• 한국농공학회지
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• 제41권4호
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• pp.77-85
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• 1999

In this study, a computer program considering initial imperfection of axisymmetric reinforced concrete shell which plastic deformation by large external loading was developed . Initial imperfection of dome was assumed as 'dimple type' which can be expressed as Wi=(Wo/h)(1-x$^2$)$^3$. The developed model applied to the analysis of dynamic response of axisymmetric reinforced concrete shell when it has initial imperfection. The initial imperfection of 0.0, -5.0, and 5cm and steel and steel layer ratio 0,3, and 5% were tested for numerical examples . The results can be summarized as follows ; 1. Dynmaic response of vertical deflection at dome crown showed slow increased if it has not inital imperfection . But the response showed relatively high amplitude when initial imperfection was inner directed (opposite direction to loading). Similar trends also appeared for different steel layer ratios. 2. Dynamic responses of radial displacement at the junction of dome and wall showed the highest amplitude when initial imperfection was inward directed (opposite direction to loading). The lowest amplitude occurred when initial imperfection was outward directed (same direction to loading). Vibration period also delayed for inward directed initial imperfection . These trends were obvious as steel layer ratio increasing. 3. The effects of imperfection for the dynamic response of radial displacement a the center of wall scarely appeared. The effects of initial imperfection of dome on the dynmaic response of the wall can be neglected. 4. Effect of steel on the dynmic response of axisymmetric shell structure was great when initial imperfection did not exist. And the effect of direction of initial imperfection (inward or outward) did not show big difference.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 가을 학술발표회 논문집
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• pp.55-60
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• 1994

The paper is aimed at investigating the buckling strength of single-layer latticed domes with the geometrically initial imperfection under the uniformly distributed vertical-loading and the partially concentrated equipment-loading. The results show that the effect of initial imperfection on the buckling strength, if the magnitude of equipment-loading is small, is much more sensitive in domes of overall buckling than in domes of member buckling, but with increasing equipment-loading, it is very sensitive both in domes of overall buckling and of member buckling

• 한국농공학회지
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• 제42권5호
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• pp.151-159
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• 2000

Dynamic loading of structures often causes excursions of stresses will into the inelastic range and the influence of geometry changes on the response is also significant in may cases. In general , the shell structures designed according to quasi-Static analysis may collapse under condition of dynamic loading. Therefore, for a more realistic prediction on the lad carrying capacity of these shell. both material and geometric nonlinear effects should be considered. In this study , the material nonlinearity effect on the dynamic response is formulated by the elasto-viscoplastic model highly corresponding to the real behavior of the material. Also, the geometrically nonlinear behavior is taken into account using a Total Lagrangian formulation. the reinforcing bars are modeled by the equivalent steel layer at the location of reinforcements, and Von Mises yield criteria is adopted for the steel layer behavior. Also, Drucker-Prager yield criteria is applied for the behavior of concrete. the shape imperfection of dome is assumed as 'dimple type' which can be expressed Wd1=Wd0(1-(r-a)m)n while the shape imperfection of wall is assumed as sinusoidal curve which is Wwi =Wwo sin(n $\pi$y/l). In numerical test, three cases of shape imperfection of 0.0 -5.0cm(opposite direction to loading ; inner shape imperfection)and 5cm (direction to loading : outward shape imperfection) and thickness of steel layer determined by steel ratio of 0,3, and 5% were analyzed. The effect of shape imperfection and steel ratio and behavior characteristics of perfect shape shell and imperfect shape shell are identified through analysis of above mentioned numerical test. Dynamic behaviors of dome and wall according toe combination of shape imperfection and steel ratio are also discussed in this paper.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1999년도 Proceedings of the 1999 Annual Conference The Korean Society of Agricutural Engineers
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• pp.200-205
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• 1999

In this study, a computer program considering iniial imperfectiionof axiymmetric reinforced concrete shell which show plastic deformation by large external loading was developed . Initial imperfection of wall was assumed as 'sine curve' which can be expressed as Wi =W0 sin(n$\pi$/1y). The developed model was applied to the analysis of dynamic response of axisymmetric reinforced concrete shell when it has initial imperfection . The initial imperfection of 0.0, -5.0 and 5 cm and steel ration 0 , 3 and 5% were tested for numerical examples.

• Advances in materials Research
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• 제8권3호
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• pp.219-235
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• 2019

This research is devoted to analyzing mechanical-thermal post-buckling behavior of a micro-size beam reinforced with graphene platelets (GPLs) based on geometric imperfection effects. Graphene platelets have three types of dispersion within the structure including uniform-type, linear-type and nonlinear-type. The micro-size beam is considered to be perfect (ideal) or imperfect. Buckling mode shape of the micro-size beam has been assumed as geometric imperfection. Modified couple stress theory has been used for describing scale-dependent character of the beam having micro dimension. Via an analytical procedure, post-buckling path of the micro-size beam has been derived. It will be demonstrated that nonlinear buckling characteristics of the micro-size beam are dependent on geometric imperfection amplitude, thermal loading, graphene distribution and couple stress effects.

