• Earthquakes and Structures
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• 제7권4호
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• pp.415-448
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• 2014

A method is presented in this paper to analyze the dynamic response behavior of suspended building structures. The effect of semi-rigid connections that link suspended floors with their supporting structure on structural performance is investigated. The connections, like the restrains in non-structural suspended components, are designed as semi-rigid to avoid pounding and as energy dissipation components to reduce structural response. Parametric study is conducted to assess the dynamic characteristics of suspended building structures with varying connection stiffness and suspended mass ratios. Modal analysis is applied to identify the two distinct sets of vibration modes, pendulum and bearing, of a suspended building structure. The cumulative modal mass is discussed to ensure the accuracy in applying the method of response spectrum analysis by SRSS or CQC modal combination. Case studies indicate that a suspended building having semi-rigid connections and proper suspended mass ratios can avoid local pounding failure and reduce seismic response.

• 한국소음진동공학회논문집
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• 제17권3호
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• pp.257-263
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• 2007

Detection of structural damage is an inverse problem in structural engineering. There are three main questions in the damage detection: existence, location and extent of the damage. In concept, the natural frequency and mode shapes of any structure must satisfy an eigenvalue problem. But, if a potential damage exists in a structure, an error resulting from the substitution of the refined analytical finite element model and measured modal data into the structural eigenvalue equation will occur, which is called the residual modal forces, and can be used as an indicator of potential damage in a structure. In this study, a useful damage detection method is proposed and compared with other two methods. Two degree-of-freedom system and Cantilever beam are used to demonstrate the approach. And the results of three introduced method are compared.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.1000-1004
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• 1995

In the case of the external cylindrical grinding machine, the grinding mechanism can cause a wheel to vibrate due to a wheel cutter. This phenomena will bring about the unsymmetric wear up to high frequency without any relation of rotational speed. So far, when the grinding spindle is analyzed, it is assumed that a wheel is considered as lumped mass at the endof a beam. Nowadays, there is a tendency to use the wheel with a lsrge diameter or CBN wheel to achieve the high speed and accuracy grinding performance. Therefore, this kind of assumption is no longer valid. At the analysis of the grinding spindle, the parameter which dapends on the dynamic characteristics is a combination force between each part. For example, there is the tightness torque of a bolt and taper element in the grindle. In addition, the material property of the wheel can contribute the dynamic characteristics. This paper shows the mode participation of the shell mode of the wheel in the grindle and the dynamic characteristics according to the parameters which are the configuration of the flange and tightness torque of a bolt and taper. Modal parameter of the wheel, flange and the spindle can be extracted through frequency response function obtained by modal test. After that, by changing the tightness torque and kinds of wheel, we could accomplish the test in the whole combined grinding spindle. To perform modal analysis of vibration characteristics in the grinding spindle, we could develop the model of finite element method.

• Structural Engineering and Mechanics
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• 제39권5호
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• pp.703-716
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• 2011

The accurate dynamic analysis of structures is usually performed by a fine finite element discretization with very large number of degrees of freedom. Apart from modal analysis, one can reduce the number of final equations by assuming the deformed shape of the structure as a linear combination of independent Ritz vectors. The efficiency of this method relies heavily on the vectors selected. In this paper, a new set of Ritz vectors is proposed. It is primarily proved that these vectors are linearly independent. Subsequently, various two and three-dimensional examples are analyzed based on the proposed method. In each case, the results are compared with the ones obtained based on usual Ritz and modal analysis methods. It is finally concluded that the proposed method is very effective and efficient method for dynamic analysis of structures in frequency domain.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.555-574
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• 2023

An efficient optimization algorithm and damage-sensitive objective function are two main components in optimization-based Finite Element Model Updating (FEMU). A suitable combination of these components can considerably affect damage detection accuracy. In this study, a new hybrid damage-sensitive objective function is proposed based on combining two different objection functions to detect the location and extent of damage in structures. The first one is based on Generalized Pseudo Modal Strain Energy (GPMSE), and the second is based on the element's Generalized Flexibility Matrix (GFM). Four well-known population-based metaheuristic algorithms are used to solve the problem and report the optimal solution as damage detection results. These algorithms consist of Cuckoo Search (CS), Teaching-Learning-Based Optimization (TLBO), Moth Flame Optimization (MFO), and Jaya. Three numerical examples and one experimental study are studied to illustrate the capability of the proposed method. The performance of the considered metaheuristics is also compared with each other to choose the most suitable optimizer in structural damage detection. The numerical examinations on truss and frame structures with considering the effects of measurement noise and availability of only the first few vibrating modes reveal the good performance of the proposed technique in identifying damage locations and their severities. Experimental examinations on a six-story shear building structure tested on a shake table also indicate that this method can be considered as a suitable technique for damage assessment of shear building structures.

• Steel and Composite Structures
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• 제42권5호
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• pp.685-697
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• 2022

In this paper, a vibration-based method using the change ratios of modal data and the experience-based learning algorithm is presented for quantifying the position, size, and interface layer of delamination in laminated composites. Three types of objective functions are examined and compared, including the ones using frequency changes only, mode shape changes only, and their combination. A fine three-dimensional FE model with constraint equations is utilized to extract modal data. A series of numerical experiments is carried out on an eight-layer quasi-isotropic symmetric (0/-45/45/90)s composited beam for investigating the influence of the objective function, the number of modal data, the noise level, and the optimization algorithms. Numerical results confirm that the frequency-and-mode-shape-changes-based technique yields excellent results in all the three delamination variables of the composites and the addition of mode shape information greatly improves the accuracy of interface layer prediction. Moreover, the EBL outperforms the other three state-of-the-art optimization algorithms for vibration-based delamination detection of composites. A laboratory test on six CFRP beams validates the frequency-and-mode-shape-changes-based technique and confirms again its superiority for delamination detection of composites.

