• Earthquakes and Structures
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• v.16 no.1
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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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• v.27 no.6
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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.

• Proceedings of the KSME Conference
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• 2004.11a
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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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.159-170
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• 2005

The grid structure is parallel main girders intersected with crossgirder. It distribute the loads to adjoining main girder through the crossgirder when a girder is subjected to a load. grillage girder bridge has high load-carrying capacity, it can save materials and become more economical type of bridge. In this paper, the grillage girder bridge analysis program developed by using the transfer matrix method deals with following problems: the comparision with Leonhardt, Szabo, FEM yang and jung in the analysis of grillage girder bridges, quality of straight and curved bridges with skew angle, forces of straight and curved bridges according to skew angle and bending stiffness/torsional stiffness ratio.

• Earthquakes and Structures
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• v.20 no.4
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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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• v.6 no.2
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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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• v.27 no.2
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• pp.37-41
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• 2014

Fiber reinforced composite materials have outstanding specific strength and specific stiffness. So the use of composite materials increases in various kinds of industrial fields including sports goods such as bicycles. Composite materials are used to make structural parts with various kinds of shapes. Specially, rectangular composite tubes are used to make a few of composite bicycle frames, but there has been a few of research on this issue. Rectangular composite tubes are designed to have appropriate radius of curvature and endure bending and torsional loads. In this research, nine kinds of rectangular composite tubes having aspect ratios 1:1, 1:1.5, 1:2 and radius of curvatures R5, R10, R15 were fabricated. The carbon fiber reinforced composite material was used to make tubes having same cross sectional areas. The stacking sequence of tubes is $[0/90/{\pm}45]s$. Experimental evaluation was accomplished to apply bending and torsional load to the tubes. Experimental results show that bending and torsional characteristics depend on radius of curvature and aspect ratio of rectangular composite tubes.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.231-239
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• 2003

Many box girder bridges have been constructed during the past several decades due to their large bending and torsional rigidities as well as aesthetic considerations. However, box girders have shortcoming in that the cross section distorts under an eccentric loading and warps out of the section plane. Therefore, in order to reduce distortional stresses such as distortional warping and transverse bending normal stresses, diaphragms were generally installed in the box girders. Shapes of the diaphragms in steel-box-girder bridges constructed up to date were solid-plate, frame, and truss types. The objectives of this study using parametric study were to evaluate the appropriate stiffness ratio of intermediate diaphragms and then to propose the effective spacing and numbers of intermediate diaphragms based on the evaluated stiffness ratio. Target bridges for this study were straight continuous span bridges with a single-cell steel box section. The parameters for the parametric study were the shape of box section, the span numbers, the equivalent span length, the stiffness of intermediate diaphragms, and the spacing of intermediate diaphragms. From the results of the parametric study, the effective spacing and numbers as well as the stiffness ratio of the intermediate diaphragms will be presented.

• Journal of Korean Association for Spatial Structures
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• v.22 no.1
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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.

• Proceeding of EDISON Challenge
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• 2016.03a
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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.