• Journal of the Korean Geotechnical Society
• /
• v.34 no.4
• /
• pp.13-25
• /
• 2018

When deformation occurs on slope reinforced with anchor, shear stress and bending stress are applied on the shear surface along the slip surface and increase of the shear deformation causes the tension force variation of the anchor. In this study, shear test was performed by measuring the tension force of the anchor by inducing shear deformation in vertical direction of the anchor using a large-scale direct shear test equipment in order to confirm the tension force variation of the anchor induced by shear deformation. The shear test was performed for 8 conditions which were classified according to the anchor reinforcement, separation distance (1D, 2D, 4D) from the shear surface to bonded part and the lateral-pressure condition (0.1 MPa, 0.2 MPa) of adjacent ground. As a result of the shear test, it was found that the separation distance and the lateral-pressure condition affect the shear force of the ground reinforced by anchor and the tension force of the anchor, and experimentally verified that the shear force variation is related to axial force variation of the anchor head and tip. Therefore, it was confirmed that the behavior of the bonded part induced by the shear deformation can be indirectly predicted by analyzing the tendency of the tension force variation of the anchor head.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.6
• /
• pp.137-146
• /
• 2005

299 railroad slopes were investigated and the failure characteristics and reinforcement patterns were analyzed. Stability analyses on the 14 cut-off soil slopes were carried out. Surficial failures were predicted by infinite slope analyses assuming the temporarily perched ground water table at soil surface during rainfall period. Limit equilibrium analyses were also carried out and the influences of rainfall infiltration on the slope stabilities were taken Into account by seepage analyses using finite element method and by assuming ground water tables to be located adjacent to soil surface. The adequacy of those analyses was evaluated by comparing the slope failure characteristics between analysis results and the past failure records. From the comparison results, it was deduced that the limit equilibrium analyses were not appropriate to estimate the shallow failure that occurred at most of the railroad cut-off soil slopes. For the better estimation of the surficial failure, not only the increase of pore-water pressure (reduction of matric suction), but also the influence of water flows over slope surface which erode soil mass, should be evaluated and considered.

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

• Journal of the Korean Society for Railway
• /
• v.18 no.3
• /
• pp.261-269
• /
• 2015

To overcome the weaknesses of viaduct bridges and the non-economic efficiency of underground LRT, the study of near-surface railway systems is in progress. To apply a box structure to the low depth transit, a connection joint to precast modules are very important when applying precast modular structures to replace temporary structures. In this study, wall to wall connections were applied in diverse cases such as rebar connections, guiding structures that were used to fit the verticality of precast walls during construction, and non-reinforcement structures used only for waterstop. Experimental performance verification was carried out for the bending, shear and splitting of the wall to wall connection. Precision of construction joints between wall to wall was identified as a factor that influenced the structural performance of the precast wall. A structure that can serve as a guide during the vertical insertion of a wall is confirmed for the most suitable case, but it will be necessary to modify this structure for detailed cases.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.8
• /
• pp.95-105
• /
• 2005

Generally, a modified version of limit equilibrium method can be used to evaluate a slope stability of the geosynthetic reinforced soil slopes. In most cases, resisting effects of geosynthetic reinforcement are dealt with considering an increased shear strength on the potential slip surface. However, it is not clear that the methods satisfy all three equilibrium equations. As we know, the pattern of normal stress distribution along the slip surface is the key factor in calculating the safety factor of slopes. In this study, the new slope stability analysis method in which not only reinforcing effects of geosynthetics can be considered but also all three equilibrium equations can be satisfied was proposed with assuming the normal stress distribution along the slip surface as quadratic curve with horizontal $\chi-coordinate$. A number of illustrative examples, including published slope stability analysis examples for the reinforced and unreinforced soil slopes, loading test of large scale reinforced earth wall and centrifuge model tests on the geotextile reinforced soil slopes, were analyzed. As a result, it is shown that the newly suggested method yields a relatively accurate factor of safety for the reinforced and unreinforced soil slopes.

