• Structural Engineering and Mechanics
• /
• 제59권6호
• /
• pp.1139-1153
• /
• 2016

Elastic constraints are usually simplified as "spring forces" exerted on beam ends without considering the "spring deformation". The partial differential equation governing the free vibrations of a cantilever Bernoulli-Euler beam considering the deformation of elastic constraints is firstly established, and is nondimensionalized to obtain two dimensionless factors, $k_v$ and $k_r$, describing the effects of elastically vertical and rotational end constraints, respectively. Then the frequency equation for the above Bernoulli-Euler beam model is derived using the method of separation of variables. A numerical analysis method is proposed to solve the transcendental frequency equation for the continuous change of the frequency with $k_v$ and $k_r$. Then the mode shape functions are given. Finally, effects of $k_v$ and $k_r$ on free vibration characteristics of the beam with different slenderness ratios are calculated and analyzed. The results indicate that the effects of $k_v$ are larger on higher-order free vibration characteristics than on lower-order ones, and the impact strength decreases with slenderness ratio. Under a relatively larger slenderness ratio, the effects of $k_v$ can be neglected for the fundamental frequency characteristics, while cannot for higher-order ones. However, the effects of $k_r$ are large on both higher- and lower-order free vibration characteristics, and cannot be neglected no matter the slenderness ratio is large or small.

• Structural Engineering and Mechanics
• /
• 제65권1호
• /
• pp.43-51
• /
• 2018

Structural modal parameters i.e. natural frequencies, damping ratios and mode shapes are dynamic features obtained either by measuring the vibration responses of a structure or by means of finite elements models. Over the past two decades, modal parameters have been used to detect damage in structures by observing its variations over time. However, such variations can also be caused by environmental factors such as humidity, wind and, more importantly, temperature. In so doing, the use of modal parameters as damage indicators can be seriously compromised if these effects are not properly tackled. Many researchers around the world have found numerous methods to mitigate the influence of such environmental factors from modal parameters and many advanced damage indicators have been developed and proposed to improve the reliability of structural health monitoring. In this paper, several vibration tests are performed on a simply supported steel beam subjected to different damage scenarios and temperature conditions, aiming to describe the variation in modal parameters due to temperature changes. Moreover, four statistical methodologies are proposed to identify damage. Results show a slightly linear decrease in the modal parameters due to temperature increase, although it is not possible to establish an empirical equation to describe this tendency.

• 한국ITS학회 논문지
• /
• 제17권4호
• /
• pp.26-40
• /
• 2018

본 연구는 자전거사고에 영향을 주는 요인들을 분석하기 위해 PLS 구조방정식을 이용하여 자전거사고모형을 개발한다. 본 연구에서는 자전거사고를 전국 시 군 구를 대상으로 전체 사고건수, 중상이상 사고, 경상사고로 사고유형을 구분하였다. 본 연구에서 개발된 사고모형들을 통해 자전거사고의 주요 원인들을 살펴보면 도시화의 확대가 자전거사고의 가장 큰 요인임을 알 수 있다. 자전거사고모형들에 포함된 주요 요소들을 살펴보면 인구수, 경제활동인구비율, 교차로밀도, 시가화 면적비율, 상업과 공업의 토지이용, 운전면허소지자, 자동차등록대수, 교육기관 설립수, 공원수 등의 증가가 자전거사고의 증가로 이어졌다. 또한 자전거도로연장, 자전거보유대수, 자전거수단분담률의 증가 등 각 지자체 별로 활성화되고 있는 자전거이용의 확산 역시 자전거사고를 증가시키는 주요 요소들로 밝혀졌다.

