• Journal of the Korean Society of Safety
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• v.17 no.4
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• pp.52-60
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• 2002

Failure criterion is a parameter to represent the resistance to failure of locally wall thinned pipe, and it depends on material characteristics, defect geometry, applied loading type, and failure mode. Therefore, accurate prediction of integrity of wall thinned pipe requires a failure criterion adequately reflected the characteristics of defect shape and loading in the piping system. In the present study, the finite element analysis was performed and the results were compared with those of pipe experiment to develop a sound criterion for failure of internally wall thinned pipe subjected to combined pressure and bending loads. By comparing the predictions of failure to actual failure load and displacement, an appropriate criterion was investigated. From this investigation, it is concluded that true ultimate stress criterion is the most accurate to predict failure of wall thinned pipe under combined loads, but it is not conservative under some conditions. Engineering ultimate stress estimates the failure load and displacement reasonably for al conditions, although the predictions are less accurate compared with the results predicted by true ultimate stress criterion.

• Steel and Composite Structures
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• v.38 no.6
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• pp.617-635
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• 2021

This paper numerically investigated the behavior of built-up square concrete-filled steel tubular (CFST) columns under combined preload and axial compression. The finite element (FE) models of target columns were verified in terms of failure mode, axial load-deformation curve and ultimate strength. A full-range analysis on the axial load-deformation response as well as the interaction behavior was conducted to reveal the composite mechanism. The parametric study was performed to investigate the influences of material strengths and geometric sizes. Subsequently, influence of construction preload on the full-range behavior and confinement effect was investigated. Numerical results indicate that the axial load-deformation curve can be divided into four working stages where the contact pressure of curling rib arc gradually disappears as the steel tube buckles; increasing width-to-thickness (B/t) ratio can enhance the strength enhancement index (e.g., an increment of 1.88% from B/t=40 to B/t=100), though ultimate strength and ductility are decreased; stiffener length and lip inclination angle display a slight influence on strength enhancement index and ductility; construction preload can degrade the plastic deformation capacity and postpone the origin appearance of contact pressure, thus making a decrease of 14.81%~27.23% in ductility. Finally, a revised equation for determining strain εscy corresponding to ultimate strength was proposed to evaluate the plastic deformation capacity of built-up square CFST columns.

• Structural Monitoring and Maintenance
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• v.8 no.4
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• pp.345-360
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• 2021

This paper presents an analytical approach to calculate the buckling load of the cylindrical ring structures subjected to both hydrostatic and hydrodynamic pressures. Based on the conservative law of energy and Timoshenko beam theory, a theoretical formula, which can be used to evaluate the critical pressure of buckling, is first derived for the simplified cylindrical ring structures. It is assumed that the hydrodynamic pressure can be treated as an equivalent hydrostatic pressure as a cosine function along the perimeter while the thickness ratio is limited to 0.2. Note that this paper limits the deformed shape of the cylindrical ring structures to an elliptical shape. The proposed analytical solutions are then compared with the numerical simulations. The critical pressure is evaluated in this study considering two possible failure modes: ultimate failure and buckling failure. The results show that the proposed analytical solutions can correctly predict the critical pressure for both failure modes. However, it is not recommended to be used when the hydrostatic pressure is low or medium (less than 80% of the critical pressure) as the analytical solutions underestimate the critical pressure especially when the ultimate failure mode occurs. This implies that the proposed solutions can still be used properly when the subsea vehicles are located in the deep parts of the ocean where the hydrostatic pressure is high. The finding will further help improve the geometric design of subsea vehicles against both hydrostatic and hydrodynamic pressures to enhance its strength and stability when it moves underwater. It will also help to control the speed of the subsea vehicles especially they move close to the sea bottom to prevent a catastrophic failure.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.15-22
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• 2016

The magnitude of the lateral resistance that resists the lateral movement of the pile is controlled by the amount of the pile movement and the strength and stiffness of soil. In this paper, we proposed an equation which produces the ultimate lateral resistance of the laterally loaded single pile in sand using the strain wedge model of the soil deformation. The ultimate lateral resistance in strain wedge model is composed of earth pressure of wedge rear, the shear resistance on the side of the wedge, and the frictional resistance between pile and ground. The ultimate lateral resistance determined by the proposed equation was compared with the Ashour, F.D.M., field test in sand. As a result, the error of the proposed equation and Ashour theory, field test, F.D.M were respectively 1.03%, 0.40~3.32%, 6.02%.