• Journal of Adhesion and Interface
• /
• v.13 no.2
• /
• pp.58-63
• /
• 2012

CFRP chip is the byproduct from carbon fiber reinforced plastic (CFRP) processing. CFRP chip is not simply a waste mainly composed of fine carbon fiber and epoxy resin. CFRP chip keeps matrix to maximize their reinforcing effect. To obtain a uniform length of carbon fiber in CFRP chip, chip was chopped ina mortar. CFRP chip should be purified to get better interface adhesion. Epoxy resin on the carbon fiber was removed by $H_2O_2$ surface etching treatment. Optimal dispersion and fabrication conditions of CFRP chip embedded in phenolic resin were determined by thermal stability for fire retardant applications. CFRP chip-phenolic composite exhibits better mechanical and thermal properties than neat phenolic resin. Surface condition of CFRP chip-phenolic composite was evaluated by static contact angle measurement. Contact angle of CFRP chip-phenolic composite was greater than neat phenolic due to heterogeneous condition of fine carbon fibers. From the evaluation for fire retardant (ASTM D635-06) test, thermal stability of CFRP chip-phenolic composite was found to be improved with higher concentration of CFRP chip.

• Journal of Conservation Science
• /
• v.37 no.5
• /
• pp.536-544
• /
• 2021

In the present study, safe management and value improvement of bamboo sunblind, which is an item of cultural heritage, were performed by adopting stable conservation treatment methods. The bamboo sunblind used in the present study was excavated from No. 1 catchment site in Baesanseongji, Busan. It was determined that the main material used to make the sunblind was bamboo, and herbal plants were used to weave the bamboo using lacquer as an adhesive agent. All contaminants and soil adhered to the sunblind was removed. Thereafter, the sunblind, which was recovered in the form of blocks, was washed separately after fixing it to a temporary plaster frame and to avoid the blocks from breaking during washing. Then, polyethylene glycol (PEG) impregnation was utilized for the reinforcement treatment. Based on the preliminary test results, the shape of the sunblind was fixed using a stainless-steel frame to prevent physical damage that may occur during the drying process. Thereafter, the bamboo sunblind was vacuum freeze-dried. PEG 20% (in ethyl alcohol) was applied as a surface treatment agent for stabilization the sunblind. After the surface treatment, the bamboo sunblind were joined together to fit the maximum width, and the rectangular shape of the sunblind was restored-as best as possible-while filling in the missing parts by maximizing the use of unknown members such as in the disturbed layers below bamboo sunblind surface. The conservation treatment was completed by fixing the bamboo sunblind into the fabricated frame.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.28 no.4
• /
• pp.121-132
• /
• 2023

Marine heatwaves (MHWs), referring to anomalously high sea surface temperatures, have drawn significant attention from marine scientists due to their broad impacts on the surface marine ecosystem, fisheries, weather patterns, and various human activities. In this study, we examined the impact of the distribution of Changjiang diluted water (CDW), a significant factor causing oceanic property changes in the East China Sea (ECS) during the summer, on MHWs. The surface salinity distribution in the ECS indicates that from June to August, the eastern extension of the CDW influences areas as far as Jeju Island and the Korea Strait. In September, however, the CDW tends to reside in the Changjiang estuary. Through the Empirical Orthogonal Function analysis of the cumulative intensity of MHWs during the summer, we extracted the loading vector of the first mode and its principal component time series to conduct a correlation analysis with the distribution of the CDW. The results revealed a strong negative spatial correlation between areas of the CDW and regions with high cumulative intensity of MHWs, indicating that the reinforcement of stratification due to low-salinity water can increase the intensity and duration of MHWs. This study suggests that the CDW may still influence the spatial distribution of MHWs in the region, highlighting the importance of oceanic environmental factors in the occurrence of MHWs in the waters surrounding the Korean Peninsula.

