• Earthquakes and Structures
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• 제8권4호
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• pp.843-857
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• 2015

System identification is regarded as the most basic technique for structural health monitoring to evaluate structural integrity. Although many system identification techniques extracting mode information (e.g., mode frequency and mode shape) have been proposed so far, it is also desired to identify physical parameters (e.g., stiffness and damping). As for high-rise buildings subjected to long-period ground motions, system identification for evaluating only the shear stiffness based on a shear model does not seem to be an appropriate solution to the system identification problem due to the influence of overall bending response. In this paper, a system identification algorithm using a shear-bending model developed in the previous paper is revised to identify both shear and bending stiffnesses. In this algorithm, an ARX (Auto-Regressive eXogenous) model corresponding to the transfer function for interstory accelerations is applied for identifying physical parameters. For the experimental verification of the proposed system identification framework, vibration tests for a 3-story steel mini-structure are conducted. The test structure is specifically designed to measure horizontal accelerations including both shear and bending responses. In order to obtain reliable results, system identification theories for two different inputs are investigated; (a) base input motion by a modal shaker, (b) unknown forced input on the top floor.

• Advances in concrete construction
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• 제1권1호
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• pp.1-27
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• 2013

Discrete steel fibres can increase significantly the bending and the shear resistance of concrete structural elements when Steel Fibre Reinforced Concrete (SFRC) is designed in such a way that fibre reinforcing mechanisms are optimized. To assess the fibre reinforcement effectiveness in shallow structural elements failing in bending and in shear, experimental and numerical research were performed. Uniaxial compression and bending tests were executed to derive the constitutive laws of the developed SFRC. Using a cross-section layered model and the material constitutive laws, the deformational behaviour of structural elements failing in bending was predicted from the moment-curvature relationship of the representative cross sections. To evaluate the influence of the percentage of fibres on the shear resistance of shallow structures, three point bending tests with shallow beams were performed. The applicability of the formulation proposed by RILEM TC 162-TDF for the prediction of the shear resistance of SFRC elements was evaluated. Inverse analysis was adopted to determine indirectly the values of the fracture mode I parameters of the developed SFRC. With these values, and using a softening diagram for modelling the crack shear softening behaviour, the response of the SFRC beams failing in shear was predicted.

• 한국해양공학회지
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• 제10권4호
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• pp.10-16
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• 1996

The vibration due to progressive ocean waves is analyzed for a typical footing-type offshore airport platform. The platform is modelled as a spring-supported Euler beam and buoyancy change due to wave is considered as excitation force, under the assumption that the wave propagates without distortion by the structure. The results show that the natural frequencies of this structure are distributed very closely and are little affected by boundary conditions and that the response charateristics due to ocean waves are quite different according to the wave frequency. In this study, the wave frequencies are divided into three regions; the resonance region at which the response is governed by the resonance between the natural mode at the wave frequency and the corresponding modal component of the wave excitation force, the bending governed region at which the response is governed by the bending stiffness, and the spring (buoyancy) governed region at which the response is governed by the spring constant ahd therefore is same as the incident wave form.

• 한국지반환경공학회 논문집
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• 제16권9호
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• pp.43-51
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• 2015

이 연구에서는 사실적인 매설관의 종방향 지진 응답특성을 규명하기 위하여 3차원 시간 이력해석이 가능한 쉘-스프링 수치모델을 구축하였으며 지진파 입사방향, 2방향 재하의 영향을 평가하였다. 조화운동을 적용한 결과, 이의 주기는 큰 영향을 주는 것으로 나타났다. 이는 주기가 감소할수록 매설관의 곡률이 증가하며 응답이 증가하기 때문인 것으로 판단된다. 입사방향의 영향을 평가하기 위하여 매설관 축 방향, 수평평면, 그리고 수직평면으로 운동을 재하 하였다. 매설관 축 방향으로 하중을 재하할 경우 휨 변형만을 유발하므로 응답이 매우 작게 계산되었다. 수평 및 수직평면에서 매설관 축 방향과 $45^{\circ}$로 재하 하는 경우 축방향 변위가 응답에 지배적인 영향을 주는 것으로 나타났다. 또한 2방향 재하 시, 휨 변형만을 유발하는 요소의 영향이 극히 작으므로 1방향으로만 재하 하는 경우와 결과가 유사하게 계산되었다. 계측기록을 재하 하는 경우에도 응답은 유사하게 계산되었고 1방향 및 2방향 해석의 결과는 크게 다르지 않은 것으로 나타났다. 결과적으로 매설관의 종방향 지진 응답은 축 방향 변위를 유발하는 1방향 재하만으로도 충분히 정확하게 예측할 수 있을 것으로 판단된다.