• Geotechnical Engineering
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• v.14 no.5
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• pp.143-162
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• 1998

In the present study, a procedure to predict the depth from the ground surface to the center of bulging failure zone in each of the square granular group piles under a rigid mat foundation is proposed. This analytical procedure is established on the basis of the conical modeling of bulging failure shape and the replacement ratio of soft foundation soils. considering the effect of a share of procedure to estimate the ultimate cylindrical pressure in the area reinforced with granular piles and the ultimate bearing capacity of each of granular piles in group. This analytical procedure is also established on the basis of the pre-determined depth to the zone of bulging failure and an iterative solution technique. Finally the analytical procedures proposed in this study are verified by analyzing the results of 3D finite element analyses, and the predictions of ultimate bearing capacity of granular piles are compared with the results obtained from the tests, empirical equation and 3D finite element analyses.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.183-189
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• 2005

Nuclear containment structure is the last barrier for being secure from any nuclear power plant accident. Even though the safety requirements of nuclear power plant have been focused on removing accidental situations, nuclear containment structure must reserve the sufficient resisting capacity to any accident because it works as the last barrier. The acceptable nuclear containment structure makes possible to limit the effect of internal accidents and to avoid radioactive release. In this study, to conduct the numerical analysis for the structural safety of a containment structure, loss of coolant accident (LOCA) is considered as the basic accidental load, and Wolsong containment structure is considered as a target structure. The CANDU containment structure, such as Wolsong containment structure, is a prestressed concrete shell structure which has dome and is reinforced with bonded tendons. The evaluation of ultimate pressure capacity was conducted by nonlinear analysis of a prestressed concrete containment structure.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.577-580
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• 2002

In this paper, the pumping performance of the disk-type drag pump which works in the outlet pressure range from 4 to 0.001 Torr is studied experimentally. The pumping characteristics of various drag pumps are performed. The inlet pressures are measured for various outlet pressures of the test pump. The flow-meter method is adopted to calculate the pumping speed. Compression ratios and pumping speeds for the nitrogen gas are measured. The present experimental data show the leak-limited value of the compression ratio in the molecular transition region. The rotational speed of the pump is 24,000rpm. The inlet pressures are measured for various outlet pressures of the test pump. The ultimate Pressures for zero throughput are measured for three-stage, two-stage and single-stage disk-type, respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.299-306
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• 2001

Crushed Stone Pile(CSP) is one of the ground improvement methods available to loose sand and clayey ground by forming compacted CSP in the weak soil layer. The effects of this method are enhancement of ground bearing capacity, reduction of settlement and prevention of lateral ground movement in cohesive layer, reduction of liquefaction potential in sandy ground. This study performs model tests in 1.0m${\times}$1.0m${\times}$1.0m and 1.5m${\times}$1.5m${\times}$l.2m model tank to observe bearing capacity of CSP treated ground. The area replacement ratio of CSP composite ground varies 20%, 30% and 40% with square grid pattern. After the composite ground was consolidated under pressure of 0.5kg/$\textrm{cm}^2$ and 1.0kg/$\textrm{cm}^2$, load tests were carried out. The results show that ultimate bearing capacity increases with area replacement ratio and the preconsolidation pressure of ground.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.419-419
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• 1999

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.335-335
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• 2010

한국표준과학연구원 진공센터에서는 국제규격에 바탕을 둔 저진공펌프 종합특성평가시스템을 구축하여 $1100mbar\;{\sim}\;10^{-3}mbar$ 압력 영역에서의 저진공펌프(roots, dry 등)류의 종합특성평가를 시행하고 있다. 저진공펌프 종합특성평가시스템은 국제적 절차에 따른 신뢰성을 바탕으로 구축하고 있으나, 한국표준과학연구원 진공센터 뿐만 아니라, 국내에서도 고진공 종합특성평가 시스템을 구축 하고 있지 않다. 이에 반도체/디스플레이 등 첨단 공정에서 진공 환경을 조성하는 핵심장비인 고진공펌프의 종합특성평가시스템을 개발하고자 터보펌프(TMP) 1000L/s 급의 database를 구축 하였다. 터보펌프(TMP)는 throughput method와 orifice method 두 가지 방법을 병행하여 pumping speed 측정한다. orifice method는 일종의 미세유량 측정 장치이며, 실험값과 계산값 유량의 오차 범위가 작고 신뢰성을 확보하면 throughput method 만으로 측정할 수 있다. Througput method는 $10^{-6}mbar$ 압력 이상의 영역을 측정하며, ultimate pressure 및 $150^{\circ}C$의 bake-out 을 진행하여 base pressure을 측정 할 수 있으며, $10^{-6}mbar$ 압력 이상의 pumping speed를 측정 할 수 있다. 이에 따른 정압형 유량시스템을 개발 중에 있으며, inlet pressure와 outlet pressure를 이용한 compression ratio를 측정 한다. Orifice method는 ultimate pressure와 base pressure을 측정하며, leak valve를 이용한 컨덕턴스(C)로 pressure ratio을 이용하여 유량값을 계산하며, $10^{-6}mbar$ 압력 이하의 pumping speed를 측정할 수 있다. 또한 throughput method와 orifice method의 pumping speed 뿐만 아니라 소비전력 및 소음, 진동, 온도 등 특성평가 관련 사항들의 전반적인 사항을 평가하여 터보펌프(TMP) 1000L/s 급의 database를 구축한다. 향후 예비 실험을 통한 고진공펌프의 종합특성평가시스템을 완비해 나가며, 고진공펌프 종합 특성평가시스템을 통하여 국제적으로 공인받을 수 있는 평가기준을 확립하고 그 기준에 의한 진공/기계적 성능의 전방위적인 종합특성진단과 공정대응성 평가 등 국제적 기술 신뢰성을 확보하고자 한다.