• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.4 s.56
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• pp.126-136
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• 2009

The sprayed FRP strengthening technique is combining the Glass fiber and Polyester resin in open air and spraying randomly at concrete's surface with high-speed compressed air. Then it strengthens the structures with a new technique evaluated the structural performance. We applied it to concrete beam and tested for flexural strength, depended on Korea Standard(KS F 2408). Then based on the result of flexural strength, the properties were proposed that applying to structures. Based on the experiment, we have evaluated structural performance by the experiment. 1/5 scale prestressed concrete I-beam were made by Korean Highway's typical drawing in 1993. With these test results, 49.8% increased in flexural strength, improvement of the behavior of serviceability state, and strengthening was surely effective for controlling deflection and crack of structure. Consequently, it can be summarized that Sprayed FRP technique has prospect to improve the performance of structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.2
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• pp.103-112
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• 2008

Pull-off test is generally used to evaluate bond strength of FRP composite with concrete at job site. However, some damages on FRP composites can not be avoided during pull-off test and moreover test range of pull-off strength is limited by maximum tensile strength of concrete. Accordingly, it is required to set-up a test method that can evaluate mechanical properties of structural adhesive indirectly prior to pull-off test. In this study, the standard test methods for structural adhesive which can simply evaluate mechanical performance of adhesive were suggested through comparative experiments from each different standard in various countries. Particularly, gluing thickness of adhesive in tensile lap-shear tests, the section dimension of compression and bending test specimens become unified, and standard test specimen size is achieved by test results.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.134-142
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• 2020

In this study, in order to evaluate the self-healing performance of cement composites the self-healing test method and the analysis method were suggested by applying constant water head permeability test, chloride migration test and repeated bending test. The method of making a cracked specimen and controlling crack width are also proposed. Constant head water permeability test can evaluate the healing performance by using the decreasing rate of water flow passing through the crack zone of a specimen. Furthermore, the equivalent crack width can be used to intuitively investigate the healing effect with healing period. The chloride migration test can evaluate the healing rate by the decreasing rate of the diffusion coefficient obtained by ASTM C 1202. Mechanical healing performance can be evaluated using ISR and IDR estimated from load vs. CMOD relationship graph obtained through the repeated bending test. Finally, the applicability of proposed self-healing evaluation methods was examined by testing mortar specimens with or without self-healing agents.

• Journal of the Korean Society of Radiology
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• v.7 no.5
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• pp.313-320
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• 2013

For some patients with joint illnesses such as rheumarthritis or varus deformity, the total knee arthroplasty (TKA) procedures are performed. However, when inserting metal cutting guide for the procedures, due to the femoral shaft bowing, complications such as the cortex of the femoral shaft damages or secondary fractures can be caused. If the central coordinate value of the femoral shaft is known, the metal cutting guide could be inserted into the anatomical center, so such complications can be prevented. In this study, CT images of femoral shafts of 10 individuals in the experiment group who are in need of receiving the total knee arthroplasty procedures and those of 10 individuals in the control group without illness in the femoral shaft have been utilized to locate the 3-dimensional coordinate values. Then, Matlab was utilized to identify the central coordinate value in order to obtain a graph reflecting the anatomical shapes as well as to acquire the 3-dimensional radial curvature values by section. As a result, the average curvature range and standard deviation of femoral shafts of the experiment group was determined to be $758.15{\pm}206.3mm$ whereas the that of the control group was determined to be $1672.97{\pm}395.6mm$. The statistical significance of the measured results was verified through f-distribution analysis. Based on these results, it was verified that the level of curvature of the femoral shaft of the experiment group was higher. If the anatomical central points are located and analyzed using this methodology, it would be helpful in performing orthopedic operations such as the total knee arthroplasty.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.216-222
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• 2002

With deterioration of the nation's infrastructure comes the growing, need for effective means of rehabilitating structures. Possibly one for the most challenging tasks is to upgrade the overall capacity of concrete structure. Therefore, considerable efforts are still being made to develop new construction materials. Rehabilitation of damaged RC structures occasionally requires the removal and replacement of concrete in the tension zone of the structural members. Typical situation where the tension zone repair is necessary is when the concrete in the tension zone in beams or slabs has spalled off as a result of corrosion in the bottom reinforcing bars or due to extensive fire. The rehabilitation of such conditions normally involves the removal of the concrete beyond the reinforcement bars, cleaning or replacing the tensile bars and reinstatement of concrete to cover the steel bars the original shape and size. This study focused on the flexural behavior of reinforced concrete beams strengthened by steel strand and carbon fiber sheet in the tension zone. The properties of beams are 15$\times$25 cm rectangular and over a 200cm span. Test parameters in this experimental study were strengthening methods, jacking volume, the number of sheet. We investigated the flexural behavior of simply supported RC beams which are strengthened with the carbon fiber sheet, monotonic loads. Attention is concentrated upon overall bending capacity, deflection, ductility index, failure mode and crack development of repaired and rehabilitated beams.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.48-54
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• 2020

