• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.51-52
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• 2010

The effect of bond strength of longitudinal reinforcing bars on shear strength of reinforced concrete beams is investigated from the view point of arch and truss actions. Stress fields with bond allow us identify possible failure modes including bond failure of a deep beam as well as a slender beam. The slope angle of diagonal compression fields is interpreted as balanced failures of two components involved for shear transfer.

• Tunnel and Underground Space
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• v.30 no.3
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• pp.214-225
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• 2020

Uniaxial compressive strength (UCS) of rock is one of the important factors to determine the advance speed during shield TBM tunnel excavation. UCS can be obtained through the Geotechnical Data Report (GDR), and it is difficult to measure UCS for all tunneling alignment. Therefore, the purpose of this study is to predict UCS by utilizing TBM machine driving data and machine learning technique. Several machine learning techniques were compared to predict UCS, and it was confirmed the stacking model has the most successful prediction performance. TBM machine data and UCS used in the analysis were obtained from the excavation of rock strata with slurry shield TBMs. The data were divided into 8:2 for training and test and pre-processed including feature selection, scaling, and outlier removal. After completing the hyper-parameter tuning, the stacking model was evaluated with the root-mean-square error (RMSE) and the determination coefficient (R²), and it was found to be 5.556 and 0.943, respectively. Based on the results, the sacking models are considered useful in predicting rock strength with TBM excavation data.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.4
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• pp.791-799
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• 1996

The purpose of this study was to compare the shear bond strength of adhesion bridge by various resin cements. One hundred and foully 1st premolars were used. The teeth were cut below 2mm from CEJ and the coronal portions were used. The coronal portions were embeded with the acrylic resin and trimmed with sic paper until the flat plane with ${\phi}$ 4mm above acrylic resin sticks in height 5mm were casted with nonprecious metal and the using surfaces were treated with sic paper from #200 to #1200 and polished with alminum oxide paste. And then, the using surfaces were sandblasted and treated with the electrochemical etching. The teeth were divided into three groups of fourty two each. In group I, teeth and specimens were cemented with Panavia 21 In group II, teeth and specimens were cemented with Superbond In group I, teeth and specimens were cemented with All-Bond & composite resin cement Each group was subdivided into three subgroups according to the storage period ; one-day storage, fifteen-day storage, and thirty-day storage. The special jig was made. Then, the specimen and jig were mounted to Instron Universal Testing Machine and the failure were measured. The results were as follows. 1. There was statisfically significant difference between the failure loads of group I and group II and III after one day storage(P<0.01), 2. There was statisfically significant difference between the failure loads of group II and group I and III and between group I and group III at fifteen day storage(P<0.01). 3. There was statisfically significant difference between the failure loads of group I and II and group III after thirty day storage(P<0.01). 4. There was statisfically significant difference between the failure loads of one day storage and fifteen and thirty days storages in group III (P<0.01).

• Korean Journal of Materials Research
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• v.2 no.6
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• pp.452-460
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• 1992

Effects of the microalloyed elements, temperatures and cooling rates on the strength and toughness of the medium carbon microalloyed hot forging steels obtained by air cooling(A.C.) method and the low carbon microalloyed forging steels by direct quenching(D.Q.) method were investigated. Combined additions of V+Nb produced the optimum combination of strength and toughness with ferrite-pearlite structure of the medium carbon steel by the A.C. method. 831MPa in UTS and 52.1J in toughness were obtained for 0.40c+0.12V+0.07Nb. It was martensite structure for the low carbon steel by the D.Q. method. The highest UTS and toughness obtained by Mo additions were 855MPa and 108j by 0.12C+0.10V+0.03Nb+1.13Mo respectively. Especially, the toughness of the low carbon steel was twice better than that of the medium carbon steel. 110$0^{\circ}C$was more appropriate than 120$0^{\circ}C$ for the reheating and forging temperature and 1.$2^{\circ}C$ /s was the best cooling rate from the viewpoint of the strength and toughness. Multiple regression analysis was used to quantify the influence of the microalloyed elements, temperatures and cooling rates on the strength, toughness, austenite grain size, and the pearlite interlamellar spacing.

• Journal of the Korean earth science society
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• v.38 no.4
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• pp.293-302
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• 2017

A large number of stonefly nymph fossils were discovered from the Late Triassic Amisan Formation in the Boryeong region, Korea. These Plecoptera were classified as Platyperlidae, Baleyopterygidae, and Siberioperlidae based on their external morphologies. The Baleyopterygidae were most abundant among the fossils. This suggests that the plecopteran has already been widely distributed in the Northeast Asian region including Russia, Mongolia and China during the Mesozoic. The fossils of these stoneflies imply that benthic habitats of flowing and fresh waters may have existed, given the fact that they are similar with the biology of extant species. These Plecoptera were found together with Ephemeroptera and Conchostraca and thus, they were presumed to be preying on these insects.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.25-29
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• 1998

