• Earthquakes and Structures
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• 제16권1호
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• pp.119-127
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• 2019

When a structural wall is subjected to multi-directional ground motion, torsion-induced cracks degrade the stiffness of the wall. The effect of torsion should not be neglected. As a main lateral load resisting member, reinforced concrete (RC) structural wall has been widely studied under the combined action of bending and shear. Unfortunately, its seismic behavior under a combined action of torsion, bending and shear is rarely studied. In this study, torsional performances of the RC structural walls under the combined action is assessed from a comprehensive parametrical study. Finite element (FE) models are built and calibrated by comparing with the available experimental data. The study is then carried out to find out the critical design parameter affecting the torsional stiffness of RC structural walls, including the axial load ratio, aspect ratio, leg-thickness ratio, eccentricity of lateral force, longitudinal reinforcement ratio and transverse reinforcement ratio. Besides, to facilitate the application in practice, an empirical equation is developed to estimate the torsional stiffness of RC rectangular structural walls conveniently, which is found to agree well with the numerical results of the developed FE models.

• Composites Research
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• 제27권6호
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• pp.207-212
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• 2014

The shape optimization of composite flexbeam sections of a bearingless helicopter rotor is studied using a finite element (FE) sectional analysis integrated with an efficient evolutionary optimization algorithm called particle swarm assisted genetic algorithm (PSGA). The sectional optimization framework is developed by automating the processes for geometry and mesh generation, and the sectional analysis to compute the elastic and inertial properties. Several section shapes are explored, modeled using quadratic B-splines with control points as design variables, through a multiobjective design optimization aiming minimum torsional stiffness, lag bending stiffness, and sectional mass while maximizing the critical strength ratio. The constraints are imposed on the mass, stiffnesses, and critical strength ratio corresponding to multiple design load cases. The optimal results reveal a simpler and better feasible section with double-H shape compared to the triple-H shape of the baseline where reductions of 9.46%, 67.44% and 30% each are reported in torsional stiffness, lag bending stiffness, and sectional mass, respectively, with critical strength ratio greater than 1.5.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.480-485
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• 2004

The applications of composite materials have increased over the past few decades in a variety of structures that require high ratio of stiffness and strength to weight ratios. Recently the thick open section composite beams are used extensively as load carrying members and stiffeners of structural elements. However, most of studies on thick composite beams are limited only to closed section beams. In this study, an open cross-section thick-walled composite beam model which includes coupled stiffness, transverse shear, and warping effects is suggested and the deflections associated with the thick-walled composite beams and thin-walled composite beams are obtained and compared with the finite element analysis results.

• 한국구조물진단유지관리공학회 논문집
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• 제9권1호
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• pp.159-170
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• 2005

격자구조는 병렬하는 주거더에 횡거더로 접합된 구조를 말하며 집중하중이 재하될 때 하중이 주거더만 부담하지 않고 횡거더를 통하여 다른 주거더로 하중이 일부를 부담하게 된다. 격자형의 교량은 과다한 집중하중을 분산시켜 내하력이 높은 특성을 갖고 있으며 사용재료를 절약할 수 있어 경제적이다. 본 연구에서는 해석절차가 간단하고 이해가 쉬운 전달행렬법을 이용하여 격자교의 프로그램을 작성하여 Leonhardt, Szabo, FEM, 양창현 및 정진환의 해석결과와 비교하였다. 또한, 경사각을 갖는 직선격자교와 곡선격자교의 특성을 분석하였고, 경사각과 휨강도/비틀림강도의 비에 따른 직선격자교와 곡선격자교의 단면력을 분석하였다.

• Earthquakes and Structures
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• 제20권4호
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• pp.431-444
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• 2021

T-shaped column is usually used as side column in buildings, which is one of the weak members in structural system. This paper presented a quasi-static cyclic loading experiment of six specimens of reinforced concrete (RC) T-shaped columns under compression-flexure-shear-torsion combined loadings to investigate the effect in the ratio of torsion to moment (T/M) and axial compression ratio (n) and height-thickness ratio of flange plate (φ) on their seismic performance. Based on the test results, the failure characteristics, hysteretic curves, ductility, energy dissipation, stiffness degradation and strength degradation were analyzed. The results show that the failure characteristics of RC T-shaped columns mainly depend on the ratio of torsion to moment, which can be divided into bending failure, bending-torsion failure and shear-torsion failure. With the increase of T/M ratio, the torsion ductility coefficient increased, and in a suitable range, the torsion and horizontal displacement ductility coefficient of RC T-shaped columns could be effectively improved with the increase of axial compression ratio and the decrease of height-thickness ratio of flange plate. Besides, the energy dissipation capacity of the specimens mainly depended on the bending and shear energy dissipation capacity. On the other hand, the increase of axial compression ratio and the ratio of torsion to moment could accelerate the torsional and bending stiffness degradation of RC T-shaped columns. Moreover, the degradation coefficient of torsion strength was between 0.80 and 0.98, and that of bending strength was between 0.75 and 1.00.