Cracks in reinforced concrete structures are the most common type of damage and are used as important analytical data to understand the fracture behavior characteristics of structures. Currently, there is a problem that most of the crack investigation relies on visual inspection, therefore many researchers have proposed image analysis techniques to improve the problem. In this study, we proposed a crack evaluation method to be applied at an indoor experimental level using image analysis method. The image analysis technique using color is for distinguishing a boundary surface between objects existing in an image, and is a method for separating similar colors into one region based on a predefined color. In this study, to improve the accuracy of image analysis, blue paint was applied to the concrete surface and bending experiments were performed. The image analysis method was able to measure the crack width with superior accuracy compared to the crack diameter, and at the same time, it was also possible to analyze the deflection of the beam. Both the crack and deformation were able to confirm the accuracy similar to the existing measurement method, and it was found that the image analysis method was very excellent in terms of applicability.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.109-120
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• 2011

This paper presents an experimental study results on the crack control of flexure-dominant reinforced concrete beams repaired with strain-hardening cement composite (SHCC). Five RC beams were fabricated and tested until failure. One unrepaired RC beam was a control specimen (CBN) and remaining four speciemens were repaired with SHCC materials. The test parameters included two types of SHCC matrix ductility and two types of repair method (patching and layering). Test results demonstrated that RC beams repaired with SHCC showed no concrete crushing or spalling until final failure, but numerous hair cracks were observed. The control specimen CBN failed due to crushing. It is important to note that SHCC matrix can improve crack-damage mitigation and flexural behavior of RC beams such as flexural strength, post peak ductility, and energy dissipation capacity. In the perspective of crack width, crack widths in RC beams repaired with SHCC had far smaller crack width than the control specimen CBN under the same deflection. Especially, the specimens repaired with SHCC of PVA0.75%+PE0.75% showed a high durability and ductility. The crack width indicates the residual capacity of the beam since SHCC matrix can delay residual capacity degradation of the RC beams.

• Journal of the Korean Wood Science and Technology
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• v.40 no.1
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• pp.26-37
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• 2012

Recently, the demand and supply on the Hanok have been increased. However, Hanok should be requested larger section of structural members because of excessive roof weight. So, structural skin-timber was manufactured to get a lightweight structural member. The structural skin-timber has exterior shape with larger section but a great volume of wood be removed. The reduced strength of structural skin-timber can be supplemented by hybridizaion of structural member. Japanese larch and Domestic pine were used to manufacture the structural skin-timber. Structural skin-timbers of rectangular shape and cylinder shape were manufactured and tested to evaluate the bending properties. The intended strength property could not be obtained because member had been suffered severe damage by precision deficiency of manufacturing machine. However, if precision of manufacturing machine would be improved and additional hybridizaion of structural skin-timber would be done, lightweight structural member will be able to be manufactured. Structural skin-timber did not showed statistical significancy between two species, so it is possible to use pine mixed with larch. Only MOR of larch showed statistical significancy between rectangular shape and cylinder shape, so it is necessary to use of those as separate things. However, the rest of skin-timber can be judged mixed using because of non statistical significancy. The objective of this study was the development of lightweight larger structural member with relatively strength. If hybrid member of skin-timber could be developed with wood-ceramics, lightweight steel and more, it can be possible to be used as a building material of Hanok, interior material, post & beam construction material and more.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.73-82
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• 2022

The study presents a three-dimensional approach to simulate the nonlinear behavior of a 72 m long Ultra High Performance Fiber Reinforced Concrete (UHPFRC) pre-stressed box girder for a pedestrian bridge in Busan, South Korea. The concrete damage plasticity (CDP) model is adopted to model the non-linear behavior of the UHPFRC material, in which the material properties are obtained from uniaxial compressive and tensile tests. The simulation model based on the proposed stress-strain curve is validated by the results of four-point bending model tests of a 50 m UHPFRC pre-stressed box girder. The results from the simulation models agree with the experimental observations and predict the flexural behavior of the 50 m UHPFRC pre-stressed box girder accurately. Afterward, the validated model is utilized to investigate the flexural behavior of the 72 m UHPFRC pre-stressed box girder. Here, the load-deflection curve, stress status of the girder at various load levels, and connection details is analyzed. The load-deflection curve is also compared with design load to demonstrate the great benefit of the slender UHPFRC box girder. The obtained results demonstrate the applicability of the nonlinear finite element method as an appropriate option to analyze the flexural behavior of pre-stressed long-span girders.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.47-60
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• 2023

At present, in South Korea, there is a growing concern regarding solar power facilities installed on slopes because they are prone to damage caused by natural disasters, such as heavy rainfall and typhoons. Each year, these solar power facilities experience soil erosion due to heavy rainfall and foundation damage or detachment caused by strong wind loads. Despite these challenges, the interaction between the ground and structures is not adequately considered. Current analyses primarily focus on the structural stability under external loads; the overall facility site's stability-excluding the solar structures-in relation to its surrounding slopes is neglected. Therefore, in this study, we use finite-difference method analysis to simulate the behavior of the foundation and piles to assess changes in lateral displacement and bending stress in piles, as well as the safety factor of sloped terrains, in response to various influencing factors, such as pile diameter, spacing between piles, pile-embedding depth, wind loads, and dry and wet conditions. The analysis results indicate that pile spacing and wind loads significantly influence lateral displacement and bending stress in piles, whereas pile-embedding depth strongly influences the safety factor of sloped terrains. Moreover, we found that under certain conditions, the design criteria in domestic standards may not be met.