• 한국농공학회지
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• 제42권3호
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• pp.114-120
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• 2000

In this study a computer program considering initial imperfection of wall of axisymmetric reinforced concrete shell which show plastic deformation by large external loading is developed. initial imperfection of wall of axisymmetric reinforced concrete shell is assumed as sinusoidal curve expressed as {{{{ {W }_{i } }}}}={{{{ {W}_{0 } }}}}sin (n$\pi$y/$\ell$)y. The developed program is applied to the analysis of the dynamic response of axisymmetric reinforced concrete shell when the wall has initial imperfection. The initial imperfection of 0.0 -5.0, and 5cm and steel ratio 0.3, and 5% are tested for numerical examples. The effects of the wall initial imperfection and steel ratio on the dynamic response of the axisymmetric reinforced concrete shell are analysed, It is shown that the direction of the initial imperfection is very important factors for determining the dynamic response.

• 한국자동차공학회논문집
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• 제1권2호
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• pp.42-48
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• 1993

In this paper, dynamic collapse behavior of the rectangular tube under impact loading is anlayzed using nonlinear finite element method of shell element. In case of shell element formulation using corotational element coordinates system, dynamic collapse behavior is analyzed without initial imperfection, and with initial imperfection. This paper reveals that the collapse of a rectangular tue without initial imperfection is caused by an error of transformation of the corotational coordinates system.

• Composites Research
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• 제34권5호
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• pp.283-289
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• 2021

본 연구에서는 압축력을 받는 얇은 복합재 원통 구조에 대하여 기하학적 혹은 하중에 대한 초기 결함 모델을 이용하여 수치해석적으로 좌굴 Knockdown factor를 새롭게 도출하였다. 전역 좌굴이 발생하기 이전에 타원형상의 변형 형상을 갖는 복합재 원통 구조를 사용하였다. 복합재 원통 구조의 기하학적 초기 결함만 고려하기 위하여 Single Perturbation Load Approach를 이용하였으며, 기하학적 초기 결함과 더불어 하중 불균일을 함께 구현하기 위하여 Single Boundary Perturbation Approach를 사용하였다. 기하학적 초기 결함 모델의 좌굴 Knockdown factor는 NASA의 기존의 좌굴 Knockdown factor보다 약 84% 높게 도출되었으며, 좌굴 시험에 비하여서는 약 9% 낮게 도출되었다. 기하학적 초기 결함과 하중 불균일을 함께 고려하는 모델의 좌굴 Knockdown factor는 NASA의 좌굴 Knockdown factor에 비하여서는 약 75% 높게, 그리고 좌굴 시험보다 약 14% 낮게 계산되었다. 따라서, 본 연구의 좌굴 설계 기준은 고려된 초기 결함 모델과 상관없이 기존의 좌굴 설계 기준에 비하여 경량 설계의 제공이 가능함과 동시에 좌굴 시험 대비 적절히 보수적인 설계 기준을 제공할 수 있음을 확인하였다.

• 한국강구조학회 논문집
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• 제9권3호통권32호
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• pp.323-332
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• 1997

구형 단층래스티돔은 강성이 강한 반면 외력이 어느 임계치에 도달하면 좌굴에 의해 구조물 전체의 붕괴가 발생할 수 있다. 특히 시공오차에 의해 발생할 수 있는 기하학적 형상부정과 설비시설 등에 의한 집중하중은 구조물의 내력을 감소시키는 주 요인이 될 수 있다. 본 연구에서는 기하학적으로 형상 부정이 없는 완전계 및 불완전계 구형 단충래티스돔이 설비시설 등에 의해 집중하중을 받을 경우 그 좌굴특성을 검토한다.

• Advances in nano research
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• 제9권3호
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• pp.147-156
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• 2020

This research is related to nonlinear stability analysis of advanced microbeams reinforced by Graphene Platelets (GPLs) considering generic geometrical imperfections and thermal loading effect. Uniform, linear and nonlinear distributions of GPLs in transverse direction have been considered. Imperfection sensitivity of post-bucking behaviors of the microbeam to different kinds of geometric imperfections have been examined. Geometric imperfection is first considered to be identical as the first buckling mode, then a generic function is employed to consider sine-type, local-type and global-type imperfectness. Modified couple stress theory is adopted to incorporate size-dependent behaviors of the beam at micro scale. The post-buckling problem is solved analytically to derive load-amplitude curves. It is shown that post-buckling behavior of microbeam is dependent on the type geometric imperfection and its magnitude. Also, post-buckling load can be enhanced by adding more GPLs or selecting a suitable distribution for GPLs.