• Advances in concrete construction
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• 제6권6호
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• pp.645-658
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• 2018

Despite being one of the most abundantly used construction materials because of its exceptional properties, concrete is susceptible to deterioration and damage due to various factors particularly corrosion, improper loading, poor workmanship and design discrepancies, and as a result concrete structures require retrofitting and strengthening. In recent times, Fiber Reinforced Polymer (FRP) composites have substituted the conventional techniques of retrofitting and strengthening of damaged concrete. Most of the research studies related to concrete strengthening using FRP have been performed on undamaged test specimens. This contribution presents the results of an experimental study in which concrete specimens were damaged by mechanical loading and elevated temperature in laboratory prior to application of Carbon Fiber Reinforced Polymer (CFRP) sheets for strengthening. The test specimens prepared using concrete of target compressive strength of 28 MPa at 28 days were subjected to compressive and splitting tensile testing up to failure and the intact pieces of the failed specimens were collected for the purpose of repair. In order to induce damage as a result of elevated temperature, the concrete cylinders were subjected to $400^{\circ}C$ and $800^{\circ}C$ temperature for two hours duration. Concrete cylinders damaged under compressive and split tensile loads were re-cast using concrete and rich cement-sand mortar, respectively and then strengthened using CFRP wrap. Concrete cylinders damaged due to elevated temperature were also strengthened using CFRP wrap. Re-cast and strengthened concrete cylinders were tested in compression and splitting tension. The obtained results revealed that re-casting of specimens damaged by mechanical loadings using concrete & mortar, and then strengthened by single layer CFRP wrap exhibited strength even higher than their original values. In case of specimens damaged by elevated temperature, the results indicated that concrete strength is significantly dropped and strengthening using CFRP wrap made it possible to not only recover the lost strength but also resulted in concrete strength greater than the original value.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 추계 학술논문 발표대회
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• pp.9-10
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• 2017

For the structural analysis of reinforced concrete structures, the mechanical properties of concrete at each temperature are required and the mechanical property values according to specific temperature are presented in the design regulations and codes. In this study, the mechanical properties of concrete were experimented by using 35MPa concrete produced in Korea from 20℃ to 900℃(two kinds of test method). Compared the results with previous domestic papers, we aimed to contribute to the construction of mechanical characteristics D.B. of at the elevated temperatures of domestically produced concrete which can be used for structural analysis in fire.

• 한국해양공학회지
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• 제25권4호
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• pp.12-17
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• 2011

Little design data is available for the creep life prediction of 9% Ni alloy in elevated temperatures. Therefore, in this study, a series of creep tests under 16 combined conditions with 4 kinds of stresses and 4 temperatures was performed to obtain creep design and life prediction data for 9% Ni alloy, with the following results. The stress exponents decreased as the test temperature increased. The creep activation energy gradually decreased as the stresses became larger. The Larson-Miller parameter (LMP) constant for this alloy was estimated to be about 2.

• Nuclear Engineering and Technology
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• 제41권10호
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• pp.1323-1332
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• 2009

The IHX (Intermediate Heat eXchanger) for a pool-type SFR (Sodium-cooled Fast Reactor) system transfers heat from the primary high temperature sodium to the intermediate cold temperature sodium. The upper structure of the IHX is a coaxial structure designed to form a flow path for both the secondary high temperature and low temperature sodium. The coaxial structure of the IHX consists of a central downcomer and riser for the incoming and outgoing intermediate sodium, respectively. The IHX of a pool-type SFR is supported at the upper surface of the reactor head with an IHX support structure that connects the IHX riser cylinder to the reactor head. The reactor head is generally maintained at the low temperature regime, but the riser cylinder is exposed in the elevated temperature region. The resultant complicated temperature distribution of the co-axial structure including the IHX support structure may induce a severe thermal stress distribution. In this study, the structural feasibility of the current upper support structure concept is investigated through a preliminary stress analysis and an alternative design concept to accommodate the IHTS (Intermediate Heat Transport System) piping expansion loads and severe thermal stress is proposed. Through the structural analysis it is found that the alternative design concept is effective in reducing the thermal stress and acquiring structural integrity.

• Steel and Composite Structures
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• 제8권3호
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• pp.179-200
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• 2008

This paper reports the results of a recent experimental study into the behavior of welded fin-plate connections to both hollow and concrete filled tubular (CFT) columns under shear. Experiments have been performed at both ambient and elevated temperatures with the aid of an electric kiln. The observed failure modes include fracture of the fin plate and tearing out of the tube around the welds. By considering the results of previously published research, the current design method for similar connections under purely tensile load, in CIDECT Guide 9, based on a deformation limit of 3% of the tube width is shown to be inadequate when evaluating the ultimate strength of such connections. By comparing the results from the current test program which failed in the fin-plate with Eurocode guidance for failure of a fin-plate alone under shear and bending load it is shown that the column face influences the overall connection strength regardless of failure mode. Concrete in-fill is observed to significantly increase the strength of connections over empty specimens, and circular column specimens were observed to exhibit greater strength than similarly proportioned square columns. A finite element (F.E.) model, developed using ABAQUS, is presented and validated against the experimental results in order that extensive parametric tests may be subsequently performed. When validating the model against elevated temperature tests it was found that using reduction factors suggested in published research for the specific steel grades improved results over applying the generic Eurocode elevated temperature steel strength reduction factors.

