• Computational Structural Engineering : An International Journal
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• v.3 no.1
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• pp.1-7
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• 2003

For system identification of large structures, it is not practical to identify the entire structure due to the prohibitive computational time and difficulty in numerical convergence. This paper explores the possibility of performing system identification at substructure level, taking advantage of reduction in both the number of unknowns and the number of degrees of freedom involved. Another advantage is that different portions (substructures) of a structural system can be identified independently and even concurrently with parallel computing. Two substructural identification methods are formulated on the basis whether substructural approach is used to obtain first-order or second-order model. For substructural first-order model, identification at the substructure level will be performed by means of the Observer/Kalman filter Identification (OKID) and the Eigensystem Realization Algorithm (ERA) whereas identification at the global level will be performed to obtain second-order model in order to evaluate the system's stiffness and mass parameters. In the case of substructural second-order model, identification will be performed at the substructure level throughout the identification process. The efficiency of the proposed technique is shown by numerical examples for multi-storey shear buildings subjected to random forces, taking into consideration the effects of noisy measurement data. The results indicate that both the proposed methods are effective and efficient for damage identification of large structures.

• Structural Engineering and Mechanics
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• v.67 no.4
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• pp.359-368
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• 2018

In this paper, a method is presented to identify the physical and modal parameters of multistory shear building based on substructural technique using block pulse generalized operational matrix and genetic algorithm. The substructure approach divides a complete structure into several substructures in order to significantly reduce the number of unknown parameters for each substructure so that identification processes can be independently conducted on each substructure. Block pulse functions are set of orthogonal functions that have been used in recent years as useful tools in signal characterization. Assuming that the input-outputs data of the system are known, their original BP coefficients can be calculated using numerical method. By using generalized BP operational matrices, substructural dynamic vibration equations can be converted into algebraic equations and based on BP coefficient for each story can be estimated. A cost function can be defined for each story based on original and estimated BP coefficients and physical parameters such as mass, stiffness and damping can be obtained by minimizing cost functions with genetic algorithm. Then, the modal parameters can be computed based on physical parameters. This method does not require that all floors are equipped with sensor simultaneously. To prove the validity, numerical simulation of a shear building excited by two different normally distributed random signals is presented. To evaluate the noise effect, measurement random white noise is added to the noise-free structural responses. The results reveal the proposed method can be beneficial in structural identification with less computational expenses and high accuracy.

• Structural Engineering and Mechanics
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• v.61 no.6
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• pp.807-816
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• 2017

In this paper, we introduce an efficient new model reduction method, named the automated static condensation method, which is developed for the local analysis of large finite element models. The algebraic multilevel substructuring procedure is modified appropriately, and then applied to the original static condensation method. The retained substructure, which is the local finite element model to be analyzed, is defined, and then the remaining part of the global model is automatically partitioned into many omitted substructures in an algebraic perspective. For an efficient condensation procedure, a substructural tree diagram and substructural sets are established. Using these, the omitted substructures are sequentially condensed into the retained substructure to construct the reduced model. Using several large practical engineering problems, the performance of the proposed method is demonstrated in terms of its solution accuracy and computational efficiency, compared to the original static condensation method and the superelement technique.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.2
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• pp.132-151
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• 1993

The proposed method in this paper. termed the substructural reanalysis technique, utilizes the computational merits of the component mode synthesis technique and of reanalysis technique for the design sensitivities of the dynamic characteristics of substructurally combined structure. It is shown that the dynamic characteristics of the entire structure can be obtained by synthesizing the substructural eigensolution and the characteristics of the eigensolution for the design variables of the modifiable substructure. In this paper , the characteristics of the eigenvalue problems obtained by this proposed method are compared to exact eigensolution in terms of accuracy and computational efficiency. and the advantage of this proposed method as compared to the direct application of the whole structure and experimental results is demonstrated through examples of numerical calculation for the dynamic characteristics (natural frequencies and mode shapes) of a flexible vibration of thin cylinderical shell with branch shell under 2-end fixed positions, boundary condition. Thin cylinderical shell of overall length 1280mm, external diameter 360mm, thickness 3mm with branch shell is made of mild steel. The load condition for dynamic response in this paper is impulsive load of which magnitude is 10kgf, which have short duration of 0.1 sec. and time interval applied to calculate. $\Delta$T is 1.0$\times$10 super(-4) seconds.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.184-191
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• 1997

A method, termed as the substructural sensitivity synthesis method, which utilizes the computational merits of the component mode synthesis technique is proposed to calculate design sensitivity of modal parameters of substructurally combined structures. In this method, the sensitivity analysis is combined with component mode synthesis thchnique. thus the degrees of freedom of a combined structure can be dramatically reduced. Free-interface mode method including the residual attachment modes among the component mode synthesis methods is used to calculate the modal sensitivity of the combined structure. For the design sensitivities of modal properties of structure, the Nelson's method, which is exact solving method is used. It is shown that the modal sensitivities of the entire structure can be obtained by synthesizing the substructural modal data, and the sensitivities of the modal data about the design variables of modifiable substructure. Using the proposed method, the final degrees of freedom of entire structure can be remarkably reduced to calculate the modal parameter sensitivities. With a structure composed of beams and plates, as an example, the sensitivities of the eigenvalues and eigenvectors obtained by this proposed method were compared with the exact solutions in terms of accuracy.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.140-149
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• 1992