• Steel and Composite Structures
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• 제19권1호
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• pp.93-110
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• 2015

The thermomechanical bending response of anti-symmetric cross-ply composite plates is investigated by the use of the simple four variable sinusoidal plate theory. The theory accounts for sinusoidal distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations for the present theory is reduced, significantly facilitating engineering analysis. The validity of the present theory is demonstrated by comparison with solutions available in the literature. Numerical results are presented to demonstrate the behavior of the system. The influences of aspect ratio, side-to-thickness ratio, thermal expansion coefficients ratio and stacking sequence on the thermally induced response are studied. The present study is relevant to aerospace, chemical process and nuclear engineering structures which may be subjected to intense thermal loads.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.925-934
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• 2005

The dynamic response due to the unbalance and crack and the quasi-static response due to gravity are analytically derived based on the complex transfer matrix. The additional slope is expressed as function of the bending moment at crack position based on the fracture mechanics concept, and inversely the bending moment is expressed as function of the additional slope at the crack position. At each angle step during the shaft revolution, the additional slope and bending moment are calculated by an iterative method. The transient behavior is considered by introducing Fourier series expansion concept for the additional slope. Simulation is carried out for a simple rotor similar to those available in the literature and comparison of the basic crack behavior is shown. Using the additional slope, the cracked rotor behavior is explained with the crack depth increased: the magnitude of the additional slope increases and the closed crack duration during a revolution decreases as the crack depth increases. The direction of unbalance is also shown as a factor to affect the crack breathing. Whirl orbits are shown near the sub-critical speed ranges of the rotor.

• 한국소음진동공학회논문집
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• 제22권8호
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• pp.713-719
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• 2012

This paper deals with the natural frequency analysis and two experiments to evaluate first twisting and bending natural frequency of railway vehicle. The KS R 9228 testing method is generally performed as pseudo FRF(frequency response function) which is widely used by two accelerometers. The exciting method is utilized using the load weight(1 ton release). The modal testing is used to verify KS R 9228 testing result and the natural frequency analysis result. The first twisting and bending natural frequency should be above 10 Hz by resonance which is mostly generated between bogie and vehicle frame exciting low frequency. The first twisting and bending natural frequency of railway vehicle are successfully verified between analysis and test.

• Geomechanics and Engineering
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• 제22권1호
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• pp.65-80
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• 2020

This paper presents a theoretical investigation on the response of the thermo-mechanical bending of FG plate on variable elastic foundation. A quasi-3D higher shear deformation theory is used that contains undetermined integral forms and involves only four unknowns to derive. The FG plates are supposed simply supported with temperature-dependent material properties and subjected to nonlinear temperature rise. Various homogenization models are used to estimate the effective material properties such as temperature-dependent thermoelastic properties. Equations of motion are derived from the principle of virtual displacements and Navier's solution is used to solve the problem of simply supported plates. Numerical results for deflections and stresses of FG plate with temperature-dependent material properties are investigated. It can be concluded that the proposed theory is accurate and simple in solving the thermoelastic bending behavior of FG thick plates.

• 한국소음진동공학회논문집
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• 제15권10호
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• pp.1137-1147
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• 2005

The dynamic response due to the unbalance and crack and the quasi-static response due to gravity are analytically derived based on the complex transfer matrix. The additional slope is expressed as function of the bending moment at crack position based on the fracture mechanics concept, and inversely the bending moment is expressed as function of the additional slope at the crack Position. At each angle step during the shaft revolution, the additional slope and bending moment are calculated by an iterativemethod. The transient behavior is considered by introducing Fourier series expansion concept for the additional slope. Simulation is carried out for a simple rotor similar to those available in the literature and comparison of the basic crack behavior is shown. Using the additional slope, the cracked rotor behavior is explained with the crack depth increased: the magnitude of the additional slope increases and the closed crack duration during a revolution decreases as the crack depth increases. The direction of unbalance is also shown as a factor to affect the crack breathing. Whirl orbits are shown near the sub-critical speed ranges of the rotor.

• Steel and Composite Structures
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• 제37권5호
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• pp.533-549
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• 2020

Recently, Concrete-filled double skin steel tubular (CFDST) columns have proven an exceptional structural resistance in terms of strength, stiffness, and ductility. However, the resistance of these column members can be severely affected by the type of loading in which bending stresses increase in direct proportion with axial load and eccentricity value. This paper presents a non-linear finite element based modeling approach that studies the behavior of slender CFDST columns under biaxial loading. Finite element models were calibrated based on the outcomes of experimental work done by other researchers. Results from simulations of slender CFDST columns under axial loading eccentric in one direction showed good agreement with the experimental response. The calibrated models are expanded to a total of thirty models that studies the behavior of slender CFDST columns under combined compression and biaxial bending. The influences of parameters that are usually found in practice are taken into consideration in this paper, namely, eccentricity-to-diameter (e/D) ratios, slenderness ratios, diameter-to-thickness (D/t) ratios, and steel contribution ratios. Finally, an analytical study based on current code provisions is conducted. It is concluded that South African national standards (2011) provided the most accurate results contrasted with the Eurocode 4 (2004) and American Institute of Steel Construction (2016) that are found to be conservative. Accordingly, correction factors are proposed to the current design guidelines to provide more satisfactory results.