• Journal of Welding and Joining
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• v.12 no.1
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• pp.73-79
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• 1994

Low cycle fatigue test was performed by companion specimens method to compare the properties of cyclic strain for the weldments of controlled rolling steel CR60 and welding structural steel SM58Q. And the result does not showed any difference of low cycle fatigue life between weldments. Especially, the values of coefficient of cyclic plastic strain $C_{p}$ and exponent of cyclic plastic strain $K_{p}$ of heat affected zones of CR60 steel and SM58Q steel were same. And $C_{p}$ and $K_{p}$ of CR60 steel were equal to the values of weld it means a good combination between the base metal, the heat affected zone and the weld of CR60 steel.eel.eel.

• Journal of Korean Society of Steel Construction
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• v.15 no.4 s.65
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• pp.369-378
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• 2003

This study proposed a damage index for steel members and examined a process where steel square tubular columns under cycle loading failed to meet the damage index. A nonlinear analysis was carried out and a damage process analyzed using a finite element program. Material properties and strain characteristics were obtained from material testing. The effect on the damage of members was analyzed according to varying kinds of steels and conditions of loading based on material testing results. According to strain characteristics and cumulative plastic strain of each variable, the effect of conditions of loading and kinds of steels on the damage could be estimated quantitatively.

• Journal of Korean Society of Steel Construction
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• v.14 no.5 s.60
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• pp.613-625
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• 2002

This paper aimed to investigate the damage process of steel parts experiencing failure under strong repeated loading. Likewise, a damage index using various factors related to the damage was proposed. An analysis method for evaluating the damage state was also developed. The damage assessment method focused on the local strain history at the cross-section of the heaviest concentration of deformation. Cantilever-type steel parts were analyzed under uniaxial load combined with a constant axial load, considering horizontal displacement history, Loading patterns and steel types were considered as the main parameters in analyzing the models. The effects of the parameters on the failure modes, deformation capacity, and damage process as seen from the analysis results were also discussed. Each failure process was compared as steel types. In addition, the failure of steel parts under strong repeated loading was determined according to loading. Results revealed that the state of the failure is closely related to the local plastic strain.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.2
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• pp.73-82
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• 2000

본연구의 목적은 반복하중을 받는 철근콘크리트 교량 교각의 비선형 이력거동을 해석적으로 예측하는 것이다 이를 위해서 반복적인 횡하중이 작용하는 경우에 실험결과와 일치하는 교각의 하중-변위 이력곡선을 도출하고자 수정된 trilinar 이력거동모델을 이용하였다 철근과 콘크리트의 비선형 거동특성과 각 하중단계에 따른 교각의 중립축을 구하여 소성힌지부의 모멘트와 변형률을 구하고 반복하중하에서의 강성의 변화를 해석적으로 모형화하기 위하여 각기 다른 강성을 갖는 5가지 지선을 갖춘 형태의 이력거동모델식을 제안하였다 본 연구에서는 실험적으로 구한 하중-변위 이력곡선을 이용하여 축하중비 주철근비 및 구속철근비에 따른 강도감소지수와 강성감소지수의 영향을 회귀분석을 이용하여 일반식으로 제안하였다 새로운 이력거동 해석 모델을 프로그램 SARCF III에 적용함으로써 기존 철근콘크리트 교각에 강도 및 강성감소 현상을 정확하게 예측하였다

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.195-204
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• 2004

A series of constant creep and repeated creep tests are performed to investigate the behavior of visco-elasto-plastic materials of chemical grouted sands. In the result of constant creep test, the material exhibits three types of shear strain : elastic, plastic, viscoelastic. The elastic, plastic and viscoelastic strains are linear, i.e., the strains are proportional to the stresses for loading. Good agreement is found between the predicted viscoelastic and test results by the power law and the generalized model. In the repeated creep test, the instantaneous recoverable strain is time-independent and the magnitude of accumulated plastic strain increases with number of cycles. Also it is seen that the accumulated plastic strains are approximately proportional to stress. There are no significant differences between test results predicted values for first cycle, and the differences increase relatively insignificantly with number of cycles.

• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.15-26
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• 2004

Based on an estimating method for post-cyclic strength and stiffness with cyclic triaxial tests proposed by one of the authors, cyclic Direct Simple Shear (DSS) tests were carried out to confirm whether the method can be adapted to DSS test on fine-grained soils: silty clay, plastic silt, and non-plastic silt. Results from cyclic and post-cyclic DSS tests were interpreted by a modified method as adopted for cyclic and post-cyclic triaxial tests. In particular, influence of plasticity index for fine-grained soils and initial static shear stress (ISSS) was emphasised. Findings obtained from the present study are: (i) liquefaction strength ratio of fine-grained soils decreases with decreasing plasticity index and increasing ISSS; (ii) plasticity index and ISSS did not markedly influence relation between equivalent cyclic stiffness and shear strain relations; (iii) the higher the plasticity index of fine-grained soils is, the less the strength ratio decreases with increment of a normalcies excess pore water pressure (NEPWP); (iv) stiffness ratio of plastic silt has large activity decrease rapidly with increasing excess pore water pressure; and (v) post-cyclic strength and stiffness results from DSS tests agree well with those predicted by the method modified from a procedure used for triaxial test results.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.339-353
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• 1998

In this paper, the previous damage models for structures and their components under seismic repeated loading were reviewed systematically. A failure criterion for steel members under severe cyclic excitations as in strong earthquakes was described. A new approach to seismic damage assessment for steel members was proposed. This method was based on a series of the experimental and numerical investigations for steel members under very low cyclic loading. In this study, very low cyclic loading means repetitive loading, 5 to 20 loading cycles, within the large plastic range. The proposed damage assessment method was focused on the local strain history at the cross-section of the most severe concentration of deformation.

• Geotechnical Engineering
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• v.11 no.1
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• pp.113-126
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• 1995

Both resonant column (RC) and torsional shear(TS) tests were performed at small to intermediate strain levels to investigate deformational characteristics of cohesive soils. The effects of variables such as strain amplitude, loading frequency, and number of loading cycles were studied. Plasticity index was found to be an important variables in evaluating these effects. Soils tested include undisturbed silts and clays and compacted subgrade soils. At small strains below the elastic threshold, shear modulus is independent of number of loading cycles and strain amplitude. Small strain material damping exists wi th ranges be tween 1.1% and 1.7% for 75 tests. The elastic threshold strain increases as confining pressure and plasticity index increases. Above the cyclic threshold strain, the modulus of cohesive soil decreases with increasing number of cycles while damping ratio is almost independent of number of load cycles. Moduli and damping ratios of cohesive soils obtanined by RC test are higher than those from 75 test because of the frequency effect. Shear modulus of cohesive soil increases linearly as a function of the logarithm of loading frequency.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.40-40
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• 2003

최근 나노기술의 발달과 더불어 나노재료에 대한 특성평가 요구가 높아지고 있고, 따라서 나노스케일에서 재료의 기계적 거동을 분석할 수 있는 나노인덴테이션 기법이 심도있게 연구되고 있다. 본 연구에서는 나노인덴테이션, 주사탐침현미경(SPM), 투과전자현미경(TEM) 기법을 이용하여 여러가지 재료의 탄성 소성 변형 거동과 팝인/괍아웃 현상을 조사하고 해석하였다. 나노인덴테이션 기법으로는 50 마이크로뉴턴 (5 mg) 이하의 매우 작은 하중 하에서는 접촉 응력조건이라도 인장시험에서 관찰되는 영구변형이 제로인 완전탄성 변형 거동을 관찰할 수 있었다. 또한, 50-250 마이크로 뉴턴의 하중 범위에서 재료는 탄성변형 이후에 갑작스런 항복거동과 더불어 수십-수백 나노미터를 미끌어지듯 변형하는 팝인(pop-in), 또는 탈선(excursion) 현상을 관찰할 수 있었다. 이 현상은 하중을 가하는 동안에 여러 번 발생하였으며 재료의 표면상태와 전위밀도와 밀접한 상관관계를 보였다. 반복 압입 시험에서는 전형적인 가공경화 현상으로 항복점이 높아지고 새로운 항복점 이후에야 다시 팝인 발생함을 보였다. 한편, 하중을 가할 때 발생하는 팝인과는 달리 하중을 제거할 때 급격히 회복하는 팝아웃 현상 또한 관찰되었다.

• Journal of Korean Society of Steel Construction
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• v.23 no.3
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• pp.305-316
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• 2011

As the building structures are higher and bigger, the high-performance steels of high strength, toughness, and low yield ratio had been required and developed. In this paper the behavior of the moment connection with bolted web and high strength steel was studied by using the finite-element analysis computer program of ABAQUS. The analysis model is based on the test results and the same cyclic load history was applied at the FE(Finite Element) model until it failed in the test. Through the FEA, several indicators hardly measured from the test were acquired. These indicators related to stress and strain were selected from three plastic rotation stages: 0.003 rad, 0.03 rad, and final failure rotation. Specifically, at the final failure stage, the strain indicators producing the full plastic behavior were suggested as a mechanical property for steel.