• 한국전산구조공학회논문집
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• 제36권2호
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• pp.137-145
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• 2023

이 논문은 정적 재하상태에 있는 무피복 강합성보와 내화피복을 적용한 강합성보를 대상으로 화재 시 내부 온도 및 수직처짐에 대한 내화피복의 영향을 평가한 결과를 제시한다. 열응력해석을 위한 화재하중으로는 American Society for Testing and Materials E119의 표준화재곡선을 사용했으며, 강재거더 표면에 부착하는 내화재료의 방화효과를 구현하기 위해 외기에서 강합성보로 전달되는 열의 전달계수를 감소시켰다. 실규모 무피복 강합성보에 대한 구조화재실험에서 내부 온도분포와 수직처짐을 측정하였고 실험 결과와의 비교를 통해 비선형 구조화재해석 결과의 타당성을 검증하였다. 내화피복이 적용된 강합성보의 구조화재해석 결과로부터 강재거더 표면에 내화재를 적용할 경우 동일 화재 조건에서 무피복 강합성보에 비해 내부 온도와 수직처짐이 감소함을 알 수 있었다. 또한 열전달계수의 변화에 따른 열응력 응답으로부터 화재 시 강합성보의 온도 및 구조거동에 대한 내화피복의 영향을 제시하였다.

• Steel and Composite Structures
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• 제41권5호
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• pp.625-636
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• 2021

This paper examines the fire performance of uninsulated and uncoated restrained steel-concrete composite beams supplemented with externally prestressed strands through advanced numerical simulation. In this work, a sequentially coupled thermo-mechanical analysis is carried out using ABAQUS. This analysis utilizes a highly nonlinear three-dimensional finite element (FE) model that is specifically developed and validated using full-sized specimens tested in a companion fire testing program. The developed FE model accounts for nonlinearities arising from geometric features and material properties, as well as complexities resulting from prestressing systems, fire conditions, and mechanical loadings. Four factors are of interest to this work including effect of restraints (axial vs. rotational), degree of stiffness of restraints, the configuration of external prestressed tendons, and magnitude of applied loading. The outcome of this analysis demonstrates how the prestressing force in the external tendons is primarily governed by the magnitude of applied loading and experienced temperature level. Interestingly, these results also show that the stiffness of axial restraints has a minor influence on the failure of restrained and prestressed steel-concrete composite beams. When the axial restraint ratio does not exceed 0.5, the critical deflection of the composite beam is lower than that of the composite beam with a restraint ratio of 1.0.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3379-3397
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• 2021

In this study, a multi-physics modeling method was developed to analyze a nuclear fuel rod's thermo-mechanical behavior especially for high temperature anisotropic creep deformation during ballooning and burst occurring in Loss of Coolant Accident (LOCA). Based on transient heat transfer and nonlinear mechanical analysis, the present work newly incorporated the nuclear fuel rod's special characteristics which include gap heat transfer, temperature and burnup dependent material properties, and especially for high temperature creep with material anisotropy. The proposed method was tested through various benchmark analyses and showed good agreements with analytical solutions. From the validation study with a cladding burst experiment which postulates the LOCA scenario, it was shown that the present development could predict the ballooning and burst behaviors accurately and showed the capability to predict anisotropic creep behavior during the LOCA. Moreover, in order to verify the anisotropic creep methodology proposed in this study, the comparison between modeling and experiment was made with isotropic material assumption. It was found that the present methodology with anisotropic creep could predict ballooning and burst more accurately and showed more realistic behavior of the cladding.

• 한국추진공학회지
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• 제20권6호
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• pp.46-53
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• 2016

희박 예혼합 가스터빈의 연소 불안정 현상을 이해하기 위해서는, 선형 과정에 의하여 얻어지는 고유주파수 및 초기 성장률뿐만 아니라, 연소기 비선형 특성에 의존하는 한계진폭의 예측이 필요하다. 특히 현재의 연구에서는 비선형 거동에 의한 한계 진폭을 예측하기 위해서 유동 섭동과 열발생의 비율이 주파수와 속도 진폭을 정의할 수 있는 화염묘사함수를 적용하였다. 본 연구에서는 화염묘사함수를 얻기 위하여 CFD 기법이 적용되었으며, 이를 통하여 비선형 열음향 해석으로부터 불안정 한계 진폭을 예측할 수 있었다.

• Smart Structures and Systems
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• 제9권6호
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• pp.505-534
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• 2012

The present work deals with second order statistics of post buckling response of piezoelectric laminated composite cylindrical shell panel subjected to hygro-thermo-electro-mechanical loading with random system properties. System parameters such as the material properties, thermal expansion coefficients and lamina plate thickness are assumed to be independent of the temperature and electric field and modeled as random variables. The piezoelectric material is used in the forms of layers surface bonded on the layers of laminated composite shell panel. The mathematical formulation is based on higher order shear deformation shell theory (HSDT) with von-Karman nonlinear kinematics. A efficient $C^0$ nonlinear finite element method based on direct iterative procedure in conjunction with a first order perturbation approach (FOPT) is developed for the implementation of the proposed problems in random environment and is employed to evaluate the second order statistics (mean and variance) of the post buckling load of piezoelectric laminated cylindrical shell panel. Typical numerical results are presented to examine the effect of various environmental conditions, amplitude ratios, electrical voltages, panel side to thickness ratios, aspect ratios, boundary conditions, curvature to side ratios, lamination schemes and types of loadings with random system properties. It is observed that the piezoelectric effect has a significant influence on the stochastic post buckling response of composite shell panel under various loading conditions and some new results are presented to demonstrate the applications of present work. The results obtained using the present solution approach is validated with those results available in the literature and also with independent Monte Carlo Simulation (MCS).

