• Structural Engineering and Mechanics
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• 제18권4호
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• pp.389-410
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• 2004

In this study, theoretical and experimental results are presented which were obtained during an investigation of the influence of the $P-{\Delta}$ effect that was caused by the simultaneous changing of the axial load P of the column and the lateral displacement ${\Delta}$ in the external beam-column joints. The increase or decrease of ${\Delta}$ was simultaneous with the increase or decrease of the axial compression load P and caused an additional influence on the aseismic mechanical properties of the joint. A total of 12 reinforced concrete exterior beam-column subassemblies were examined. A new model, which predicts the beam-column joint ultimate shear strength, was used in order to predict the seismic behaviour of beam-column joints subjected to earthquake-type loading plus variable axial load and $P-{\Delta}$ effect. Test data and analytical research demonstrated that axial load changes and $P-{\Delta}$ effect during an earthquake cause significant deterioration in the earthquake-resistance of these structural elements. It was demonstrated that inclined bars in the joint region were effective for reducing the unfavourable impact of the $P-{\Delta}$ effect and axial load changes in these structural elements.

• Structural Engineering and Mechanics
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• 제43권5호
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• pp.561-582
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• 2012

Despite popularity of FEM in analysis of static and dynamic structural problems and the routine applicability of FE softwares, analytical methods based on simple mathematical relations is still largely sought by many researchers and practicing engineers around the world. Development of such analytical methods for analysis of free vibration of non-prismatic beams is also of primary concern. In this paper a new and simple method is proposed for determination of vibration frequencies of non-prismatic beams under variable axial forces. The governing differential equation is first obtained and, according to a harmonic vibration, is converted into a single variable equation in terms of location. Through repetitive integrations, integral equation for the weak form of governing equation is derived. The integration constants are determined using the boundary conditions applied to the problem. The mode shape functions are approximated by a power series. Substitution of the power series into the integral equation transforms it into a system of linear algebraic equations. Natural frequencies are determined using a non-trivial solution for system of equations. Presented method is formulated for beams having various end conditions and is extended for determination of the buckling load of non-prismatic beams. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained to those obtained using available finite element software.

• 한국지진공학회논문집
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• 제10권4호
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• pp.35-44
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• 2006

이 연구의 목적은 변동 축하중을 받는 중공 철근콘크리트 교각의 비탄성 거동을 파악하는데 있다. 변동 축하중은 연성도, 강도, 강성, 에너지 소산 등에 큰 영향을 미친다. 사용된 프로그램은 철근콘크리트 구조물의 해석을 위한 RCAHEST이다. 재료적 비선형성에 대해서는 균열콘크리트에 대한 인장, 압축, 전단모델과 콘크리트 속에 있는 철근모델을 조합하여 고려하였다. 이 연구에서는 변동 축하중을 받는 중공 철근콘크리트 교각의 비탄성 거동의 파악을 위해 제안한 해석기법을 신뢰성 있는 연구자의 실험결과와 비교하여 그 타당성을 검증하였다.

• Steel and Composite Structures
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• 제19권5호
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• pp.1299-1319
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• 2015

This paper presents a detailed parametric study, conducted using finite element tools to cover a range of several geometric and material parameters, on the behaviour of thin-walled partially encased composite (PEC) columns. The PEC columns studied herein are composed of thin-walled built-up H-shaped steel sections with concrete infill cast between the flanges. Transverse links are provided between the opposing flanges to improve resistance to local buckling. The parametric study is confined to eccentrically-loaded columns subjected to major axis bending only. The parameters that were varied include the overall column slenderness ratio (L/d), load eccentricity ratio (e/d), link spacing-to-depth ratio (s/d), flange plate slenderness ratio (b/t) and concrete compressive strength ($f_{cu}$). The overall column slenderness ratio was chosen to be the primary variable with values of 5, 10 and 15. Other parameters were varied within each case of L/d ratio. The effects of the selected parameters on the behaviour of PEC columns were studied with respect to the failure mode, peak axial load, axial load versus average axial strain response, axial load versus lateral displacement response, moment versus lateral displacement behaviour and the axial load-moment interaction diagram. The results of the parametric study are presented in the paper and the influences of each of the parameters investigated are discussed.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.97-106
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• 2018

