• Steel and Composite Structures
• /
• 제19권4호
• /
• pp.897-916
• /
• 2015

A procedure for critical buckling moment of a tapered beam is proposed with the application of potential energy calculations using Ritz method. Respective solution allows to obtain critical moments initiating lateral buckling of the simply supported, modestly tapered steel I-beams. In particular, lateral-torsional buckling of beams with simultaneously tapered flanges and the web are considered. Detailed, numerical, parametric analyses are carried out. Typical engineering, uniformly distributed design loads are considered for three cases of the load, applied to the top flange, shear centre, as well as to the bottom flange. In addition simply supported beam under gradient moments is investigated. The parametric analysis of simultaneously tapered beam flanges and the web, demonstrates that tapering of flanges influences much more the critical moments than tapering of the web.

• 중환자간호학회지
• /
• 제10권2호
• /
• pp.56-70
• /
• 2017

Purpose: This study was conducted to identify ICU nurses' knowledge of the five moments of hand hygiene and the ambiguity of these moments when demonstrating hand hygiene. Methods: The subjects were 200 intensive care unit nurses at a university hospital. Data was collected using self-report questionnaires, translated according to the instructions of training films developed by WHO, and analyzed using descriptive statistics and ranking tests. Results: The highest number of correct answers was regarding the moment before contact with a patient and the lowest was regarding the moment after contact with a patient. The rate of providing wrong answers regarding required moments of hand hygiene was high. Conclusion: The study identified ICU nurses' knowledge of specific moments of hand hygiene; they had difficulty differentiating between the moments that happened simultaneously, i.e. after touching a patient, and that patient's surroundings, and there was ambiguity concerning patient areas and medical treatment areas. It was concluded that it is necessary to educate nurses regarding both required and unrequired moments of hand hygiene and to ensure that they can distinguish between these moments.

• 한국안전학회지
• /
• 제17권4호
• /
• pp.189-195
• /
• 2002

I-단면 곡선보 (curved beam)의 모멘트 하중 하에서 비틀림(warping)을 포함한 평면외 (out-of-plane)의 좌굴을 미분구적법 (DQM)을 이용하여 해석하였다. 다양한 경계조건(boundary conditions) 및 굽힘각(opening angles)에 따른 임계모멘트 (critical moments)를 계산하고, DQM의 해석결과는 해석적 해답 (exact solution) 과 비교 분석하였다. DQM은 적은 요소(grid points)를 사용하여 정확한 해석결과를 보여주었고, 두 경계조건 (고정-고정, 고정-단순지지)하에서 새로운 결과 또한 제시하였다.

• 한국산학기술학회논문지
• /
• 제13권7호
• /
• pp.2858-2864
• /
• 2012

곡선보 (curved beam)의 내평면 모멘트 및 등분포하중 하에서 평면내 (in-plane) 좌굴 (buckling)을 미분구적법(DQM)을 이용하여 해석하였다. 다양한 경계조건 (boundary conditions)과 굽힘각 (opening angles)에 따른 임계모멘트 및 임계하중을 계산하였다. DQM의 해석결과는 해석적 해답 (exact solution) 결과와 비교하였으며, DQM은 적은 요소 (grid points)를 사용하여 정확한 해석결과를 보여주었다. 두 경계조건(고정-고정, 단순지지-고정)하에서 새 결과를 또한 제시하였다.

• Steel and Composite Structures
• /
• 제20권1호
• /
• pp.57-70
• /
• 2016

The predominant type of buckling that I-steel concrete composite beams experience in the negative moment area is distortional buckling. The key factors that affect distortional buckling are the torsional and lateral restraints by the bottom flange. This study thoroughly investigates the equivalent lateral and torsional restraint stiffnesses of the bottom flange of an I-steel concrete composite beam under negative moments. The results show a coupling effect between the applied forces and the lateral and torsional restraint stiffnesses of the bottom flange. A formula is proposed to calculate the critical buckling stress of the I-steel concrete composite beams under negative moments by considering the lateral and torsional restraint stiffnesses of the bottom flange. The proposed method is shown to better predict the critical bending moment of the I-steel composite beams. This article introduces an improved method to calculate the elastic foundation beams, which takes into account the lateral and torsional restraint stiffnesses of the bottom flange and considers the coupling effect between them. The results show a close match in results from the calculation method proposed in this paper and the ANSYS finite element method, which validates the proposed calculation method. The proposed calculation method provides a theoretical basis for further research on distortional buckling and the ultimate resistance of I-steel concrete composite beams under a variable axial force.