• International Journal of Aerospace System Engineering
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• 제6권2호
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• pp.1-10
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• 2019

In this paper, the probabilistic free vibration analysis of a geometrically coupled cantilever wing with uncertain material properties is carried out using stochastic finite element (SFEM) based on first order perturbation technique. Here, both stiffness and damping of the system are considered as random parameters. The bending and torsional rigidities are assumed as spatially varying second order Gaussian random fields and represented by Karhunen Loeve (K-L) expansion. Here, the expected value, standard deviation, and probability distribution of random natural frequencies and damping ratios are computed. The results obtained from the present approach are also compared with Monte Carlo simulations (MCS). The results show that the uncertain bending rigidity has more influence on the damping ratio and frequency of modes 1 and 3 while uncertain torsional rigidity has more influence on the damping ratio and frequency of modes 2 and 3.

• Composites Research
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• 제27권2호
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• pp.37-41
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• 2014

섬유강화복합재료는 비강도와 비강성이 뛰어나 여러 분야에 걸쳐 사용량이 증가하고 있으며 자전거와 같은 스포츠 용품에도 사용량이 점점 증가하고 있다. 복합재료는 다양한 형상의 구조부품으로 만들어져 사용되고 있다. 특히 자전거 프레임의 일부에는 사각형 복합재 튜브 형태로 제작되어 사용되고 있으나 이에 관한 연구는 많지 않다. 사각 복합재 튜브의 경우에 모서리에 적절한 라운드 값을 주어 굽힘과 비틀림에 견디도록 설계된다. 본 연구에서는 모서리의 곡률반경이 R5, R10, R15인 세 개의 그룹에 가로-세로 1:1, 1:1.5, 1:2의 형상비를 갖는 아홉 종류의 사각 복합재 튜브를 제작하였다. 탄소섬유강화복합재료가 튜브제작에 사용되었으며 단면적은 모두 같도록 설계되었다. $[0/90/{\pm}45]s$으로 적층하여 제작한 사각 복합재 튜브에 굽힘과 비틀림 하중을 가하여 실험평가를 수행하였다. 실험결과 사각 복합재 튜브의 R 값과 형상비에 따라서 굽힘 및 비틀림 특성이 크게 다름을 알 수 있었다.

• 한국강구조학회 논문집
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• 제15권3호
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• pp.231-239
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• 2003

과거 수 십년 동안 강박스 거더 교량은 휨과 비틀림에 대한 저항능력과 미적인 측면에서의 우수성으로 인해 많은 시공현장에서 건설되었다. 그러나 박스거더는 편재하된 하중 상태에서 단면의 뒤틀림과 뒴 현상을 경험하게 되는데 이는 박스거더의 단점으로 작용한다. 그러한 뒤틀림과 뒴 현상에 의해 발생하는 뒤틀림 응력들을 제어하기 위해서 일반적으로 박스거더 내부에 다이아프램을 설치하게 된다. 현재까지 건설된 강박스 거더 교량의 다이아프램의 형태는 충복 형태, 프레임 형태 그리고 트러스 형태 등이다. 본 연구의 목적은 매개변수 연구를 통해서 적절한 다이아프램 강성 비를 산정 하는 것과 산정된 강성 비에 근거하여 내부 다이아프램의 간격과 수를 제안하는 것이다. 대상교량은 단실 단면을 갖는 연속화된 직선 강박스 거더 교량이고, 주요한 매개변수는 단면의 형상, 경간 수, 등가 지간장, 내부 다이아프램 강성 그리고 내부 다이아프램 간격 등이다. 매개변수 연구를 통해서 적절한 내부 다이아프램 강성 비의 산정 그리고 내부 다이아프램의 간격과 수가 제안될 것이다.

• 한국공간구조학회논문집
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• 제22권1호
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• pp.33-40
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• 2022

When the center of stiffness and the center of mass of the structure differ under the seismic load, torsion is caused by eccentricity. In this study, an analysis model was modeled in which the positions of the core and the plane rotation axis of a 60-story torsional atypical structure with a plane rotation angle of 1 degree per floor were different. The structural behavior of the analysis model was analyzed, and the earthquake response behavior of the structure was analyzed based on the time history analysis results. As a result, as the eccentricity of the structure increased, the eccentricity response was amplified in the high-rise part, and the bending and torsional behavior responses were complex in the low-order vibration mode. As a result of the analysis, the maximum displacement and story drift ratio increased due to the torsional behavior. The maximum story shear force and the story absolute maximum acceleration showed similarities for each analysis model according to the shape of the vibration mode of the analysis model.

• EDISON SW 활용 경진대회 논문집
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• 제5회(2016년)
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• pp.175-182
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• 2016

Recently, carbon fiber-reinforced composite is widely used in many aerospace applications. Among most of the aerospace vehicles, human-powered aircraft essentially uses it for minimizing the weight of the vehicle and gaining high stiffness to increase its efficiency. In this paper, main wing spar of the human-powered aircraft is investigated. Finite element models were created based on the baseline model built in 2013 to make analysis of cross-section of the spar with varying ply angles of each layer of the spar. Objective function, which is affected from bending rigidity, torsional rigidity, and strength ratio, was evaluated for every cases. The model of 2013 and present cases were put into comparison by values evaluated from objective function. From the comparison, it was concluded that there are more chances to improve the baseline model to make the vehicle better in stiffness and weight than the model of 2013.