v.10 no.1
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• pp.74-82
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• 2003

The purpose of this study is to provide guideline of muscle strengthening exercise for preparing ambulation by presenting suitable ratio of muscle power of agonist & antagonist, and that of concentric & eccentric contraction on behalf of amputee's normal ambulation training and it's strenthening as well. 7 Subjects who have femur amputee for experimental group were able to ambulate naturally without inconvenience and 20 adult subjects of comparison group for comparison were considered to be free from disturbance of ambulation. The method of study was to measure the muscle power of hip pint, was to figure out the ratio of agonist & antagonist, concentric contraction & eccentric contraction, and was to find out mean and standard deviation of each measurement. Every numerical value of comparison was tested by Mann-whitney and comparison group's comparison between left & right value was done with t-test. Results are as followings : 1) Extension force was stronger than flexor force and had no remarkable difference(p<0.05) 2) For normal adults, adduction farce was stronger than abduction force and for amputees, abduction force was stronger while adduction force was the same as the normal without showing remarkable difference(p<0.05) According the result above, I make an assumption that maintaining a proper ratio of muscle power on strengthening exercise for amputee's ambulation training & rehabilitation and finally bring out an improvement of transfer and ambulation.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.421-431
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• 2007

The main purpose of this study is to develop a sprayed FRP repair and strengthening method, which is a new technique for strengthening the existing concrete structures by mixing one of the carbon or glass chopped fibers and one of the epoxy or vinyl ester resins with high-speed compressed air in open air and randomly spraying the mixture onto the concrete surface. At present, the sprayed FRP repair and strengthening method using the epoxy resin has not been fully discussed. In order to investigate the material property of the sprayed FRP, this study carried out tensile tests of the material specimens, which were changed with the combinations of various variables including the length of chopped fiber and the mixture ratio of chopped fiber and resin. These variables were set to have the equal material strength, compared with that of one layer of the FRP sheet. As a result, the optimal length of glass and carbon chopped fibers was fumed out to be 38 mm, and the optimal mixture ratio between chopped fiber and resin was also turned out to be 1 : 2 from each variable. And also, the thickness of the sprayed FRP to have the equal strength to one layer of the FRP sheet was finally calculated. In is study, a series of experiments were carried out to evaluate the strengthening effects of flexural beams, shear beams and damaged beams strengthened with the sprayed FRP method, respectively. The results revealed that the strengthening effects of the flexural and shear specimens were reasonably similar to those of the FRP sheet, and the developed Sprayed FRP technique is able to be used as a strengthening scheme of existing RC building.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.4
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• pp.73-78
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• 2004

The conventional SLT(Shear Lag Theory) which has been proven that it can not provide sufficiently accurate strengthening predictions in elastic regime when the fiber aspect ratio is small. This paper is an extented work to improve it by modifying the load transfer mechanism called NSLT(New Shear Lag Theory), which takes into account the stress transfer across the fiber ends and the SCF(Stress Concentration Factor) that exists in the matrix regions near the fiber ends. The key point of the model development is to determine the major controlling factor among the material and geometrical coefficients. It is found that the most affecting factor is the fiber/matrix elastic modulus ratio. It is also found that the proposed model gives a good result that has the capability to correctly predict the elastic properties such as interfacial shear stresses and local stress variations in the small fiber aspect ratio regime.

• Earthquakes and Structures
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• v.8 no.3
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• pp.761-778
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• 2015