• 컴퓨터교육학회논문지
• /
• 제16권1호
• /
• pp.11-22
• /
• 2013

최근 새로운 기기들의 등장으로 인터넷으로 인한 중독보다 새로운 기술들에 대한 중독이 더욱 심각한 문제를 야기하고 있다. 기존 연구에서 인터넷과 휴대폰 중독을 각각 다루고 있기는 하지만, 기술간 중독에 미치는 변인들의 상대적 중요도와 인과관계를 파악한 연구는 드물다. 본 연구는 인터넷과 휴대폰 중독에 영향을 미치는 변인간의 관계와 두 중독의 차이를 시간 관점에서 분석한다. 청소년들을 대상으로 부모나 친구와 같은 환경적 변인이 시간관이나 기기 사용시간과 같은 개인 변인에 미치는 영향과 개인 변인이 인터넷과 휴대폰 중독에 미치는 영향을 분석한다. 또한 인터넷과 휴대폰 중독에 영향을 미치는 변인간의 상대적 중요도를 구한다. 이를 위해 1,420명의 초 중 고등학생들에게 설문을 실시하고 구조 방정식 모형과 부데스크 (Budescu) 교수의 우세 분석을 실시한다. 이를 통해 인터넷과 휴대폰 중독간의 사용방법의 차이와 중요 변인을 기술하여 중독의 변화와 새로운 기술 중독에 대한 대처방법을 제언한다.

• Structural Engineering and Mechanics
• /
• 제66권4호
• /
• pp.423-438
• /
• 2018

This pioneer study focuses on finite element modeling and numerical modeling of three types of Reinforced Concrete Haunched Beams (RCHBs). Firstly, twenty RCHBs, consisting of three types, and four prismatic beams which had been tested experimentally were modeled via a nonlinear finite element method (NFEM) based software named as, ATENA. The modeling results were compared with experimental results including load capacity, deflection, crack pattern and mode of failure. The comparison showed a good agreement between the results and thus the model used can be effectively used for further studies of RCHB with high accuracy. Afterwards, new mechanism modes and design code equations were proposed to improve the shear design equation of ACI-318 and to predict the critical effective depth. These equations are the first comprehensive formulas in the literature involving all types of RCHBs. The statistical analysis showed the superiority of the proposed equation to their predecessors where the correlation coefficient, $R^2$ was found to be 0.89 for the proposed equation. Moreover, the new equation was validated using parametric and reliability analyses. The parametric analysis of both experimental and predicted results shows that the inclination angle and the compressive strength were the most influential parameters on the shear strength. The reliability analysis indicates that the accuracy of the new formulation is significantly higher as compared to available design equations and its reliability index is within acceptable limits.

• Structural Engineering and Mechanics
• /
• 제74권5호
• /
• pp.657-670
• /
• 2020

Due to the high compressive and tensile strength of ultra-high performance concrete (UHPC), UHPC used in steel concrete composite structures provided thinner concrete layer compared to ordinary concrete. This leaded to the headed stud shear connectors embedded in UHPC had a low aspect ratio. In order to systematic investigate the effect of headed stud with low aspect ratio on the structural behaviors of steel UHPC composite structure s this paper firstly carried out a test program consisted of twelve push out specimens. The effects of stud height, aspect ratio and reinforcement bars in UHPC on the structural behaviors of headed studs were investigated. The push out test results shows that the increasing of stud height did not obviously influence the structural behaviors of headed studs and the aspect ratio of 2.16 was proved enough to take full advantage of the headed stud strength. Based on the test results, the equation considering the contribution of weld collar was modified to predict the shear strength of headed stud embedded in UHPC. The modified equation could accurately predict the shear strength of headed stud by comparing with the experimental results. On the basis of push out test results, bending tests consisted of three steel UHPC composite slabs were conducted to investigate the effect of shear connection degree on the structural behaviors of composite slabs. The bending test results revealed that the shear connection degree had a significantly influence on the failure modes and ultimate resistance of composite slabs and composite slab with connection degree of 96% in s hear span exhibited a ductile failure accompanied by the tensile yield of steel plate and crushing of UHPC. Finally, analytical model based on the failure mode of composite slabs was proposed to predict the ultimate resistance of steel UHPC composite slabs with different shear connection degrees at the interface.

