• Steel and Composite Structures
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• 제26권4호
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• pp.439-452
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• 2018

This paper presents experimental and numerical study on buckling behaviors and hysteretic performance of Class 1 H-shaped steel beam subjected to cyclic pure bending within the scope of ultra-low cycle fatigue (ULCF). A loading device was designed to achieve the pure bending loading condition and 4 H-shaped specimens with a small width-to-thickness ratio were tested under 4 different loading histories. The emphasis of this work is on the impacts induced by local buckling and subsequent ductile fracture. The experimental and numerical results indicate that the specimen failure is mainly induced by elasto-plastic local buckling, and is closely correlated with the plastic straining history. Compared with monotonic loading, the elasto-plastic local buckling can occur at a much smaller displacement amplitude due to a number of preceding plastic reversals with relative small strain amplitudes, which is mainly correlated with decreasing tangent modulus of the material under cyclic straining. Ductile fracture is found to be a secondary factor leading to deterioration of the load-carrying capacity. In addition, a new ULCF life evaluation method is proposed for the specimens using the concept of energy decomposition, where the cumulative plastic energy is classified into two categories as isotropic hardening and kinematic hardening correlated. A linear correlation between the two energies is found and formulated, which compares well with the experimental results.

• Earthquakes and Structures
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• 제11권4호
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• pp.649-664
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• 2016

A seismic damaged bridge may be hit again by a strong aftershock or another earthquake in a short interval before the repair work has been done. However, discussions about the impact of the unrepaired damages on the residual earthquake resistance of a steel bridge are very scarce at present. In this paper, nonlinear time-history analysis of a steel arch bridge was performed using multi-scale hybrid model. Two strong historical records of main shock-aftershock sequences were taken as the input ground motions during the dynamic analysis. The strain response, local deformation and the accumulation of plasticity of the bridge with and without unrepaired seismic damage were compared. Moreover, the effect of earthquake sequence on crack initiation caused by low-cycle fatigue of the steel bridge was investigated. The results show that seismic damage has little impact on the overall structural displacement response during the aftershock. The residual local deformation, strain response and the cumulative equivalent plastic strain are affected to some extent by the unrepaired damage. Low-cycle fatigue of the steel arch bridge is not induced by the earthquake sequences. Damage indexes of low-cycle fatigue predicted based on different theories are not exactly the same.

• Earthquakes and Structures
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• 제19권3호
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• pp.189-196
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• 2020

The near-collapse performance limit is defined as the deformation at the 20% drop of maximum base shear in the decreasing region of the pushover curve for ductile framed buildings. Although monotonic pushover analysis is preferred due to the simple application procedure, this analysis gives rise to overestimated results by neglecting the cumulative damage effects. In the present study, the acceptabilities of monotonic and cyclic pushover analysis results for the near-collapse performance limit state are determined by comparing with Incremental Dynamic Analysis (IDA) results for a 5-story Reinforced Concrete framed building. IDA is performed to obtain the collapse point, and the near-collapse drift ratios for monotonic and cyclic pushover analysis methods are obtained separately. These two alternative drift ratios are compared with the collapse drift ratio. The correlations of the maximum tensile and compression strain at the base columns and beam plastic rotations with interstory drift ratios are acquired using the nonlinear time history analysis results by the simple linear regression analyses. It is seen that these parameters are highly correlated with the interstory drift ratios, and the results reveal that the near-collapse point acquired by monotonic pushover analysis causes unacceptably high tensile and compression strains at the base columns, as well as large plastic rotations at the beams. However, it is shown that the results of cyclic pushover analysis are acceptable for the near-collapse performance limit state.

• Steel and Composite Structures
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• 제24권4호
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• pp.441-453
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• 2017

In Y-shaped eccentrically braced frame fabricated with high strength steel (Y-HSS-EBF), link uses conventional steel while other structural members use high strength steel. Cyclic test for a 1:2 length scaled one-bay and one-story Y-HSS-EBF specimen and shake table test for a 1:2 length scaled three-story Y-HSS-EBF specimen were carried out to research the seismic performance of Y-HSS-EBF. These include the failure mode, load-bearing capacity, ductility, energy dissipation capacity, dynamic properties, acceleration responses, displacement responses, and dynamic strain responses. The test results indicated that the one-bay and one-story Y-HSS-EBF specimen had good load-bearing capacity and ductility capacity. The three-story specimen cumulative structural damage and deformation increased, while its stiffness decreased. There was no plastic deformation observed in the braces, beams, or columns in the three-story Y-HSS-EBF specimen, and there was no danger of collapse during the seismic loads. The designed shear link dissipated the energy via shear deformation during the seismic loads. When the specimen was fractured, the maximum link plastic rotation angle was higher than 0.08 rad for the shear link in AISC341-10. The Y-HSS-EBF is a safe dual system with reliable hysteretic behaviors and seismic performance.

