• Wind and Structures
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• 제11권2호
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• pp.153-178
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• 2008

Based on the empirical formulas for power spectra of generalized modal forces and local fluctuating wind forces in across-wind and torsional directions, the wind-induced lateral-torsional coupled response analysis of a representative rectangular tall building was conducted by setting various parameters such as eccentricities in centers of mass and/or rigidity and considering different torsional to lateral stiffness ratios. The eccentricity effects on the lateral-torsional coupled responses of the tall building were studied comprehensively by structural dynamic analysis. Extensive computational results indicated that the torsional responses at the geometric center of the building may be significantly affected by the eccentricities in the centers of mass and/or rigidity. Covariance responses were found to be in the same order of magnitude as the along-wind or across-wind responses in many eccentricity cases, suggesting that the lateral-torsional coupled effects on the overall wind-induced responses can not be neglected for such situations. The calculated results also demonstrated that the torsional motion contributed significantly to the total responses of rectangular tall buildings with mass and/or rigidity eccentricities. It was shown through this study that the framework presented in this paper provides a useful tool to evaluate the wind-induced lateral-torsional coupled responses of rectangular buildings, which will enable structural engineers in the preliminary design stages to assess the serviceability of tall buildings, potential structural vibration problems and the need for a detailed wind tunnel test.

• Earthquakes and Structures
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• 제13권1호
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• pp.9-15
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• 2017

In this paper, the influence of the rotational component, about a vertical axis, of earthquake ground motion on the response of building structures subjected to seismic action is considered. The torsional component of ground motion is generated from the records of translational components. Torsional component of ground motion is then, together with translational components, applied in numerical linear dynamic analysis of different reinforced concrete framed structure of three stories buildings. In total, more than 40 numerical models were created and analyzed. The obtained results show clearly the dependence of the effects of the torsional seismic component on structural system and soil properties. Thus, the current approach in seismic codes of accounting for the effects of accidental torsion due to the torsional ground motion, by shifting the center of mass, should be reevaluated.

• 한국공간구조학회논문집
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• 제12권2호
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• pp.65-72
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• 2012

본 연구에서는 비틀림 거동을 일으키는 편심구조물의 효율적인 제어를 위한 비틀림 강성을 가지는 동조질량감쇠기의 제어성능을 검토하고자 한다. 이를 위하여 지진하중을 받는 편심구조물에 동조질량감쇠기의 설치위치와 비틀림강성에 따른 제어성능을 평가한다. 반복되는 시간이력해석시 소요되는 해석시간을 줄이기 위하여 등가해석 모델을 사용하였고 비비례감쇠시스템인 동조질량감쇠가 설치된 구조물의 해석을 효율적으로 수행할 수 있었다. 본 연구를 통하여 일반적인 동조질량감쇠기에서 무시되어온 동조질량감쇠기의 비틀림 속성이 비틀림 거동이 발생하는 편심구조물에서는 효과적일 수 있음을 검증하였다. 그리고 편심구조물의 경우에는 동조질량감쇠기의 최적 설치 위치가 구조물 평면의 중심이 아닐 수 있음을 확인하였다.

• International Journal of Concrete Structures and Materials
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• 제11권1호
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• pp.45-58
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• 2017

Recent investigations have pointed out that current code provisions specifying that the stiffness of reinforced concrete elements is strength independent, and therefore can be estimated prior to any strength assignment, is incorrect. A strength allocation strategy, suitable for preliminary structural design of medium height wall-frame dual systems, is presented for allocating strength in such buildings and estimating the dependable rigidities. The design process may be implemented by either the approximate continuous approach or the stiffness matrix method. It is based on the concept of the inelastic equivalent single-degree-of-freedom system which, the last few years, has been used to implement the performance based seismic design. The aforesaid strategy may also be used to determine structural configurations of minimum rotation distortion. It is shown that when the location of the modal centre of rigidity, as described in author's recent papers, is within a close distance from the mass axis the torsional response is mitigated. The methodology is illustrated in ten story building configurations, whose torsional response is examined under the ground motion of Kobe 1995, component KJM000.

• Journal of Biosystems Engineering
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• 제27권4호
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• pp.283-292
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• 2002

Mechanical and physical properties of various parts of jujube (Zizyphus jojoba Miller) such as fruits, leaves, secondary branches, and leafy stems were measured and analyzed. The physical dimensions of the fruits were measured using a digital caliper, and the detachment force of the fruit and leafy stems was measured using a force gauge. The physical characteristics of the secondary branches such as the modulus of elasticity and the torsional rigidity were tested using a universal testing machine (UTM). The physical characteristics of leafy stems such as length and weight were also measured using a digital caliper and a digital scale, respectively. The detachment force of leafy stems and the area of the leaf also measured. The terminal velocities of the jujube fruits, leaves, and leafy stems were measured using a custom made terminal velocity experiment system. Diameter of the major and minor axis of the jujube fruit, weight of the fruit, and detachment force of the fruit stem was average of 32.02 mm, 23.92 mm. 10.0 ${\times}$ 10$\^$6/ ㎥, 8.99 g, and 5.43 N. respectively. The detachment forces of the jujube fruits increased and the force-to-weight ratio of the jujube fruits decreased as the weight of the jujube fruits increased. The modulus of elasticity of the secondary branches of the jujube was average of 7.01 ${\times}$ 10$\^$8/ N/㎡ and decreased as diameter of the secondary branches increased. The average torsional rigidity of the secondary jujube branches was 5.2 ${\times}$ 10$\^$-/ N/㎡, and the torsional rigidity decreased as the secondary branch diameter increased. The distribution of the torsional rigidity data associated with the diameter of the branches, however. widely scattered and it was difficult to find any relationship between the diameter of the branches and the torsional rigidity of tile branches. The weight of the leafy stems, number of loaves attached to the leafy stems, diameter of the stem side of the leafy stems, diameter of the leafy stem end was average or 0.7 g, 6.6 ea, 12.2 cm, 4.5 mm, and 2.7 mm, respectively. The major and minor axis of the .jujube loaves, area of leaves, weight of the leaves. and detachment force of the leaves was average of 5.7 cm, 3.3 cm, 12.98 cm$^2$, 0.20 g, and 4.39 N, respectively. The terminal velocity of the .jujube fruits increased as the weight of the fruits increased. The terminal velocity of the leafy stems, however, did not show a relationship with the weight of the leafy stems and the number of leaves attached to the leafy stem. The terminal velocity, however, slightly increased as the length of the leafy stems increased.

