• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.71-76
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• 1994

Recently, constructions of huge reinforced concrete structures such as nuclear power stations have been increased. When massive concrete is placed, cracking due to the hydration heat of cement is recognized as a major problem. The development of thermal stress is influenced by the structure shape and the constraint conditions, and cracks usually occure from tensile stresses which developed due to temperature drop. In this study a protocol specimen is made to examine the distribution of temperature and thermal stress of reaction wall of Daewoo Institute Construction Technology. The size of the specimen is made by considering minimum size of real structure. In this study, concrete strain gauge, concrete stress gauge, concrete non-stress gauge, and thermocouples, are instrumented to measure thermal stress in massive concrete structure. A new measuring technique is proposed to calculate thermal stress.

• 콘크리트학회지
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• 제7권2호
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• pp.126-135
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• 1995

온도균열은 시멘트의 수화열에 의한 온도응력이 콘크리트의 인장강도보다 커질 경우에 발생하는 균열로서, 구조물의 수밀성과 기밀성등에 중대한 영향을 미치기 때문에 매스콘크리트와 같이 단면이 큰 구조물의 설계 및 시공시에는 반드시 온도균열에 대한 배려가 필요하다. 본 연구에서는 모의실험체를 대상으로 하여 매스콘크리트의 경화시 발생하는 온도응력을 측정할 목적으로 콘크리트변형계와 무응력계 그리고 유효응력계등을 설치하여구조물 내부의 온도응력의 경시변화를 검토하고 콘크리트변형계를 이용한 온도응력 산정방법 및 문제점등에 대하여 검토하였다. 연구결과 콘크리트변형계와 무응력계를 이용한 새로운 온도응력 산정법을 제시하였으며, 그 결과 유효응력계의 측정치와 거의 일치하는 값을 얻을 수 잇었다. 이를 위해서는 무응력계 또는 이와 동일하게 초기재령시의 콘크리트 자기수축변형률을 측정할 수 있는 게이지의 설치가 전제가 되어야 하며, 초기재령시의 건조수축량에 대한 정량화가 가능하다면 콘크리트변형계를 이용한 온도응력의 산정도 충분히 가능하다는 것을 알 수 있다.

• Journal of Welding and Joining
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• 제21권1호
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• pp.66-71
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• 2003

The release of residual stress by mechanical loading and unloading is often performed in the fabrication of box structure fur steel bridge. The proper degree of loading and unloading is significant at release method of residual stress by mechanical loading because that degree is changed by material and geometric shape of welded structure. Therefore, the simulation model that could exactly analyze the release of residual stress by mechanical loading is to be necessary. In this study, the non-linear behavior of weldments under external loading and unloading, such as the decrease and increase of structure stiffness, was investigated by monitoring of nominal stress and strain. Tensile loading and unloading test and the proper degree of stress relaxation was measured by sectioning technique using strain gauge. Analysis model that is indispensable for the effective application of MSR method was established on the basis of test and measurement result.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.229-230
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• 2023

In this study, the hydration heat differential method was applied to mass concrete structures, and the hydration heat analysis was compared and analyzed with on-site measurement results. The results showed that the temperature history measurements of mass concrete were managed at a difference of 8.4 ℃, and although there was some deviation in thermal stress, a similar trend was observed. Consequently, it was determined that the thermal stress on the surface of mass concrete is less than its tensile strength, which would prevent the occurrence of thermal cracks.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.825-831
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• 2010

In this study is stress behavior of steel support structure is to identify basic research. Steel stress due to load step to determine the behavior of steel using strain gauge steel loading test was performed. Numerical analysis and steel loading test using strain gauge on the actual steel stress behavior was analyzed. First, when tensile loading 3.5tonf load side of the plastic behavior appeared. Elastic model, using numerical analysis and comparison of results, the actual value is saved and you can see some difference. This repeated loading tests on steel can be seen from the results of the stress behavior of the steel rather than the elastic behavior of elastic-plastic behavior is because you can see. In addition, the upper and lower steel stress in compression and tension behavior represents the behavior was similar, but different. Steel loading test results, Y-axis get a compression if X-axis is tension. The future based on this study, the stress sensitivity curve of magnetic anisotropy sensor for non-destructive stress measurement technique for the study will be performed. And the behavior of plastic zone and residual stress to determine the numerical analysis using non-elastic model is needed.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.372-377
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• 2002

Residual stress by welding should be reduced because that decreases the reliability on strength of welded structure. The reason is that the total stiffness of structure decreases by non-linear behavior of weldment under external load. The release of residual stress by mechanical loading and unloading is often performed in the fabrication of box structure for steel bridge. The proper degree of loading and unloading is significant at release method of residual stress by mechanical loading because that degree is changed by material and geometric shape of welded structure. Therefore, the simulation model that could exactly analyze the release of residual stress by mechanical loading is to be necessary. This simulation model should be established on the based of variable and accurate measurement data. In this study, the non-linear behavior of weldments under external loading and unloading, such as the decrease and increase of structure stiffness, was investigated by monitoring of nominal stress and strain. Tensile loading and unloading test under variable load was performed and the proper degree of stress relaxation was measured by sectioning technique using strain gauge.