Improved load-following capability is one of the most important technical tasks of a pressurized water reactor. Controlling the nuclear reactor core during load-following operation leads to some difficulties. These difficulties mainly arise from nuclear reactor core limitations in local power peaking: the core is subjected to sharp and large variation of local power density during transients. Axial offset (AO) is the parameter usually used to represent the core power peaking. One of the important local power peaking components in nuclear reactors is axial power peaking, which continuously changes. The main challenge of nuclear reactor control during load-following operation is to maintain the AO within acceptable limits, at a certain reference target value. This article proposes a new robust approach to AO control of pressurized water reactors during load-following operation. This method uses robust feedback-linearization control based on the multipoint kinetics reactor model (neutronic and thermal-hydraulic). In this model, the reactor core is divided into four nodes along the reactor axis. Simulation results show that this method improves the reactor load-following capability in the presence of parameter uncertainty and disturbances and can use optimum control rod groups to maneuver with variable overlapping.

• 한국강구조학회 논문집
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• 제15권1호
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• pp.9-15
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• 2003

최근 건축물의 고층화 및 장스팬화 됨에 따라서 부재단면이 점차 증대되서 용접시공 등이 어려워지고 있다. 이에 대한 해결방안의 하나로 고강도강을 사용하면 부재단면을 감소시킬 수 있다. 고강도강의 주 사용 부위은 높은 축력을 받는 기둥재이다. 휨모멘트와 축력을 동시에 받는 박스형 및 H형 단면을 갖는 고강도 기둥부재의 성능실험을 축력과 세장비를 변수로 수행하였다. 실험 결과 기둥부재의 최대내력이 허용응력도 설계법과 한계상태 설계법을 모두 만족하였다.

• Structural Engineering and Mechanics
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• 제24권5호
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• pp.621-639
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• 2006

Stability of a cylindrical shell subject to a uniform axial compression, which is a power function of time, is examined within the framework of small strain elasto-plasticity. The material of the shell is incompressible and the effect of the elastic unloading is considered. Initially, employing the infinitesimal elastic-plastic deformation theory, the fundamental relations and Donnell type stability equations for a cylindrical shell have been obtained. Then, employing Galerkin's method, those equations have been reduced to a time dependent differential equation with variable coefficient. Finally, for two initial conditions applying a Ritz type variational method, the critical static and dynamic axial loads, the corresponding wave numbers and dynamic factor have been found. Using those results, the effects of the variations of loading parameters and the variations of power of time in the axial load expression as well as the variations of the radius to thickness ratio on the critical parameters of the shells for two initial conditions are also elucidated. Comparing results with those in the literature validates the present analysis.

• 한국강구조학회 논문집
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• 제12권1호통권44호
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• pp.9-16
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• 2000

본 연구는 중심 압축을 받는 각형 CFT 단주의 하중-변형도 관계를 추정하기 위한 재료의 응력도-변형도 관계 모델화에 관한 것이다. 수정된 모델은 미일공동연구 결과식 형태를 기본으로 하여 본 연구자가 수행했던 실험결과로 수정된 것이다. 궁극적인 목적은 콘크리트와 강관의 강도 변화에 따른 거동 특성을 평가하기 위한 기초 자료의 제공에 있다.

• Tribology and Lubricants
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• 제25권5호
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• pp.292-297
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• 2009

Air foil thrust bearings are the critical components available on high-efficiency turbomachinery which need an ability to endure the large axial force. Air foil bearings are self-acting hydrodynamic bearings that use ambient air as their lubricant. Since the air is squeezed by the edge of compliance-surface of bearing, hydrodynamic force is generated. In this study, we measured the air film thickness and obtained the minimum film thickness experimentally. To increase the maximum load capacity, compliance of sub-structure was controlled. From numerical analyses, it is seen that, if the air film thickness is distributed more uniformly by variable compliance, the thrust bearings can take more axial load.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 추계학술대회 논문집
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• pp.78-81
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• 2002

The paper discuses characteristics of an axial-flux permanent-magnet generator for a gearless wind energy system which aims to be satisfied with variable operating conditions. Design and construction of an axial-flux permanent- magnet generator with power output at 60[Hz], 300[r/min] for wind energy system is introduced. Finite-element method (FEM) is applied to analyze generator performance at variable load. The results of FE analysis show this generator Is feasible for use with a wind turbine.