Papers by Keyword: Model Updating

Abstract: For the health monitoring of civil structures, the study of finite element model updating or damage detection mainly focuses on undamped systems. Thus, their objective has been exclusively restricted to the correction of the mass and stiffness matrices. In contrast, this paper performs the model updating and damage detection for damped structures. A theoretical contribution of this paper is to extend the cross-model cross-mode (CMCM) method to simultaneously update the mass, damping and stiffness matrices of a finite element model when only few spatially incomplete, complex-valued modes are available. Numerical studies are conducted for a five-story frame structure with multiple damaged elements. The numerical results reveal that applying the CMCM method, together with an iterative Guyan reduction scheme, can yield good damage detection in general.

Abstract: While rigid or pinned assumptions are adopted for steel frames in traditional modeling via finite element method, the actual behavior of the connections is usually neither. Semi-rigid joints enable connections to be modeled as partially restrained, which improves the quality of the model. To identify the connection stiffness and update the FE model, a newly-developed cross modal strain energy (CMSE) method is extended to incorporate the connection stiffness estimation. To illustrate the capability of the proposed parameter estimation and model updating algorithm, a four-story frame structure is demonstrated in the numerical studies. Several cases including Semi-rigid joint(s) on single connection and on multi-connections, are investigated. Numerical results indicate that an excellent updating is achievable and the connection stiffness can be estimated by CMSE method.

Abstract: The aim of updating models is to generate improved numerical models which may be applied in order to predict actual dynamic behaviors of the structure. The approach of numerical predictions to the behavior of a physical system is limited by the assumptions used in the development of the mathematical model. Model updating is about correcting invalid assumptions by processing vibration test results. Updating by improving the physical meaning of the model requires the application of considerable physical insight in the choice of parameters to update and the arrangement of constraints, force inputs and response measurements in the vibration test. The choice of updating parameters is the most important and the numerical predictions should be sensitive to small changes in the parameters. So methods used in model updating places a demand that the mass, stiffness and damping terms should be based on physically meaningful parameters. Using the structure frequency and local modal shape acquired from structural time-history responses, a model updating method of space grid structures was established in this paper. A numerical example is provided to prove the accuracy of this method. The results show that the method can be effectively used to correct the finite element model of space grid structures.

Abstract: In this paper, the concept and application of virtual prototype technology are simply introduced, and analyses the veracity program in course of complex multi-body system simulation. The rigid-flexible couple virtual prototype model of complex multi-body system including collision is built, and the veracity of virtual prototype simulation is evaluated combining limited test data. Updating some typical system parameters by sensitivity method and perturbation method, it makes the simulation results have better consistency with test results, and improves the simulation precision of virtual prototype model.

Abstract: A method for continuous box-girder bridge structure finite element (FE) model updating based on static-load testing is proposed. The procedure includes field static-load testing, FE modeling, FE model (parameter) updating, etc. Based on this procedure, the structure FE model updating for an expressway 5-span pre-stressed concrete continuous box-girder bridge is conducted. And the bridge structure static FE model, which is consistent with the static-load testing actual measure response, is gained. The updated FE model (parameter) is foundation of structural performance evaluation for the bridge.

Abstract: In the model updating process, the objective function is usually set as the weighted sum of the difference between analytical and experimental dynamic characteristics. But it is difficult to select the weighting factors since the relative importance of each parameter to updated results is not obvious but specific for different problem. To overcome this problem, multi-objective genetic algorithm (GA) is introduced into model updating by Gyeong-Ho Kim since there is no need for selecting weighting values in multi-objective optimization technique. To complex structures, however, it is difficult to update the structural models by GA because of the relative low efficiency. While Taguchi updating method, deemed as an efficient and robust method, is a good choice to update the models of large structures. But Taguchi method is only applied to solve the single objective optimization problem of model updating. Therefore, this paper proposed improved Taguchi updating method to deal with the problem of model updating using multi-objective optimization technique. Then the proposed method is applied to update the model of a 14-bay beam with measured frequencies and modal shapes. The updated results show that the proposed method is promising to structural model updating.

Abstract: The establishment of an effective finite element model (FEM) for the bridge structure is essential in the health monitoring system of urban grade separation bridge. It inevitably exist inconsistency of response between the FEM and practical structure due to various uncertain factors in the modeling and analysis procedure. Therefore the updating of FEM is necessary. A uniform design-based static model updating method is proposed in this paper, the allowable range of model parameters (the number is ) is divided into several levels (the number is ), the model updating method is transformed into a -factors and -levels test design. Several groups of combined parameters are selected to conduct test through finite element calculation based on the principle of uniform design method, and the optimal parameter group is obtained. This method is applied to the model updating of a complicated special-shaped urban grade separation bridge, and a perfect FEM with a good agreement with measured data is obtained. It confirms the feasibility and superiority of this method.

Abstract: According to the complex boundary condition of real bridge structure, appendix restraint parameters of structure boundary condition were detailed analyzed. The appendix horizontal and torsional restraint parameters were selected as research object. The least square constrained optimization inversion method was used to establish the question of reverse of bridge structure boundary appendix parameters based on tested and calculated mode parameters. The first order perturbation of eigen-value and eigen-vector based on matrix perturbation theory were substituted into the constrained optimization inversion equation, so the solving efficiency was improved greatly, and the iteration method was used to improve the precision. The corresponding program was made, and the example of a maglev railway girder shows that fairly well precise bridge structure boundary appendix parameters can be reserved with only former several modes parameters through four to seven times of iteration calculation.

Abstract: A metamodel can be represented by the forms of mathematical equations (response surface models) or neural networks (black-box models) in the interest of correlating the inputs (parameters) with the outputs (responses) of a physical system. In view of little relevant research, this paper attempts to use response surface models as surrogates for FE models due to the provision of explicit equations and easy implementation in the aspect of modeling updating. Metamodeling is achieved by using the design of experiment involving the 2k factorial design and the central composite design for parameter screening and structural input-response modeling respectively. The feasibility of the proposed method has been demonstrated using a numerical beam example which proves the satisfactory performance of employing such metamodels in model updating based damage identification.

Abstract: This paper makes a research on dynamic fingerprints methods and model updating methods of identification theories of bridge damage. And it has a full study on and makes a comparison among the four basic theories of dynamic fingerprints and their applications in engineering, signifying the advantages and disadvantages. The general procedures of damage identification of model updating method are proposed. And finally it points out that the problems needing further studies and the directions of development in damage identification theories.