• 대한토목학회논문집
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• 제31권2A호
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• pp.71-77
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• 2011

본 논문은 고체의 동적 탄소성해석을 수행하기 위해 인장불안정이 제거된 SPH기법을 사용하였다. 인장불안정은 SPH 입자들이 인장력에 의해 서로 떨어져나가는 해석적 오류현상이며, 재료적 특성에 따라 해석결과에 큰 영향을 미치게 된다. 이와 같은 인장불안정을 제어하기 위한 방법으로 본 연구에서는 가상응력의 개념을 적용하였다. 본 연구에서 제시한 SPH에 의해 해석예제를 수행하여 해석법의 효율성을 검증하였으며, 해석예제로 원형 링의 충돌문제와, 절단, 균열과 같은 재료적 파괴문제를 수행하였다.

• Structural Engineering and Mechanics
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• 제14권4호
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• pp.455-472
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• 2002

The paper involves the study on the elastic and elasto-plastic stress wave propagation in the 1-D and 2-D solid media. The Smooth Particle Hydrodynamics equations governing the elastic and elasto-plastic large deformation dynamic response of solid structures are presented. The proposed additional stress points are introduced in the formulation to mitigate the tensile instability inherent in the SPH approach. Both incremental rate approach and leap-frog algorithm for time integration are introduced and the new solution algorithm is developed and implemented. Two examples on stress wave propagation in aluminium bar and 2-D elasto-plastic steel plate are included. Results from the proposed SPH approach are compared with available analytical values and finite element solutions. The comparison illustrates that the stress wave propagation problems can be effectively solved by the proposed SPH method. The study shows that the SPH simulation is a reliable and robust tool and can be used with confidence to treat transient dynamics such as linear and non-linear transient stress wave propagation problems.

• 한국농공학회지
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• 제44권3호
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• pp.92-100
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• 2002

The advent or high-strength steel has enabled the arch structures to be relatively light, durable and long-spanned by reducing the cross sectional area. On the other hand, the possibility of collapse may be increased due to the slender members which may cause the stability problems. The limit analysis to estimate the ultimate load is based on the concept of collapse mechanism that forms the plastic zone through the full transverse sections. So, it is not appropriate to apply it directly to the instability analysis of arch structures that are composed with compressive members. The objective of this study is to evaluate the ultimate load carrying capacity of the parabolic arch by using the elasto-plastic finite element model. As the rise to span ratio (h/L) varies from 0.0 to 0.5 with the increment of 0.05, the ultimate load has been calculated fur arch structures subjected to uniformly distributed vertical loads. Also, the disco-elasto-plastic analysis has been carried out to find the duration time until the behavior of arch begins to show the stable state when the estimated ultimate load is applied. It may be noted that the maximum ultimate lead of the parabolic arch occurs at h/L=0.2, and the appropriate ratio can be recommended between 0.2 and 0.3. Moreover, it is shown that the circular arch may be more suitable when the h/L ratio is less than 0.2, however, the parabolic arch can be suggested when the h/L ratio is greater than 0.3. The ultimate load carrying capacity of parabolic arch can be estimated by the well-known formula of kEI/L$^3$where the values of k have been reported in this study. In addition, there is no general tendency to obtain the duration time of arch structures subjected to the ultimate load in order to reach the steady state. Merely, it is observed that the duration time is the shortest when the h/L ratio is 0.1, and the longest when the h/L ratio is 0.2.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.85-87
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• 2012

We present a numerical investigation on gaseous (ethylene-air mixture) detonation in the elastoplastical metal tubes to understand the wall effects associated with the developing detonation instability. The acoustic disturbances originating from the rapidly expanding tube walls reach the detonating flame surface, thereby causing flame distortions and total energy losses. The compressible Navier-Stokes equations with equation of state for gas and elasto-plastic deformation field equations for inert tubes are solved simultaneously to understand the complex multi-material interaction in the rapidly expanding gas pipe. In order to track governing variables across the material interface, we use the hybrid particle level-set and ghost fluid methods to precisely estimate the interfacial quantities. Features observed from the deforming (thin) tube show substantially different behavior when a detonation propagates in the rigid (thick) tube with no acoustically responding wall conditions.

