• Magazine of the Korea Concrete Institute
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• v.10 no.3
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• pp.117-124
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• 1998

본 연구는 고성능 철근콘크리트 보의 연성능력에 관한 실험이다. 실험변수로는인장철근비( )와 하중재하형태(1점가력과 2점가력)가 있다. 콘크리트의 실린더 압축강도가 800-900㎏/㎠, 슬럼프 20∼25㎝ 및 슬럼프 플로우가 60∼70㎝인 고성능 철근콘크리트 보의 휨 실험 결과,고성능 콘크리트는 일반강도 콘크리트보다 취성적인 성질을 나타냈으며, 이러한 성질은 고성능 콘크리트의 연성능력을 감소시켰다. 고성능철근콘크리트의 경우 등가응력블록 변수는 MacGregor블록이나 New Zealand 규준을 사용하는 것이 바람직하다. 또한, 극한 곡률을 구할때는 cu= 0.0042값을 사용하는 것이 타당하다고 사료된다. 고성능 철근콘크리트 보의 경우, 현재 ACI 규준의 철근비에서 허용하는 2 및 4 이상의 연성지수 확보는 각각 '/ 0.30 범위에서 정적하중 상태의 경우 철근비가 - '=0.60 b이하에서 가능하고 휨 부재의 모멘트 재분배를 위한 경우는 철근비를 - '=0.33 b이하로 낮추어야 할 것으로 판단된다.

• Journal of the Korea Institute of Building Construction
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• v.19 no.3
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• pp.201-207
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• 2019

In this study, the direct tensile properties of amorphous metallic fiber-reinforced cement based composites according to the strain was evaluated. A thin plate-shape amorphous metallic fiber with 15mm and 30mm in length was used. And fiber-reinforced cement based composites were prepared with contents of 1.0, 1.5, 2.0%. The direct tensile test was conducted under the conditions of $10^{-6}/s(static)$ and $10^1/s(dynamic)$ strain rate. As a results, amorphous metallic fiber with a length of 15mm was observed in pull-out behavior from the cement matrix because of the short fiber length and large portion of mixed fiber. On the other hand, amorphous metallic fiber with a length of 30mm were not pulled out from matrix because the bonding force between the fiber and matrix was large due to rough surface and large specific surface area. However, fracture occurred because thin plate shape fibers were vulnerable to shear force. Tensile strength, strain capacity and toughness were improved due to the increase in the fiber length. The dynamic increase factor of L15 was larger that of L30 because the bonding performance of the fiber-matrix interface is significantly affected by the strain rate.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.173-185
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• 1988

This study is intended to investigate the shear fatigue behaviour of reinforced concrete beams based on a series of experiments, and verify the test results in comparison with the analysis result obtained by using a nonlinear finite element method. The experiments are divided into the tests under the static loading and the test under the dynamic fatigue loading. In order to investigate the shear failure behaviour under static loadings, four specimens for three different cases were made and tested. The behaviour of stirrups with the static stress and strain variations were observed based on the results of these tests. In the fatigue fracture tests, eleven specimens for four different cases were made and tested. Various observations on mid-span deflection of test beams and tensile strains of reinforcing steels as well as stirrups were made against various fatigue loadings. It may be concluded that the shear fatigue strengths of R.C. specimens at one million cycles turn out to be approximately 65 percent of the static ultimate shear strength.

• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.377-385
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• 2003

Flexural characteristics of the R.C beams strengthened with newly-developed grid-type carbon fiber plastics(CFRP-GRIDS) were investigated. The tests were conducted under the four-points load to the failure to investigate the strengthening effects of CFRP-GRIDS on the beams. Results showed that initial cracks appeared in the boundary layers of fibers embedded in the newly-placed mortar concrete slowly progressed to the direction of supports and showed fracture of fiber plastics and brittle failure of concrete in compression in sequence after the yielding of steel reinforcement. Accordingly, the appropriate area of Grid-type carbon-fiber plastics in the strengthening design of deteriorated RC structures should be limited and given based on the ultimate strength design method to avoid the brittle failure of concrete structures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.9
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• pp.2402-2408
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• 2009