• Structural Engineering and Mechanics
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• 제87권1호
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• pp.57-68
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• 2023

Response spectrum method is still an effective approach for the design of buildings with supplemental dampers. In practice, complex complete quadratic combination (CCQC) rule is always used in the response spectrum method to consider the effect of non-classical damping. The conventional CCQC rule is based on exact complex mode vectors. Sometimes the calculated complex mode vectors may be not excited by the external loading and errors in the structural responses always arise due to the mode truncation. Load-dependent Ritz (LDR) vectors are associated with the external loading and LDR vectors not excited can be automatically excluded. Also, contributions of higher modes are implicitly contained in the LDR vectors in terms of static responses. To improve the calculation efficiency and accuracy, LDR vectors are introduced in the CCQC rule in the present study. Firstly, the generation procedure of LDR vectors suitable for non-classical damping system is presented. Compared to the conventional LDR vectors, the LDR vectors herein are complex-valued and named as complex LDR (CLDR) vectors. Based on the CLDR vectors, the CCQC rule is then rederived and an improved response spectrum method is developed. Finally, the effectiveness of the proposed method in this paper is verified through three typical non-classical damping buildings. Numerical results show that the CLDR vector is superior to the complex mode with the same number in the calculation. Since the generation of CLDR vectors requires less computational cost and storage space, the method proposed in this paper offers an attractive alternative, especially for structures with a large number of degrees of freedom.

• 한국지진공학회논문집
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• 제14권2호
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• pp.75-84
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• 2010

원자력발전소에 설치되는 주요 전기기기들의 내부 부품을 내진검증하기 위해서는 캐비닛내부응답스펙트럼이 필요하고, 이는 캐비닛의 각 위치에서 정확한 지진응답을 구한 후에 생성이 가능하다. 반면에 대부분의 전기기기는 질량과 강성 분포가 복잡하기 때문에 해석적 방법에 의해 동적 분석을 수행하는 것이 어렵다. 이러한 여건을 감안하여 이 연구에서는 해석과 시험을 조합하여 기기의 지진응답을 예측하는 간편한 절차를 제안하였다. 제안된 절차는 먼저 충격시험을 통하여 규명된 실험모드특성을 이용하여 독립된 모드방정식을 구성하고, 이로부터 모드응답을 계산한 다음, 각 모드응답을 중첩함으로써 구조물의 지진응답을 예측한다. 제안된 절차의 신뢰성을 검증하기 위해서, 별도로 제작된 단순 강재 프레임 시편에 제안된 절차를 적용하여 지진응답을 예측하고, 이를 실제 진동대시험을 통하여 계측한 결과와 비교하였다. 이 연구를 통하여 충격시험에 의해 얻어진 실험모드특성을 이용하여 구조물의 지진응답을 비교적 정확하게 예측할 수 있음을 확인하였다.

• Smart Structures and Systems
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• 제25권1호
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• pp.1-22
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• 2020

The modal strain energy method is one of the efficient methods for detecting damage in the structures. Due to existing some limitations in real-world structures, sensors can only be located on a limited number of degrees of freedom (DOFs) of a structure. Therefore, the mode shape values in all DOFs of structures cannot be measured. In this paper, a modified modal strain energy based index (MMSEBI) is introduced to locate damaged elements of structures when a limited number of sensors are used. The proposed MMSEBI is based on the reconstruction of mode shapes using Improved Reduction System (IRS) method. Therefore, in the first step by employing IRS method, mode shapes in slave degrees of freedom are estimated by those of master degrees of freedom. In the second step, the proposed MMSEBI is used to located damage elements. In order to evaluate the efficiency of the proposed method, two numerical examples are considered under different damage patterns considering the measurement noise. Moreover, the universal threshold based on statistical hypothesis testing principles is applied to damage index values. The results show the effectiveness of the proposed MMSEBI for the structural damage localization when comparing with the available damage index named MESBI. The results demonstrate that the presented method can be used as a practical strategy for structural damage identification, especially when a limited number of sensors are installed on the structure. Finally, the combination of MMSEBI and IRS method can provide a reliable tool to identify the location of damage accurately.

• 소음진동
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• 제10권5호
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• pp.843-848
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• 2000

BEA(Boundary Element Analysis) based on Kirchhoff-Helmholtz integral equation is widely used in the prediction of sound radiation problems of vibrating structures. Accurate estimation of sound pressure distribution by BEA can be [possible if and only if dynamic behavior of the relating structure was described correctly. Another plausible method of sound radiation phenomena could be the NAH(Nearfield Acoustic Holography) method. NAH also based on the identical governing equation with BEA could be one of the best acoustic imaging schemes but it has disadvantages of the complexity of measurement and of the need of large amount of measuring points. In this paper, modal expansion method is presented for taking accurate dynamic data of the structures efficiently. This method makes use of vibration principle an arbitrary dynamic behavior of the structure is described by the summation of that structures mode shapes which can be calculated by FEA easily and accurately. Sound pressure field from a vibration flat plate is calculated using the combination of vibration signal on that flat plate from experiment, and of the natural mode shapes form FEA. When sound pressure field from vibration signal is calculated the importance of the phase information was emphasized.