일반적으로 동일한 배합에서 콘크리트의 강도를 증진시키는 방법중에서 혼화재를 넣는 방법이 일반적이다. 이는 첨가된 혼화재의 양만큼 생산비용이 증가하며, 본 실험에서 콘크리트 강도를 증진시키기 위해 사용한 자화수는 자석을 통과시켜 만든 물이며 제작방법 이 매우 간편하고 자석이라는 비소모성 및 무동력의 장치를 사용하여, 또한 화학물질을 사 용하지 않고 얻을 수 있다. 이때의 자화수는 외관상으로는 보통물과 아무런 차이가 없으며 무색무취이다. 즉 강력한 자장속에 보통 물을 통과시켜서 이온화된 자화수를 얻을 수 있을 것이다. 실례로 러시아 "샤프스쿠스크" 철근 콘크리트 제품공장에서는 자화수를 사용해서 매년 약 15%의 시멘트절약에 성공하고 있고, 모스크바의 철근콘크리트연구소에서 자주 자 화수의 전문회의가 열리며, 매번 좋은 결과를 서로 보고하고 있다고 한다. 본 실험에서는 자 화수에 의한 강도증진효과를 보기 위해서 동일배합에서 보통물과 자화수를 배합수로 하여 각각의 콘크리트 공시체를 제작해 압축강도를 비교하였다. 그 결과 보통물을 사용해 제작한 공시체 보다 4~13% 가량 강도증진효과를 보았다. 따라서 다른 혼화재를 사용하지 않고 오 직 자화수를 배합수로 하여 제작된 콘크리트 강도를 높임으로써, 동일한 배합강도를 얻기 위해서 보통물을 배합수로 제작된 콘크리트에 비해 시멘트 사용량을 줄일 수 있어 이에 따 른 경제적 효과를 얻을 수 있다고 본다. 이에 따라 본 연구는 여러 가지변수에 따라 자화수 가 콘크리트 강도증진에 어떠한 영향을 주는지를 알아보았다.는지를 알아보았다.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.101-104
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• 2008

The cost of repairing the deterioration of concrete structures due to corrosion of the reinforcement steel has been the prominent figure in the maintenacne of the reinforced-concrete infrastructures. As an alternative material to steel reinforcement, the use of Fiber Reinforced Polymer (FRP) bar in concrete is being actively studied for the high resistance of chemical environment and high strength to weight ratio properties of FRP. However, there remain various aspects of FRP properties that still need to be studied before the standard design criteria can be established. One of the imminent issues is the bond between FRP and concrete. In this study, the bond-behavior of FRP bars in concrete is investigated via the pullout test with three varying parameters: surface condition of FRP bars, concrete compression strength, and cyclic loading patterns. As a result of experiment, the bond strength of GFRP increased with the concrete compression strength increasing and decreased with applying cyclic load.

• Journal of the Korea Institute of Building Construction
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• v.23 no.6
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• pp.727-738
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• 2023

In concrete, the interface between the aggregate and cement paste is often the most critical factor in determining strength, representing the weakest zone. Lightweight aggregate, produced through expansion and firing of raw materials, features numerous surface pores and benefits from low density; however, its overall aggregate strength is compromised. Within concrete, diminished aggregate strength can lead to aggregate fracture. When applying lightweight aggregate to concrete, the interface strength becomes critical due to the potential for aggregate fracture. This study involved coating the surface of the aggregate with blast furnace slag fine powder to enhance the interfacial strength of lightweight aggregate. The impedance of test specimens was measured to analyze interface changes resulting from this surface modification. Experimental results revealed a 4% increase in compressive strength following the coating of the lightweight aggregate surface, accompanied by an increase in resistance values within the impedance measurements corresponding with strength enhancement.

• Journal of Adhesion and Interface
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• v.2 no.4
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• pp.32-38
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• 2001

Effects of the ratio of rubber composition on covulcanization and ozone resistance were studied in this study. Specimens used in this study were rubber compounds(specimen-A) blended with various ratio of NR, SBR, BR, IIR, and EPDM, unsaturated rubber compounds(specimen-B) with NR/BR/SBR, and saturated rubber compounds(specimen-C) with NR/IIR/EPDM. PAD adhesion specimen was prepared from vulcanizing specimen-A and B, and specimen-A and C, respectively. Using same adhesion specimen, peel strength was measured and tested ozone resistance. In specimen-A, peel strength was higher with increasing NR ratio for NR and BR contained blends. In other specimen-A containing NR and SBR, the peel strength was also increased with increasing SBR ratio. NR/BR/IIR/EPDM rubber compounds had also better adhesion property than NR/SBR/IIR/EPDM compounds. As more unsaturated rubber was blended, the peel strength was higher but ozone resistance was worse. Optimum ratio of unsaturated and saturated rubbers for the peel strength and ozone resistance was 60/40.

• Journal of the Korean Wood Science and Technology
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• v.41 no.4
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• pp.293-301
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• 2013

This study discusses the feasibility of coffee bean residue as a raw material of medium-density fiberboard (MDF). In this relation, the effect of coffee bean residue known as an absorbent material on the physical and mechanical properties of MDF manufactured at its different addition level. Coffee bean residue which is a by-product of coffee mill and large amount of waste left over after processing for instant coffee was added at the level of 3, 6, and 9% on dry basis and urea formaldehyde resin was used as the adhesive. The MDF made with mixture of wood fiber and coffee bean residue was tested for physical and mechanical properties as well as formaldehyde emission. The bending strength and internal bonding strength of the MDF made with mixture of wood fiber-coffee bean residue were higher than that of the KS standard in randomized mat structure type, but not in layered mat structure type. Also, the physical properties of MDF made with mixture of wood fiber-coffee bean residue showed a considerable improvement in thickness swelling over the commercial MDF. More importantly, the formaldehyde emission rate of MDF made with mixture of wood fiber-coffee bean residue met the KS standard and was close to that of commercial MDF. These results showed the feasibility of coffee bean residue as a raw material for the production of environmentally-friendly MDF. Additional works on adhesive-coffee bean compatibility, improvement of moisture absorption effect and reduction the formaldehyde emission rate by carbonization of coffee bean residue may be required.