• Earthquakes and Structures
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• 제1권2호
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• pp.163-175
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• 2010

The vertical axis through the modal center of rigidity (m-CR) is used for interpreting the code torsional provisions in the design of eccentric multi-story building structures. The concept of m-CR has been demonstrated by the author in an earlier paper and the particular feature of this point is that when the vertical line of the centers of mass at the floor levels is passing through m-CR, minimum base torsion is developed. For this reason the aforesaid axis is used as reference axis for implementing the code provisions required by the equivalent static analysis. The study examines uniform mixed-bent-type multistory buildings with simple eccentricity, ranging from torsionally stiff to torsionally flexible systems. Using the results of a dynamic response spectrum analysis as a basis for comparisons, it is shown that the results of the code static design are on the safe side in torsionally stiff buildings, but unable to predict the required strength of bents on the stiff side of systems with a predominantly torsional response. Suggestions are made for improving the code provisions in such cases.

• Structural Engineering and Mechanics
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• 제61권1호
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• pp.15-29
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• 2017

The recently introduced index Ratio Of Torsion (ROT) quantifies the base shear amplification due to torsional effects on shear cantilever types of building structures. In this work, a theoretical proof based on the theory of elasticity is provided, depicting that the ratio of torsion (ROT) is independent of the forces acting on the structure, although its definition stems from the shear forces. This is a particular attribute of other design and evaluation criteria against torsion such as center of rigidity and center of strength. In the case of ROT, this evidence could be considered as inconsistent, as ROT is a function solely of the forces acting on structural members, nevertheless it is proven to be independent of them. As ROT is the amplification of the shear forces due to in-plan irregularities, this work depicts that this increase of internal shear forces rely only on the structural topology. Moreover, a numerical verification of this theoretical finding was accomplished, using linear statistics interpretation and nonlinear neural networks simulation for an adequate database of structures.

• Structural Engineering and Mechanics
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• 제46권4호
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• pp.519-531
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• 2013

To have a better understanding of the torsional mechanism and influencing factors of PC composite box-girder with corrugated steel webs, ultimate torsional strength of four specimens under pure torsion were analyzed with Model Test Method. Monotonic pure torsion acts on specimens by eccentric concentrated loading. The experimental results show that cracks form at an angle of $45^{\circ}$ to the member's longitudinal axis in the top and bottom concrete slabs. Longitudinal reinforcement located in the center of cross section contributes little to torsional capacity of the specimens. Torsional rigidity is proportional to shape parameter ${\eta}$ of corrugation and there is an increase in yielding torque and ultimate torque of specimens as the thickness of corrugated steel webs increases.

• Structural Engineering and Mechanics
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• 제66권5호
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• pp.637-648
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• 2018

When the centers of mass and stiffness of a building do not coincide, the structure experiences torsional responses. Such systems can consist of the underlying soil and the super-structure. The underlying soil may modify the earthquake input motion and change structural responses. Specific effects of the input motion shall also not be ignored. In this study, seismic demands of asymmetric buildings considering soil-structure interaction (SSI) under near-fault ground motions are evaluated. The building is modeled as an idealized single-story structure. The soil beneath the building is modeled by non-linear finite elements in the two states of loose and dense sands both compared with the fixed-base state. The infinite boundary conditions are modelled using viscous boundary elements. The effects of traditional and yield displacement-based (YDB) approaches of strength and stiffness distributions are considered on seismic demands. In the YDB approach, the stiffness considered in seismic design depends on the strength. The results show that the decrease in the base shear considering soft soil induced SSI when the YDB approach is assumed results only in the center of rigidity to control torsional responses. However, for fixed-base structures and those on dense soils both centers of strength and rigidity are controlling.

• 대한조선학회지
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• 제23권4호
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• pp.1-10
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• 1986

A container ship, due to wide hatch openings, has characteristics of poor torsional rigidity, strong coupling of horizontal-torsional modes and significant discontinuity in the longitudinal variation of hull sections. In the mathematical formulation of the problem the hull is modeled as a beam and the transfer matrix method is utilized. The cross decks between cargo hatch opening are separated from the main hull and regarded as equivalent springs restraining torsion of hull. The effect of shear deformation of ship-side plating on torsion is taken into account in addition to St. Venant's and bending torsional rigidities. Compatibility requirements at cross section discontinuity are approximately considered. Developing the practical calculation procedure and the computer programs for application to an actual ship, some parametric studies on modeling methods of the cross deck, the compatibility condition, added-mass center etc. are out for the purpose of comparison.