• Structural Engineering and Mechanics
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• 제59권1호
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• pp.37-57
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• 2016

Reservoir geomechanics can play an important role in hydrocarbon recovery mechanism. In $CO_2$-EOR process, reservoir geomechanics analysis is concerned with the simultaneous study of fluid flow and the mechanical response of the reservoir under $CO_2$ injection. Accurate prediction of geomechanical effects during $CO_2$ injection will assist in modeling the Carbon dioxide recovery process and making a better design of process and production equipment. This paper deals with the implementation of a program (FORTRAN 90 interface code), which was developed to couple conventional reservoir (ECLIPSE) and geomechanical (ABAQUS) simulators, using a partial coupling algorithm. A geomechanics reservoir partially coupled approach is presented that allows to iteratively take the impact of geomechanics into account in the fluid flow calculations and therefore performs a better prediction of the process. The proposed approach is illustrated on a realistic field case. The reservoir geomechanics coupled models show that in the case of lower maximum bottom hole injection pressure, the cumulative oil production is more than other scenarios. Moreover at the high injection pressures, the production rates will not change with the injection bottom hole pressure variations. Also the FEM analysis of the reservoir showed that at $CO_2$ injection pressure of 11000 Psi the plastic strain has been occurred in the some parts of the reservoir and the related stress path show a critical behavior.

• 한국철도학회논문집
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• 제18권3호
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• pp.241-251
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• 2015

유도상 아스팔트 콘크리트 궤도(이하, 유도상 AC궤도)는 아스팔트 콘크리트 노반(이하, AC노반)의 존재에 의해 유도상 궤도에 비해 열차하중 분산효과에 의한 강화노반 두께 감소가 가능하며 누적 소성 변위도 작을 뿐만 아니라 유지관리 측면에서도 유리한 궤도 구조이기 때문에 국외에서 적용 사례가 증가하고 있다. 그러므로 유도상 AC궤도의 국내 도입을 검토하기 위해 선행 연구를 통해 수행한 AC노반 유무에 따른 거동 특성을 분석하여 현재 설계기준에 명시된 유도상 궤도의 단면과 유사한 성능을 보이는 유도상 AC궤도의 단면을 분석한 바 있으며, 실대형 정 동적 열차하중 재하 실험 결과와의 비교를 통해 해석 결과의 신뢰성을 검증하였다. 본 연구에서는 선행 연구를 바탕으로 AC노반의 두께를 일정하게 하고 강화노반 두께를 변화시켰을 때에 획득된 AC노반 하면에서의 변형률을 이용하여 설계 수명을 산정하였고 각각의 단면에 대한 확률론적 LCC분석을 통해 기대 설계 수명을 만족하면서 기존 유도상 궤도와 비교하여 동등 또는 동등이상의 성능을 갖는 유도상 AC궤도의 설계 단면을 제시하였다.

• 한국가스학회지
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• 제3권3호
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• pp.1-8
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• 1999

Membrane용 오스테나이트계 304 스테인리스강 판재의 3점 굽힘피로 특성에 관한 연구를 상온 및 LNG 온도인 $-162^{\circ}C$, 변형량 $0.43{\~}1.70\%$ 범위에서 수행하였다. 저온에서의 굽힘피로 특성이 상온보다 우수한 것으로 나타났고, 이는 변형유기 마르텐사이트 변태에 필요한 구동력이 적어서 보다 많은 양의 마르텐사이트를 함유했기 때문으로 판단된다. 상온 및 저온 모두에서 반복경화 현상이 관찰되었으며, 이러한 반복경화는 상온의 경우 피로주기가 반복됨에 따라 점진적으로 증가되지만 저온의 경우 초기 피로주기에서 급격히 증가된 후 점차로 감소하거나 일정한 값을 나타내었는데 이러한 차이는 저온의 경우 초기에 급격히 변형유기 마르텐사이트가 생성되지만 상온의 경우 변형유기 마르텐사이트 생성에는 일정한 소성변형의 축적이 필요하기 때문으로 생각된다. 기존의 JGA 연구결과와 비교해 볼 때 본 연구에서 사용된 국산소재의 굽힘피로 특성이 우수한 것으로 나타났다.

• Journal of Welding and Joining
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• 제17권1호
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• pp.124-132
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• 1999

Thermal fatigue strength of the solder joints is the most critical issue for TSOP(Thin Small Outline Package) because the leads of this package are extremely short and thermal deformation cannot be absorbed by the deflection of the lead. And the TSOP body can be subject to early fatigue failures in thermal cycle environments. This paper was discussed distribution of thermal stresses at near the joint between silicon chip and die pad and investigated their reliability of solder joints of TSOP with 42 alloy clad lead frame on printed circuit board through FEM and 3 different thermal cycling tests. It has been found that the stress concentration around the encapsulated edge structure for internal crack between the silicon chip and Cu alloy die pad. And using 42 alloy clad, The reliability of TSOP body was improved. In case of using 42 alloy clad die pad(t=0.03mm). $$\sigma$_{VMmax}$ is 69Mpa. It is showed that 15% improvement of the strength in the TSOP body in comparison with using Cu alloy die pad $($\sigma$_{VMmax}$=81MPa). In solder joint of TSOP, the maximum equivalent plastic strain and Von Mises stress concentrate on the heel of solder fillet and crack was initiated in it's region and propagated through the interface between lead and solder. Finally, the modified Manson-Coffin equation and relationship of the ratio of $N_{f}$ to nest(η) and cumulative fracture probability(f) with respect to the deviations of the 50% fracture probability life $(N_{f 50%})$ were achieved.