• 한국강구조학회 논문집
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• 제25권2호
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• pp.165-178
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• 2013

이 논문에는 정모멘트를 받는 강합성거더의 공칭휨강도를 평가하기 위한 연구를 수록하였다. 한계상태설계법을 적용한 현행 도로교설계기준(2012)에 제시된 합성거더의 휨강도 규정은 국내에서 생산되는 일반구조용 강재를 사용한 합성거더에 적용할 수 있다. 고성능 강재 HSB600뿐만 아니라 HSB800를 적용한 강합성거더에 적용하기 위해서는 현행 공칭휨강도 평가식을 개선해야될 필요성이 있다. 강합성거더의 공칭휨강도를 평가하기 위하여, 기존에 수행된 연구들을 고찰하였으며 모멘트-곡률해석방법을 이용하여 다양한 단면을 갖는 강합성거더의 극한휨강도와 연성비를 평가하기 위한 변수해석을 수행하였다. 변수해석결과를 토대로 일반강재를 적용한 강합성거더에 대해 기존 평가식보다 덜 보수적인 공칭휨강도 평가식을 제안하였다. 또한 고성능 강재 HSB600과 HSB800을 적용한 강합성거더의 새로운 공칭휨강도 평가식도 함께 제안하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.394-400
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• 2008

This paper presents an analytical method to investigate the stability of FDBs (fluid dynamic bearings) considering the tilting motion. The perturbed equations of motion are derived with respect to translational and tilting motion for the general rotor-bearing system with five degrees of freedom. The Reynolds equations and their perturbed equations are solved by using the FEM in order to calculate the pressure, load capacity, and the stiffness and damping coefficients. This research introduces the radius of gyration to the equations of notion in order to express the mass moment of interia with respect to the critical mass. Then the critical mass of FDBs is determined by solving the eigenvalue problem of the linear equations of motion. This research is numerically validated by comparing the stability chart of FDBs with the time response of the whirl radius obtained from the direct integration of the equations of motion. This research shows that the tilting motion is one of the major design considerations to determine the stability of rotating system. It also shows that the stability of FDBs considering only translation is overestimated in comparison with the stability of FDBs considering both translational and tilting motion.

• 한국압력기기공학회 논문집
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• 제15권2호
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• pp.71-80
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• 2019

In this study, limit load equations of thick-walled pipes with inner and outer circumferential surface cracks were derived based on force and moment equilibrium conditions. Since the limit load equations based on the mean radius at uncracked ligament, previously proposed by Kanninen et al., are based on the premise that the pipe wall thickness is relatively thin, the existing limit load solutions are only applicable to thin-walled pipes. In order to analyze the effect of the pipe thickness and surface crack depth on the limit load results, the predictions using the present limit load equations are compared with those using the existing solutions for thin-walled pipes. Being derived considering the thickness effect, the limit load solutions from this paper are believed to be more accurate for thick-walled pipes than the limit load equations presented for thin-walled pipes, and thus to be valuable equations for integrity assessment of thick-walled pipes.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1986년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 17-18 Oct. 1986
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• pp.251-255
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• 1986

Some missiles using canards as control device adopt rollerons to reduce roll motion due to aerodynamically induced rolling moment. This paper presents equations of motion of these missiles including the gyroscopic effect of rolleron rotors. Some linearized analysis results and simulation results are shown to coincide, thus some characteristic motions of missiles and rollerons can be seen.

• Smart Structures and Systems
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• 제23권6호
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• pp.641-651
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• 2019

The stochastic stability control of the parameter-excited vibration of an inclined stay cable with multiple modes coupling under random and periodic combined support disturbances is studied by using the direct eigenvalue analysis approach based on the response moment stability, Floquet theorem, Fourier series and matrix eigenvalue analysis. The differential equation with time-varying parameters for the transverse vibration of the inclined cable with control under random and deterministic support disturbances is derived and converted into the randomly and deterministically parameter-excited multi-degree-of-freedom vibration equations. As the stochastic stability of the parameter-excited vibration is mainly determined by the characteristics of perturbation moment, the differential equation with only deterministic parameters for the perturbation second moment is derived based on the $It{\hat{o}}$ stochastic differential rule. The stochastically and deterministically parameter-excited vibration stability is then determined by the deterministic parameter-varying response moment stability. Based on the Floquet theorem, expanding the periodic parameters of the perturbation moment equation and the periodic component of the characteristic perturbation moment expression into the Fourier series yields the eigenvalue equation which determines the perturbation moment behavior. Thus the stochastic stability of the parameter-excited cable vibration under the random and periodic combined support disturbances is determined directly by the matrix eigenvalues. The direct eigenvalue analysis approach is applicable to the stochastic stability of the control cable with multiple modes coupling under various periodic and/or random support disturbances. Numerical results illustrate that the multiple cable modes need to be considered for the stochastic stability of the parameter-excited cable vibration under the random and periodic support disturbances, and the increase of the control damping rather than control stiffness can greatly enhance the stochastic stability of the parameter-excited cable vibration including the frequency width increase of the periodic disturbance and the critical value increase of the random disturbance amplitude.

• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.99-116
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• 2014

The American Concrete Institute (ACI) 318-11 permits the use of the moment magnifier method for computing the design ultimate strength of slender reinforced concrete columns that are part of braced frames. This computed strength is influenced by the column effective length factor K, the equivalent uniform bending moment diagram factor $C_m$ and the effective flexural stiffness EI among other factors. For this study, 2,960 simple braced frames subjected to short-term loads were simulated to investigate the effect of using different methods of calculating the effective length factor K when computing the strength of columns in these frames. The theoretically computed column ultimate strengths were compared to the ultimate strengths of the same columns computed from the ACI moment magnifier method using different combinations of equations for K and EI. This study shows that for computing the column ultimate strength, the current practice of using the Jackson-Moreland Alignment Chart is the most accurate method for determining the effective length factor. The study also shows that for computing the column ultimate strength, the accuracy of the moment magnifier method can be further improved by replacing the current ACI equation for EI with a nonlinear equation for EI that includes variables affecting the column stiffness and proposed in an earlier investigation.

• Advances in concrete construction
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• 제9권1호
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• pp.23-31
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• 2020

Geometric nonlinearity can significantly affect load-carrying capacity of slender columns. Dependence of structural stability on columns necessitates the consideration of second-order effects in the design process of columns, appropriately. On the whole, the design codes present a simplified procedure for second order analysis of slender columns. In this approximate method, the end moments of columns resulted from linear analysis (first-order) are multiplied by the recommended moment amplification factors of codes to achieve magnified moments of the second-order analysis. In the other approach, the equilibrium equations are directly solved for the deformed configuration of structure, so the resulting moments and deflections contain the influence of slenderness and increase more rapidly than do loads. The aim of this study is to evaluate the accuracy of moment amplification factors of Iranian national building code whose provisions are similar to the ACI requirement. Herein, finite element method is used to achieve magnified end moments of reinforced concrete moment resisting frames, and the outcomes are compared with the moments acquired based on the proposed approximate method by Iranian national building code. The results show that the approximate method of Iranian code for calculating magnified moments has significant errors for both unbraced and braced columns.

• Smart Structures and Systems
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• 제18권6호
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• pp.1233-1250
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• 2016

Cracks in plate-like structures are some of the main reasons for destruction of the entire structure. In this study, a novel two-stage methodology is proposed for damage detection of flexural plates using an optimized artificial neural network. In the first stage, location of damages in plates is investigated using curvature-moment and curvature-moment derivative concepts. After detecting the damaged areas, the equations for damage severity detection are solved via Bat Algorithm (BA). In the second stage, in order to efficiently reduce the computational cost of model updating during the optimization process of damage severity detection, multiple damage location assurance criterion index based on the frequency change vector of structures are evaluated using properly trained cascade feed-forward neural network (CFNN) as a surrogate model. In order to achieve the most generalized neural network as a surrogate model, its structure is optimized using binary version of BA. To validate this proposed solution method, two examples are presented. The results indicate that after determining the damage location based on curvature-moment derivative concept, the proposed solution method for damage severity detection leads to significant reduction of computational time compared with direct finite element method. Furthermore, integrating BA with the efficient approximation mechanism of finite element model, maintains the acceptable accuracy of damage severity detection.

• Earthquakes and Structures
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• 제15권3호
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• pp.243-251
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• 2018

The dynamic responses of a rocking wall-moment frame (RWMF) with a post-tensioned cable are investigated. The nonlinear equations of motions are developed, which can be categorized as a single-degree-of-freedom (SDOF) model. The model is validated through comparison of the rocking response of the rigid rocking wall (RRW) and displacement of the moment frame (MF) against that obtained from Finite Element analysis when subjected ground motion excitation. A comprehensive parametric analysis is carried out to determine the seismic performance factors of the RWMF systems under near-fault trigonometric pulse excitation. The horizontal displacement of the RWMF system is compared with that of MF structures without RRW, revealing the damping effect of the RRW. Frame displacement spectra excited by trigonometric pulses and recorded earthquake ground motions are constructed. The effects of pulse type, mass ratio, frame stiffness, and wall slenderness variations on the displacement spectra are presented. The paper shows that the coupling with a RRW has mixed results on suppressing the maximum displacement response of the frame.

• 한국강구조학회 논문집
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• 제11권2호통권39호
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• pp.131-142
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• 1999

뒤틀림 효과를 고려한 곡선보의 일반적 거동은 Vlasov에 의해 제시된 미분 방정식으로 표시된다. 일반적으로 거더의 단면을 결정하는데 가장 큰 영향을 미치는 요인은 휨모멘트이다. 곡선 교량 계획시 곡선격자형교의 단면을 쉽게 가정하기 위해서 본 논문에서는 직선거더와 곡선거더의 휨모멘트비를 제시하였다. 이 비는 중심각 ${\theta}(L/R)$를 변수로 하여 근사식으로 나타내었다. 이 휨모멘트 근사식과 제시된 영향선은 3경간 곡선격자형교를 보다 쉽게 설계하는데 이용될 수 있다.