The new method, termed the substructural eigensensitivity synthesis method, utilizes the computational merits of the component mode synthesis technique and of sensitivity analysis for the design sensitivities of the dynamic characteristics of substructurally combined structures. It is shown that the eigensensitivities of the entire structure can be obtained by synthesizing the substructural eigensolution and the sensitivities of the eigensolution for the design variables of the modifiable substructure. The sensitivities of the eigenvalues and eigenvectors obtained by the new method are compared to exact eigensolutions in terms of accuracy and computational efficiency. The small errors in eigensensitivity due to the truncation of higher modes remain within a manageable and permissible range for further analysis. The advantage of the newly proposed method as compared to the direct application of sensitivity analysis of the whole structure is demonstrated through examples.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.3
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• pp.9-20
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• 1999

A method is proposed to estimate the joint damages of a steel structure from modal data using the neural networks technique. The beam-to-column connection in a steel frame structure is represented by a zero-length rotational spring of the end of the beam element, and the connection fixity factor is defined based on the rotational stiffness so that the factor may be in the range 0~1.0. Then, the severity of joint damage is defined as the reduction ratio of the connection fixity factor. Several advanced techniques are employed to develop the robust damage identification technique using neural networks. The concept of the substructural indentification is used for the localized damage assessment in the large structure. The noise-injection learning algorithm is used to reduce the effects of the noise in the modal data. The data perturbation scheme is also employed to assess the confidence in the estimated damages based on a few sets of actual measurement data. The feasibility of the proposed method is examined through a numerical simulation study on a 2-bay 10-story structure and an experimental study on a 2-story structure. It has been found that the joint damages can be reasonably estimated even for the case where the measured modal vectors are limited to a localized substructure and the data are severely corrupted with noise.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.543-553
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• 2004

This paper covered two related subjects: the use of the inverse modal perturbation technique to assess structural damage in existing structures; and the use of a seismic capacity evaluation to assess damaged structures, with the aid of the identified structural damage. The substructural identification and the Tikhonov regularization algorithm were incorporated for efficient damage assessment of complex and large frame structures. The seismic capacity of a damaged structure was evaluated by comparing the structure's seismic responses and seismic damage indices. The effectiveness of the proposed method has been investigated through the numerical simulation study for a twenty-story frame structure with undamaged and damaged cases, and also different earthquake excitations.

• Korean Journal of Construction Engineering and Management
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• v.6 no.1 s.23
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• pp.125-132
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• 2005

Domestic construction firms make every effort to save cost and, contrarily, enhance quality for competitive advantage in the market. Structural work of building construction takes chaise of the total cost and schedule, thus elaborate planning and management of the work help to lead the project into a successful way. Therefore, the idea to save time and cost and enhance constructability securing quality and safety of the work should be developed after analyzing the designed documents and site conditions comprehensively in the initial construction planning phase. Value Engineering (VE) technique is introduced in the substructural work in this paper to save cost creatively and systematically in the design and construction phase. A practical VE model that is applied to the underground building work systematically is proposed to save cost and it applies to the actual project to confirm the effectiveness of the model.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.3
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• pp.116-126
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• 1993

The finite element method(FEM) has been commonly used for structural dynamic analysis. However, the direct global application of FEM to large complex structures such as ships and offshore structures requires considerable computational efforts, and remarkably more in structural dynamic optimization problems. Adoption of the component-mode synthesis method is an efficient means to overcome the above difficulty. Among three classes of the component-mode synthesis method, the free-interface mode method is recognized to have the advantages of better computational efficiency and easier implementation of substructures' experimental results, but the disadvantage of lower accuracy in analytical results. In this paper, an advanced method to improve the accuracy in the application of the free-interface mode method for the vibration analysis of large complex structures is presented. In order to compensate the truncation effect of the higher modes of substructures in the synthesis process, both residual inertia and stiffness effects are taken into account and a frequency shifting technique is introduced in the formulation of the residual compliance of substructures. The introduction of the frequency shrift ins not only excludes cumbersome manipulation of singular matrices for semi-definite substructural systems but gives more accurate results around the specified shifting frequency. Numerical examples of typical structural models including a ship-like two dimensional finite element model show that the analysis results based on the presented method are well competitive in accuracy with those obtained by the direst global FEM analysis for the frequencies which are lower than the highest one employed in the synthesis with remarkably higher computational efficiency and that the presented method is more efficient and accurate than the fixed-interface mode method.