This study conducted a static tensile test in order to prevent the lowering of load carrying capacity caused by critical sections made by over bolt holes in the base plate and the cover plate of steel member joints using high-tension bolts. The change of the load carrying capacity of joints was examined by comparison of the maximum load on joint fracture obtained from the tensile test with critical section rate and design strength. According to the results, the rate of decrease in strength was higher when the critical section rate was high, and in particular, decrease in strength was affected much more by critical sections in the base plate than by those in the cover plate. In high-tension bolt joints using over bolt holes for the base plate and the cover plate, load carrying performance was somewhat lower than that in joints using standard bolt holes, but the maximum tensile strength on facture was over 15% higher than design fracture strength. According to the results of this study, the use of over bolt holes in high-tension bolt joints had an insignificant effect on the lowering of load carrying capacity, so the allowance of over bolt holes in the joints of steel members is expected to enhance to the economy and efficiency of the works.

• Journal of the Korea Institute of Building Construction
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• v.19 no.6
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• pp.495-501
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• 2019

Recently, research has been carried out into the use of carbon fiber reinforced polymer (CFRP), which has good tensile strength and corrosion resistance, as an alternative to rebar. But as of yet, the research into fatigue failure of CFRP is insufficient. In this paper, an analysis was performed of the mechanical behavior and failure patterns of CFRP reinforced concrete beams according to static and cyclic loads, in order to evaluate the safety and validity of CFRP rebar as an alternative material for rebar. The cyclic load ranged from 10 % to 70% of the ultimate load, and was loaded at a speed of 3Hz using a sine wave in the form of a three-point loading method. Through the static load test, the maximum load or stiffness of the beam was found to increase remarkably with the increase of the reinforcement, but the fatigue test showed that the number of repetitions decreased and the amount of deflection increased with the increase of the reinforcement.

• Journal of the Society of Disaster Information
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• v.13 no.3
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• pp.313-321
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• 2017

In order to investigate the basic performance of the high strength anchor for asphalt road subjected to tensile load, the static pullout test was carried out and the pullout strength of the asphalt anchor was analyzed. In the pullout test, the depth of anchor, depth of pavement, diameter of anchor, type of anchor, experimental temperature, epoxy type and amount of anchor were used as test variables. As a result, the steel strength of asphalt anchor was 1.08 times higher than that of conventional concrete anchor, therefore it is considered appropriate to use the steel strength formula of concrete anchor for asphalt anchor. Compared with the proposed formula, the pullout load obtained from the test of the asphalt anchor was within ${\pm}10%$. The ratio of the projected area of the asphalt anchor is similar as that of the concrete anchor.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.20 no.1
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• pp.49-59
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• 1984

Optimizing investigation of characteristics of underwater welding by a gravity type arc welding process was experimentally carried out by using six types of domestic coated welding electrodes for welding of domestic marine structural steel plates (KR Grade A-1, SWS41A, SWS41B,) in order to develop the underwater welding techniques in practical use. Main results obtained are summarized as follows: 1. The absorption speed of the coating of domestic coated lime titania type welding-electrode became constant at about 60 minutes in water and it was about 0.18%/min during initial 8 minutes of absorption time. 2. Thus, the immediate welding electrode could be used in underwater welding for such a short time in comparison with the joint strength of in-atmosphere-and on-water-welding by dry-, wet-or immediate-welding-electrode. 3. By bead appearance and X-ray inspection, ilmenite, limetitania and high titanium oxide types of electrodes were found better for underwater-welding of 10 mm KR Grade A-1 steel plates, while proper welding angle, current and electrode diameter were 6$0^{\circ}C$, above 160A and 4mm respectively under 28cm/min of welding speed. 4. The weld metal tensile strength or proof stress of underwater-welded-joints has a quadratic relationship with the heat input, and the optimal heat input zone is about 13 to 15KJ/cm for 10mm SWS41A steel plates, resulting from consideration upon both joint efficiency of above-100% and recovery of impact strength and strain. Meanwhile, the optimal heat input zone resulting from tension-tension fatigue limit above the base metal's of SWS41A plates is 16 to 19KJ/cm. Reliability of all the empirical equations reveals 95% confidence level. 6. The microstructure of the underwater welds of SES41A welded in such a zone has no weld defects such as hydrogen brittleness with supreme high hardness, since the HAZ-bond boundary area adjacent to both surface and base metal has only Hv400 max with the microstructure of fine martensite, bainite, pearlite and small amount of ferrite.