• 대한기계학회논문집A
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• 제20권11호
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• pp.3415-3423
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• 1996

The compact tension specimen geometry has been widely used for measuring fatigue crack growth rates at elevated temperature when the fatigue load is under tension/tension condition. However, most of the elevated temperature components which have significant crack growth life experience fatigue load under tension/compression conditions. Thus test techniques are required since the compact tension specimen cannot be used for tension/compression loading. In this paper, a simplified test procedure for measureing fatigue crack growth rates is proposed, which employs a round bar specimen with a small surface crack. Fatigue crack growth rates under tension/ tension loading conditions at elevated temperature were measured according to the proposed procedure and compared with those previously measured by C/(T) specimens. Since both the measured crack growth rates were comparable, the fatigue crack growth rates under tension/ compression load can be reliably measured by the proposed procedure. For monitoring crack depth. DC electric potential method is employed and an optimal probe location and current input conditions were proposed.

• Steel and Composite Structures
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• 제43권3호
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• pp.341-351
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• 2022

This paper presents an inelastic buckling behavior analysis of rectangular hollow steel tubes with geometrical imperfections under elevated temperatures. The main variables are the temperature loads, slenderness ratios, and exposure conditions at high temperatures. The material and structural properties of steels at different temperatures are based on Eurocode (EN 1993-1-2, 2005). In the elastic buckling analysis, the buckling strength decreases linearly with the exposure conditions, whereas the inelastic buckling analysis shows that the buckling strength decreases in clusters based on the exposure conditions of strong and weak axes. The buckling shape of the rectangular steel column in the elastic buckling mode, which depicts geometrical imperfection, shows a shift in the position at which bending buckling occurs when the lower section of the member is exposed to high temperatures. Furthermore, lateral torsional buckling occurs owing to cross-section deformation when the strong axial plane of the model is exposed to high temperatures. The elastic buckling analysis indicates a conservative value when the model is exposed to a relatively low temperature, whereas the inelastic buckling analysis indicates a conservative value at a certain temperature or higher. The comparative results between the inelastic buckling analysis and Eurocode 3 show that a range exists in which the buckling strength in the design equation result is overestimated at elevated temperatures, and the shapes of the buckling curves are different.

• 한국강구조학회 논문집
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• 제28권4호
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• pp.253-261
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• 2016

중심축 하중을 받는 고온상태 강재기둥의 압축강도를 해석하기 위하여 새로운 유한요소 해석모델을 제시하였으며, 기존 연구를 대상으로 해석가정 및 유한요소해석 기법을 비교 분석하였다. 또한 유한요소 해석결과를 바탕으로 새로운 고온상태 강재 기둥의 설계식을 제안하였으며, 해석결과 및 실험연구 결과와 비교하였을 때 AISC와 EC3 설계식보다 본 연구의 제안식이 고온상태 강재기둥의 압축강도를 정확하게 표현하는 것을 확인하였다.

• 한국정밀공학회지
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• 제33권8호
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• pp.691-695
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• 2016

This paper covers the investigation of the microscale behavior of Pt nanostrucures fabricated by atomic layer deposition (ALD) at elevated temperature. Nanoparticles are fabricated at up to 70 ALD cycles, while congruent porous nanostructures are observed at > 90 ALD cycles. The areal density of the ALD Pt nanostructure on top of the SiO2 substrate was as high as 98% even after annealing at $450^{\circ}C$ for 1hr. The sheet resistance of the ALD Pt nanostructure dramatically increased when the areal density of the nanostructure decreased below 85 - 89% due to coarsening at elevated temperature.

• 한국안전학회지
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• 제28권3호
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• pp.18-22
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• 2013

The Co-base super heat resisting alloy ECY768 is employed in gas turbine because of its high temperature strength and oxidation resistance. The prediction of fatigue life for superalloy is important for improving the efficiency. In this paper, low cycle fatigue tests are performed as variables of total strain range and temperature. The relations between strain energy density and number of cycle to failure are examined in order to predict the low cycle fatigue life of ECY768 super alloy. The lives predicted by strain energy methods are found to coincide with experimental data and results obtained from the Coffin-Manson method. The fatigue lives is evaluated using predicted by Coffin-Manson method and strain energy methods is compared with the measured fatigue lives at different temperatures. The microstructure observing was performed for how affect able to low-cycle fatigue life by increasing the temperature.