• Coupled systems mechanics
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• 제7권4호
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• pp.373-393
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• 2018

This paper is concerned with the wave propagation behavior of rotating functionally graded temperature-dependent nanoscale beams subjected to thermal loading based on nonlocal strain gradient stress field. Uniform, linear and nonlinear temperature distributions across the thickness are investigated. Thermo-elastic properties of FG beam change gradually according to the Mori-Tanaka distribution model in the spatial coordinate. The nanobeam is modeled via a higher-order shear deformable refined beam theory which has a trigonometric shear stress function. The governing equations are derived by Hamilton's principle as a function of axial force due to centrifugal stiffening and displacement. By applying an analytical solution and solving an eigenvalue problem, the dispersion relations of rotating FG nanobeam are obtained. Numerical results illustrate that various parameters including temperature change, angular velocity, nonlocality parameter, wave number and gradient index have significant effect on the wave dispersion characteristics of the understudy nanobeam. The outcome of this study can provide beneficial information for the next generation researches and exact design of nano-machines including nanoscale molecular bearings and nanogears, etc.

• Steel and Composite Structures
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• 제27권3호
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• pp.311-325
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• 2018

This article presents the bending analysis of FGM rectangular plates resting on non-uniform elastic foundations in thermal environment. Theoretical formulations are based on a recently developed refined shear deformation theory. The displacement field of the present theory is chosen based on nonlinear variations in the in-plane displacements through the thickness of the plate. The present theory satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. Unlike the conventional trigonometric shear deformation theory, the present refined shear deformation theory contains only four unknowns as against five in case of other shear deformation theories. The material properties of the functionally graded plates are assumed to vary continuously through the thickness, according to a simple power law distribution of the volume fraction of the constituents. The elastic foundation is modeled as non-uniform foundation. The results of the shear deformation theories are compared together. Numerical examples cover the effects of the gradient index, plate aspect ratio, side-to-thickness ratio and elastic foundation parameters on the thermo-mechanical behavior of functionally graded plates. Numerical results show that the present theory can archive accuracy comparable to the existing higher order shear deformation theories that contain more number of unknowns.

• Steel and Composite Structures
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• 제20권3호
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• pp.651-669
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• 2016

The behavior of shear connectors plays a significant role in maintaining the required strength of a composite beam in normal and hazardous conditions. Various types of shear connectors are available and being utilized in the construction industry according to their use. Channel connectors are a suitable replacement for conventional shear connectors. These connectors have been tested under different types of loading at ambient temperature; however, the behavior of these connectors at elevated temperatures has not been studied. This investigation proposes a numerical analysis approach to estimate the behavior of channel connectors under fire and compare it with the numerical analysis performed in headed stud and Perfobond shear connectors subjected to fire. This paper first reviews the mechanism of various types of shear connectors and then proposes a non-linear thermo-mechanical finite element (FE) model of channel shear connectors embedded in high-strength concrete (HSC) subjected to fire. Initially, an accurate nonlinear FE model of the specimens tested at ambient temperature was developed to investigate the strength of the channel-type connectors embedded in an HSC slab. The outcomes were verified with the experimental study performed on the testing of channel connectors at ambient temperature by Shariati et al. (2012). The FE model at ambient temperature was extended to identify the behavior of channel connectors subjected to fire. A comparative study is performed to evaluate the performance of channel connectors against headed stud and Perfobond shear connectors. The channel connectors were found to be a more economical and easy-to-apply alternative to conventional shear connectors.

• 한국지반공학회논문집
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• 제39권5호
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• pp.51-63
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• 2023

계절성 동토의 온도 변화에 따른 융해 및 동결작용에 의한 지반의 거동이 말뚝 기초의 변위 및 지지력에 끼치는 영향을 파악하기 위한 수치해석을 수행하였다. 수치해석은 온도 변화에 따른 지반-말뚝 상호작용을 모사하기 위해 유한요소법 기반의 TM 모델링(Thermo-Mechanical coupled Modeling)을 적용하였으며, 동결 지반은 온도 의존적 비선형 물성을 적용하였다. 지반의 구성 모델은 소성 거동을 모사하기 위한 MCR 모델(Mohr Coulomb with Rankine Tensile cut-off Model)과 HDP 모델(Nonlinear Hyperbolic Drucker-Prager Model)을 각각 적용하였으며, 말뚝의 길이 및 너비 조건을 선정해 수치해석 결과를 비교 및 분석하였다. 수치해석 결과는 HDP 구성 모델이 비교적 작은 지반 거동과 지지력을 보였으나, 전체적으로는 말뚝의 길이 및 너비 조건에 따라 지지력 및 말뚝 머리의 변위 결과의 양상과 그 크기는 유사하게 나타났다. 지반의 융해-동결작용으로 인한 말뚝 머리(pile head)의 수직 변위는 길이 조건이 짧을수록 변위의 변화 폭이 크게 나타났다. 수직 변위는 길이 조건에 따라 MCR 구성 모델에서는 최대 0.0387m의 융해 침하와 0.0277m의 동결 융기가 발생했으며, HDP 구성 모델에서는 최대 0.0367m의 융해 침하와 0.0264m의 동결 융기가 발생했다. 또한 두 탄소성 모델에 대한 말뚝의 지지력 결과는 말뚝의 길이 조건보다 너비 조건에서 더 큰 차이를 보였으며, 너비 조건 L에서 최대 약 14.7%, M에서 최대 약 5.4%, S에서 최대 약 5.3%가 발생하였다. 이에 말뚝 머리의 수직 변위와 말뚝의 지지력은 말뚝-지반의 접촉 면적에 영향을 크게 받으며, 지반 내 활성층의 활성도에 따라 차이를 보였다.