• Journal of the Korea Concrete Institute
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• v.22 no.6
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• pp.777-786
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• 2010

This paper examines the flexural behavior of full-scale prestressed concrete girders that were constructed of steel fiber reinforced ultra high performance concrete (UHPC). This study is designed to provide more information about the bending characteristics of UHPC girders in order to establish a reasonable prediction model for flexural resistance and deflection for future structural design codes. Short steel fibers have been introduced into prestressed concrete T-girders in order to study their effects under flexural loads. Round straight high strength steel fibers were used at volume fraction of 2%. The girders were cast using 150~190 MPa steel fiber reinforced UHPC and were designed to assess the ability of steel fiber reinforced UHPC to carry flexural loads in prestressed girders. The experimental results show that steel fiber reinforced UHPC enhances the cracking behavior and ductility of beams. Moreover, when ultimate failure did occur, the failure of girders composed of steel fiber reinforced UHPC was observed to be precipitated by the pullout of steel fibers that were bridging tension cracks in the concrete. Flexural failure of girders occurred when the UHPC at a particular cross section began to lose tensile capacity due to steel fiber pullout. In addition, it was determined that the level of prestressing force influenced the ultimate load capacity.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.85-85
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• 2017

무동력 복합작업기는 치즐쟁기와 디스크의 배열에 따라 작업성능이 좌우된다. 프레임과 디스크, 치즐쟁기에 가해지는 기본적인 힘의 상태를 확인하기 위한 정적 구조해석을 수행하였다. 복합작업기는 디스크는 $18^{\circ}$가 경사진 형태로 전면9개 후면9로 총 18개, 치즐쟁기(Chiselplow)는 4개로, 디스크는 모두 18개이다. 정적인 상태에서 끄는 견인력은 100마력, 150마력, 200마력으로 하였으며 Inventor의 해석 시스템은 힘을 N으로 사용하기 때문에 각 마력에 부가되는 하중을 N으로 치환하여 사용하였다. 구속조건은 frame과, disc, chisel plow에 맞닿는 면을 구속하고, 힘의 방향은 프레임과 트랙터의 연결면, 디스크 날과 땅의 접촉면에 적용했다. front /rear 디스크는 이론상으로는 양 디스크가 쌍으로 마주하고 있어서 스캔데이타를 중심으로 모델링한 결과를 바탕으로, 전후면 디스크해로우의 해석을 수행하였다. 조립 또는 사용상의 문제점이나 자연적인 유격에 의해 어느 정도 대칭이 되지 않을수 있으나 그 정도에 따라 진동과 내구성에 문제가 될 수도 있기에 한쌍에 대해 모델링을 통한 해석을 수행하였다. 해석결과에 따르면 디스크에 작용하는 폰미세스 응력은 극한강도에 미치지 않은 것으로 나타났으며 Frame의 최대 폰 미세스 응력을 제외하면, 대부분의 응력은 항복강도에 현저히 미치지 못하는 수치이고, 프레임의 경우는 150마력, 200마력으로 힘을 가할 때 항복강도는 넘는 수치이지만 극한인장강도에는 미치지 못하는 수치인 것을 알 수 있었다. 100마력에 폰 미세스 응력의 최대값은 0.161918 MPa이고 프레임 강의 항복강도인 207MPa와 디스크의 항복강도인 250MPa에 못 미치는 수치이다. 150마력과 200마력의 힘으로 회전할 때의 폰 미세스 응력의 최대값은 0.286425MPa과 0.381921 MPa로 항복강도인 250MPa에 크게 못 미치는 수치이다. 그 이유는 디스크해로우 방식의 복합작업기는 견인저항력이 작게 설계되고 작업속도를 개선하기 위한 목적으로 사용되기 때문으로 사료된다. 벤치마킹 기대의 Rear 디스크도 마찬가지로 각도는 $18^{\circ}$이며, 동일한 구속조건을 적용하여 시뮬레이션을 수행하였으며 해석결과는 모두 항복강도 이내로 예측 되었다. 디스크에 최대로 응력이 미치는 부분은 디스크와 프레임이 연결되는 허브 부분이다. 각도가 커짐에 따라 응력이 증가하므로 이를 감안한 설계인자 도출이 가능하다. 마력과 각도가 증가함에 따라 디스크 해로우에 작용하는 폰미세스 응력과, 접촉압력이 증가하므로 이에 대한 검토와 동적하중인 로드프로파일을 적용한 해석을 수행하여 내구수명 특성에 대한 연구를 수행할 계획이다.