The objective of this paper is to report the result of an experimental program conducted on the strengthening of nonductile RC frames by using external mesh reinforcement and plaster application. The main objective was to test an alternative strengthening technique for reinforced concrete buildings, which could be applied with minimum disturbance to the occupants. Generic specimen is two floors and one bay RC frame in 1/2 scales. The basic aim of tested strengthening techniques is to upgrade strength, ductility and stiffness of the member and/or the structural system. Six specimens, two of which were reference specimens and the remaining four of which had deficient steel detailing and poor concrete quality were strengthened and tested in an experimental program under cyclic loading. The parameters of the experimental study are mesh reinforcement ratio and plaster thickness of the infilled wall. The effects of the mesh reinforced plaster application for strengthening on behavior, strength, stiffness, failure mode and ductility of the specimens were investigated. Premature and unexpected failure mode has been observed at first and second specimens failed due to inadequate plaster thickness. Also third strengthened specimen failed due to inadequate lap splice of the external mesh reinforcement. The last modified specimen behaved satisfactorily with higher ultimate load carrying capacity. Externally reinforced infill wall composites improve seismic behavior by increasing lateral strength, lateral stiffness, and energy dissipation capacity of reinforced concrete buildings, and limit both structural and nonstructural damages caused by earthquakes.

• KCI Concrete Journal
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• v.14 no.1
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• pp.51-60
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• 2002

Strengthening of existing concrete structures is a major concern in recent years as the number of degraded structures increases. The purpose of this paper is to investigate the static and fatigue behavior of reinforced concrete (RC) beams strengthened with steel plates. To this end, a comprehensive test program has been set up and many series of strengthened beams have been tested. The major test variables include the plate thickness, adhesive thickness, and the shear-span to depth ratio. The test results indicate that the separation of plates is the dominant failure mechanism even for the full-span-length strengthened beams with steel plate. The theoretical ultimate load capacities for strengthened beams based on the full composite action of concrete beam and steel plate are found to be larger than the actual measured load capacities. The strengthened beams exhibit more dominant shear cracking as the shear-span to depth ratio decreases. The ultimate capacity of strengthened beams increases slightly with the increase of adhesive thickness, which may be caused by the late initiation of plate separation in the beams with thicker adhesive. A realistic concept of ductility for plate-strengthened beams is proposed in this study. It is seen that the strengthened beams show relatively low ductility compared with unstrengthened beams. The present study indicates that the strengthened beams exhibit much higher fatigue resistance than the unstrengthened beams. The increase of deflections of strengthened beams according to the number of load cycles is much smaller than that of unstrengthened beams. The present study provides very useful results for the realistic application of plate-strengthening method in reinforced concrete structures.

• Steel and Composite Structures
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• v.43 no.6
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• pp.735-757
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• 2022

The behavior of shear deficient under-balanced reinforced concrete beams with rectangular cross-sections, which were externally strengthened with CFRP composite along shear spans, was experimentally investigated under vertical load. One of the specimens represents a reference beam without CFRP strengthening and the other specimens have different width/strip spacing ratios (w_f/s_f). The optimum strip in terms of w_f/s_f, which will bring the beam behavior to the ideal level in terms of strength and ductility, was determined according to the regulations. When the w_f/s_f ratio exceeds 0.55, the behavior of the beam shifted from shear failure to bending failure. However, it has been observed that the w_f/s_f ratio should be increased up to 0.82 in order for the beam to reach sufficient shear reserve value according to the codes. It is also observed that the direction and weight of the CFRP composite are one of the most critical factors and 240 gr/m² CFRP strips experienced sudden ruptures in the shear span after the cracking of the concrete. It is considered as a deficiency that the empirical shear capacity formulas given for the beams reinforced with CFRP in the regulations do not take into account both direction and weight of CFRP composites.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.235-242
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• 2019

The objective of this study is to modify the mixture proportions of concrete that were developed for section enlargement strengthening elements using a specially designed binder composed of 5% ultra-rapid hardening cement, 10% polymer, and 85% ordinary portland cement in order to assign the self-compaction property to such concrete. The self-compaction abilities of concrete were estimated by the performance criteria specified in JSCE and EFNARC provions. Test results showed that the increase in the unit binder content at the consistent water-to-bider ratio led to increase in viscosity of fresh concrete but did not exhibit the decrease in the fluidity due to a greater viscosity. The mixture proportioning of self-compaction section enlargement concrete could be considered at the following conditions: unit binder contents of $430kg/m^3{\sim}470kg/m^3$ and fine aggregate-to-total aggregate ratios of 40%~46% at the water-to-binder ratio of 38%.