• Structural Engineering and Mechanics
• /
• 제87권1호
• /
• pp.1-18
• /
• 2023

The paper presents a Bayesian Finite element (FE) model updating methodology by utilizing modal data. The dynamic condensation technique is adopted in this work to reduce the full system model to a smaller model version such that the degrees of freedom (DOFs) in the reduced model correspond to the observed DOFs, which facilitates the model updating procedure without any mode-matching. The present work considers both the MPV and the covariance matrix of the modal parameters as the modal data. Besides, the modal data identified from multiple setups is considered for the model updating procedure, keeping in view of the realistic scenario of inability of limited number of sensors to measure the response of all the interested DOFs of a large structure. A relationship is established between the modal data and structural parameters based on the eigensystem equation through the introduction of additional uncertain parameters in the form of modal frequencies and partial mode shapes. A novel sampling strategy known as the Metropolis-within-Gibbs (MWG) sampler is proposed to sample from the posterior Probability Density Function (PDF). The effectiveness of the proposed approach is demonstrated by considering both simulated and experimental examples.

• 한국의류학회지
• /
• 제30권6호
• /
• pp.916-927
• /
• 2006

The purpose of this study was to identify psychological and behavioral outcomes of commitment to apparel brand community by test structural equation model. Subjects of 317 members for 9 selected apparel communities responded the questionnaire in the home-page or in the attached file. The results were as follows: 1) The suggested structural equation mode was accepted by data from apparel brand communities with hish brand strength(${\chi}^2=97.42$, d.f.=89, p=0.25, GFI=0.92, AGFI=0.88, RMR=0.05, NFI=0.94). However, this model wasn't accepted by data kom apparel brand communities with low brand strength. 2) Three types of commitment to brand community(emotional, continuous and normative commitments) influenced brand identification positively and brand identification positively influenced three types of behavioral outcomes(favorable word-of-mouth, co-production and repurchase of brand). Therefore, managements need to develop marketing programs to promote each type of commitment to their's own brand community.

• 전산구조공학
• /
• 제11권1호
• /
• pp.217-226
• /
• 1998

본 논문은 변위제약모드를 갖는 트러스구조물의 형태해석을 목적으로 하였으며, 이를 위하여 해의 존재조건과 무어-펜로즈(Moore-Penrose) 일반역행렬을 이용하였다. 또한, 수치해석과정에서의 변위제약모드로는 호몰로지변형(homologous deformation)을 고려하여 해석하였고, 다음으로 다양한 변위제약모드와 절점에 작용하는 하중비를 만족하는 구조물의 형태를 구하였다. 본 논문에서의 형태해석문제는 지정된 변위를 만족하는 구조물의 형태를 찾는 일종의 역문제(inverse problem)로서 일반적인 구조해석과정과는 반대되는 입장에서 접근하였다. 또한, 본 논문에서는 수치해석과정에서 근사해의 정도를 향상시키기 위하여 뉴튼-랩슨법을 사용하였고, 수치해석예제로서 부재의 배열형태에 따라 3가지모델을 선택하였으며, 이들 모델을 통하여 적용한 해석기법의 정확성과 효율성을 검증하였다.

• Nuclear Engineering and Technology
• /
• 제55권11호
• /
• pp.4295-4306
• /
• 2023

The vibration of fuel rods in axial flow is a universally recognized issue within both engineering and academic communities due to its significant importance in ensuring structural safety. This paper aims to thoroughly investigate the stability and nonlinear vibration of a fuel rod subjected to axial flow in a newly designed high temperature gas cooled reactor. Considering the possible presence of thermal expansion and large deformation in practical scenarios, the thermal effect and geometric nonlinearity are modeled using the von Karman equation. By applying Hamilton's principle, we derive the comprehensive governing equation for this fluid-structure interaction system, which incorporates the quadratic nonlinear stiffness. To establish a connection between the fluid and structure aspects, we utilize the Galerkin method to solve the perturbation potential function, while employing mode expansion techniques associated with the structural analysis. Following convergence and validation analyses, we examine the stability of the structure under various conditions in detail, and also investigate the bifurcation behavior concerning the buckling amplitude and flow velocity. The findings from this research enhance the understanding of the underlying physics governing fuel rod behavior in axial flow under severe yet practical conditions, while providing valuable guidance for reactor design.