• Nuclear Engineering and Technology
• /
• 제47권6호
• /
• pp.712-718
• /
• 2015

Cast duplex stainless steels are susceptible to thermal aging during long-term service at temperatures ranging from $280^{\circ}C$ to $450^{\circ}C$. To analyze the effect of thermal aging on leak-before-break (LBB) behavior, three-dimensional finite element analysis models were built for circumferentially cracked pipes. Based on the elasticeplastic fracture mechanics theory, the detectable leakage crack length calculation and J-integral stability assessment diagram approach were carried out under different bending moments. The LBB curves and LBB assessment diagrams for unaged and thermally aged pipes were constructed. The results show that the detectable leakage crack length for thermally aged pipes increases with increasing bending moments, whereas the critical crack length decreases. The ligament instability line and critical crack length line for thermally aged pipes move downward and to the left, respectively, and unsafe LBB assessment results will be produced if thermal aging is not considered. If the applied bending moment is increased, the degree of safety decreases in the LBB assessment.

• 한국공간구조학회논문집
• /
• 제6권4호
• /
• pp.81-92
• /
• 2006

본 연구는 순수 면내모멘트를 발생시키는 선형적으로 변하는 수직응력을 받고 있는 단순지지된 마주보는 두 모서리와 자유경계를 가지는 직사각형 판의 자유진동과 좌굴의 엄밀해를 구하였다. 정현적으로 가정된 하중방향(x)으로의 변위함수는 단순지지 경계조건을 만족시키며, 평판을 지배하는 편미분 운동방정식 을 y 방향으로의 변계수를 갖는 상미분방정식으로 만든다. Frobenius법을 통하여, y방향으로의 멱급수를 가정하면 이 식을 엄밀하게 풀 수 있으며, 그 식의 합당한 계수를 구할 수 있다. 자유경계조건을 y=0과 b에 적용하면, 고유진동수와 임계좌굴모멘트를 구할 수 있는 4차의 특성행렬식이 만들어진다. 본 논문에서는 이 급수해의 수렴성이 면밀히 조사되었으며, 임계 좌굴모멘트의 수치결과와 모드형상이 주어진다. 상대적으로 정확도가 떨어지는 1차원적인 보 이론으로 구한 결과치와의 비교연구가 이루어진다. 또한 자유진동수와 모드형상 주어진다. 프와송비(v)의 변화에 따른 좌굴모멘트와 고유진동수의 변화가 도표로 주어진다.

• 한국농공학회지
• /
• 제29권3호
• /
• pp.153-162
• /
• 1987

A numerical procedure for the analysis of slender arch buckling problems for uniform dead weight is presented in this paper. Such loading changes in the arch profile. The problem is nonlinear. The numerical procedure is limited to an inextensible analysis and to elastic behavior. Based upon a numerical integration technique developed by Newmark for straight beams, a large deflection bending analysis is combined with small deflection buckling routines to formulate the numerical procedure. The numerical procedure is composed of a combination of the numerical integration and successive approximations procedure. The results obtained in this study are as follows : 1.The critical loads obtained in this study coincide with the results by Austin so that the algorithm developed in this study is verified. 2.The numerical results are converged with good precision when the half arch is divided into 10 segments in both Prime and Quadratic section. 3.The critical loads are decreased as the ratios of rise versus span are increased. 4.The critical loads are increased as the moments of inertia at the ends are increased. 5.The critical loads of Prime section are larger than that of Quadratic section under the same profile conditions.

• Steel and Composite Structures
• /
• 제33권5호
• /
• pp.755-765
• /
• 2019

This study examined geometric and physical nonlinear analyses of beams and arches specifically from rolled profiles used in mining and underground constructions. These profiles possess the ability to create plastic hinges owing to their robustness. It was assumed that displacements in beams and arches fabricated from these profiles were comparable with the size of the structure. It also considered changes in the shape of a rod cross-section and the nonlinearities of the structure. The analyses were based on virtual unit moments, effective flexural rigidity of used open sections, and a secant method. The use of the approach led to a solution for the "after-critical" condition in which deformation increased with decreases in loads. The solution was derived for static determinate beams and static indeterminate arches. The results were compared with results obtained in other experimental tests and methods.

• 콘크리트학회논문집
• /
• 제12권2호
• /
• pp.53-62
• /
• 2000

Under severe lateral loads, ductile moments-resisting reinforced concrete frames will be subjected to large loads and displacements. Thus, large deformation and shear stree are occurred at the beam-column joints which are the most critical region in ductile moments-resisting system. The purpose of this study was to investigate the shear strength of beam-column connection using high strength concrete. Four subassemblies were designed 2/3 scale of read structures and tested. The obtained results are as follows. 1) The transverse beams increase the shear resistance and ductility of joint, 2) The slab was contributed to increase of the flexural capacity of the beam, but was not contributed to increase the joint ductility under cyclic loads. 3) The shear stress factors. given by the ACI code would be modified in evaluating the shear strength of beam-column joints of frame which were constructed with high-strength concrete.