• International Journal of Korean Welding Society
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• 제2권1호
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• pp.40-44
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• 2002

Residual stress by welding should be reduced because that decreases the reliability on strength of welded structure. The reason is that the total stiffness of structure decreases by non-linear behavior of weldment under external load. The release of residual stress by mechanical loading and unloading is often performed in the fabrication of box structure for steel bridge. The proper degree of loading and unloading is significant at release method of residual stress by mechanical loading because that degree is changed by material and geometric shape of welded structure. Therefore, the simulation model that could exactly analyze the release of residual stress by mechanical loading is to be necessary. This simulation model should be established on the based of variable and accurate measurement data. In this study, the non-linear behavior of weldments under external loading and unloading, such as the decrease and increase of structure stiffness, was investigated by monitoring of nominal stress and strain. Tensile loading and unloading test under variable load was performed and the proper degree of stress relaxation was measured by sectioning technique using strain gauge.

• 콘크리트학회논문집
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• 제11권6호
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• pp.3-12
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• 1999

The larger, loftier and more highly strengthened the recent structures become, the greater attention is paid to the problem of thermal crack occurrence associate with hydration heat. As one of methods to solve the problem, a care has been taken to the improvement of construction such as the application of pre-cooling or pipe-cooling, adjustment of concrete block size, concrete placement timing, joint arrangement and so on. But it is expected that a proper selection of cement shall additionally contribute to the control of thermal cracks. In this study, thus, we selected 4 types of cements such as Type V for anti-sulphate, blast furnace cements (slag content of 45% and 65% respectively)and ternary blended low heat cement, and carried out mock-up tests. In every assigned time, temperatures and thermal stresses were measured and calculated from raw data. As a result of measurement, it was found that the magnitude of hydration heat is in order of blast furnace slag cement. Type V and ternary blended low heat cement. Results of thermal stresses were same as the order of temperature. In addition, thermal stresses calculated from the data of strain gauges showed almost similar to those measured from effective stress gauges only when strain values were adjusted properly in accordance with initial time of stress appearance. Theoretical results agreed well with the measured values comparatively, but showed slight differences. It is inferred that these differences shall be reduced if more tests capable of evaluating thermal characteristics of concrete are carried out.

• 한국산학기술학회논문지
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• 제1권1호
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• pp.23-26
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• 2000

스폿용접은 겹침판을 끼우고 가압상태의 전극 사이에 단시간의 대전류를 흘려, 전류가 집중하는 전극 직하의 모재 저항발열과 전극 및 모재의 열전도를 이용해서 판과 판의 접촉부에 안정한 용융부를 형성하는 압접법이다. 스폿용접으로 대표되는 저항용접법의 특징은 작업속도가 빠르고. 대량 생산적인 성격이 강하다는 점이다. 그러나, 용접부의 점검이 중요함에도 불구하고 용접부의 직접 감시가 곤란하여 적절한 검사 방법이 확립되지 않은 결점이 있다. 최근 제조공정 중에 실시간으로 스폿 용접부를 비파괴적인 방법을 이용하여 응력 및 변형상태를 체크하고. 결합을 검출할 수 있는 방법이 강력히 요구되고 있는 실정이다. 스폿 용접부페 광학적으로 레이저 빔을 조사하여 렌즈에 의해 결상되면 결상면상에 작은 입자모양의 반점이 생긴다. 이 반점을 스페클이라 하며 이 스페클에 의해 만들어진 불규칙한 반점모양을 스페클 패턴이라 한다. 이러한 현상은 레이저 빔이 가간섭의 성질을 지니고 있으므로 조사영역에서는 랜덤하지만 시간적으로 정상적인 위상관계에 있는 다수의 광파가 간섭함으로서 발생하는데 이와 같은 줄무늬 간격을 PC 프로그램으로 계산하여 응력을 측정한다. 따라서 본 연구에서는 레이저를 이용한 전자처리식 스페클 패턴 간섭법(ESPI)으로 스폿 용접부의 응력 및 변형률을 측정하여 스트레인 게이지법과 비교 고찰한 결과, ESPI법이 유용함을 알 수 있었으며. 이 방법을 생산 공정에 적용함으로서 생산성 및 품질 향상을 기할 수 있다고 판단된다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.713-716
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• 2002

The dimensional accuracy of the cold forged products is strongly dependent on the elastic behavior of the die. The elastic deformation of the die is continuously changed during the process. Therefore, it is needed to measure the deformation of die. Strain gauges are used to measure the elastic strains in the die during cold backward extrusion process. The strain gauges are attached on the die surface and embedded at the interface between the die insert and the stress ring. In order to compare the results with the FE-analysis, the rigid-plastic FE-analysis of cold backward extrusion process using DEFORM-3D has been performed, and the analysis of elastic deformation of the die has been done by using ANSYS with non-linear contact.