• Journal of the Korean GEO-environmental Society
• /
• v.25 no.8
• /
• pp.13-19
• /
• 2024

In this study, to reinforce the surface layer of weathered soil slopes where erosion and collapse of surface layer occur, compression strength tests were conducted by mixing carbon fiber and eco-friendly stabilizer (E.S.B.) To determine the optimal mixing ratio of E.S.B. and carbon fiber, E.S.B. was set at conditions of 10%, 20%, and 30%, and carbon fiber at 0.3%, 0.6%, 0.9%, and 1.2%. Additionally, to analyze the changes in compressive strength according to dry density and curing period, 85% and 95% of the maximum dry unit weight were applied, and curing periods were set to 3 days, 7 days, and 28 days. The standard strength for surface layer reinforcement of slopes is proposed as 4 MPa at 7 days and 6 MPa at 28 days according to ACI 230.1R-09 (2009). The compression test results showed that the unconfined compressive strength of E.S.B. reinforced soil met the standard strength at an E.S.B. mixing ratio of 10% or more for 95% compaction. Moreover, when carbon fiber was mixed with E.S.B. reinforced soil, a ductile fracture pattern was observed after the yield point due to compressive strength, indicating that the mixture could compensate for post-yield failure. It was analyzed that the maximum strength is exhibited at a carbon fiber mixing ratio of 0.6%. The unconfined compressive strength of carbon fiber reinforced soil increases by approximately 54-70% compared to the condition without carbon fiber.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.18 no.3
• /
• pp.145-155
• /
• 2002

The results of the present feasibility study are summarized as follows, 1. The three unit bridge of knitted material and UD fibre reinforcement has both the rigidity and the strength against a vertical occlusal load of 75N. 2. Stress concentration at the junctional area between the bridge and the abutments, i.e. between the pontic and the knitted caps was observed. In the case of the bridge with reinforcement straps, it was partly shown that the concentration problem could be improved by simply increasing the fillet size at the area. Further refining in the surface of the junctional area will be needed to ensure a further improvement in the stress distribution. This will require some trade off in the level of the stress and the available space. A parametric study will help to decide the appropriate size of the fillet. 3. Design refinement is a must to improve the stress distribution and realize the most favourable shape in terms of fabrication. The current straight bar with a constant cross section area can be redesigned to a tapered shape. The curve from the dental arch should also be placed on the pontic design. In accordance with design refinement, the resistance of the bridge frame to other load cases should be evaluated. 4. Although not included in the present feasibility study, it is estimated that bridges of the anterior teeth can be made strong enough with the knitted material without further reinforcement using unidirectional materials. In this regard, a feasibility study on design concepts and stress analysis for 3, 4, 5 unit bridge is suggested. 5. Two types of bridge were analysed in terms of fatigue. The safe life design concept, i.e. fatigue design concept, looks reasonable for the bridge where if cracks should form and propagate there is virtually nothing a dentist to do. The bridge must be designed so that no crack will be initiated during the life span. In the case of crowns, however, if constructed with composite resin with knitted materials, it might be possible to repair them, which in general is impossible for crowns of PFM or of metal. Therefore for composite resin crowns, a damage tolerance design concept can be applied and reasonably higher operational stresses can be allowed. In this case, of course, a periodic inspection program should be established in parallel. 6. Parts of future works in terms of structural viewpoint which need to be addressed are summarized as the following: 1) To develop processing technology to accommodate design concepts; 2) More realistic modelling of the bridge and analysis-geometry and loading condition. Thickness variation in the knitted material, taper in the pontic, design for anterior tooth bridge, the effect of combined loads, etc, will need to be included; 3) To develop appropriate design concepts and design goals for the fibre composite FPD aiming at taking the best advantage of knitted materials, including the damage tolerance design concept; 4) To develop testing method and perform test such as static ultimate load test, fatigue test, repair test, etc, as necessary.