• Steel and Composite Structures
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• 제12권4호
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• pp.291-302
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• 2012

Frequently, steel silos are supported by discrete supports or columns to permit easy access beneath the barrel. In such cases, large loads are transferred to the limited number of supports, causing locally high axial compressive stress concentrations in the shell wall above the supports. If not dealt with properly, these increased stresses will lead to premature failure of the silo due to local instability in the regions above the supports. Local stiffening near the supports is a way to improve the buckling resistance, as material is added in the region of elevated stresses, levelling these out to values found in uniformly supported silos. The aim of a study on the properties of local stiffening will then be to increase the failure load, governed by an interaction of plastic collapse and elastic instability, to that of a discrete supported silo. However, during the course of such a study it was found that, although the failure remains local, the cylinder height is also a parameter that influences the failure mechanism, a fact that is not properly taken into account in current design practice and codes. This paper describes the mechanism behind the effect of the cylinder height on the failure load, which is related to pre-buckling deformations of the shell structure. All results and conclusions are based on geometrically and materially non-linear finite element analyses.

• Structural Engineering and Mechanics
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• 제2권2호
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• pp.185-196
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• 1994

In this paper a spline function solution for the ultimate strength of steel members and member structures is derived based on total Lagrangian formulation. The displacements of members along longitudinal and transverse directions are interpolated by one-order B spline functions and three-order hybrid spline functions respectively. Equilibrium equations are established according to the principle of virtual work. All initial imperfections of members and effects of loading, unloading and reloading of material are taken into account. The influence of the instability of members on structural behavior can be included in analyses. Numerical examples show that the method of this paper can satisfactorily analyze the elasto-plastic large deflection problems of planar steel member and member structures.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1346-1351
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• 2003

There is few research about contact problem in SPH because it is primarily suitable to analyze the large deformation problem. However, an elasto-plastic problem with small deformation need to be considered about contact characteristics. The numerical formulating methods for SPH is induced to be able to obtain solutions based on a variational method in contact problem. The contact algorithm presented is applied to the elastic impact problem in 1D and 2D. The results show thai an imaginary tension and a numerical instability which happen in impacting between different materials can be removed and contact forces which could not have been calculated are able to obtain.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.269-273
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• 2003

During the laser welding, weldments are suddenly heated by laser beam and cooled. This phenomenon gives occasion to complex welding residual stresses, which have a great influence on structural instability strength, in laser welds. However, a relevant research on this field is not sufficient until present and residual stress measurements have experimental and practical limitations. For these reasons a numerical simulation may be attractive in order to solve the residual stress problem. In order to determine the distribution of heat and welding residual stresses in laser welds with the nail-head shape, authors conduct the finite element analysis (two-dimensional unstationary heat conduction & thermal elasto-plastic analysis). From the result of this study, we can confirm the stress concentration is occurred at the place of melting line shape changed in laser welds with the nail-head shape.

• Structural Engineering and Mechanics
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• 제91권4호
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• pp.369-382
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• 2024

The earthquake loss assessment framework of ductile reinforced concrete (or RC) frame using component-performance -based methodology was studied in this paper. The elasto-plastic rotation angle was used as the damage indicator of structural component, and the damage-to-loss model was proposed on the basis of the deformation indicator of structural component. Dynamic instability during incremental dynamic analysis was taken as collapse criterion, and column failure was taken as criterion that structure has to be demolished. Expected earthquake losses of low-rise, mid-rise and high-rise RC frames were discussed. The expected earthquake loss encompassed collapse loss, demolition loss and repair loss. Furthermore, component groups of RC frame were divided into structural components, nonstructural components and rugged components. The results indicate that ductile RC frame is more likely to be demolished than collapse, especially in low-rise and mid-rise RC frames. Furthermore, the less collapse margin ratio the structure has, the more demolition probability the structure will suffer under rare earthquake. The demolition share of total earthquake loss might be more prominent than repair share and collapse share in ductile RC frame.

• 한국구조물진단유지관리공학회 논문집
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• 제21권3호
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• pp.102-113
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• 2017

비정형 판 부재의 탄소성 좌굴 강도를 평가할 수 있는 새로운 지표를 제안하였다. 부재 경계면에 작용하는 하중 또는 경계면의 변화에 따른 외부일 또는 변형에너지를 부재의 평형 변형경로에 따라 계산하고, 이 에너지의 이차 변분량의 부호가 양에서 음으로 바뀌는 시점을 안정한계로 제안하였다. 판 부재의 단면력을 등분포 또는 선형으로 근사한 상태로 단면력을 사용하여 좌굴한계를 평가하는 현 기법과는 반대로 단면력의 변화가 비선형적인 복잡한 경우에도 간단히 좌굴한계를 평가할 수 있다. 선형탄성 문제에 대해서는 본 기법의 결과와 전통적인 방법이 동일한 결과를 도출한다.