Analysis Of Modal Synthesis Method For Large-scale Structural And Substructure Based Damage Detection Method

Along with increasingly widespread and application of health monitoring system on large-scale civil engineering structures, there are still some problems remain unresolved. For example, A finite element model with a certain accuracy will be needed when establishing a large-scale structural health monitoring systems for damage detection and health condition assessment. However, there will be problems such as too many unknown parameters, considerable computational effort, ill-conditioned resulting and slow convergence during model updating with large-scale structure. As a result, dynamic substructure method is analyzed and introduce to civil structure in this thesis, and then the dynamic substructure based damage detection method is proposed. The main contents are as follows:1. The free interface modal synthesis method and dual coordinate free interface modal synthesis method are both introduced to civil engineering structure. And in order to ensure a comprehensive precision for the application, appropriate modal intercept and substructure dividing principles are proposed for both modal synthesis method. It is observed that not only the geometry and material property, the result will be more accurate if also the inflection points were considered when dividing substructure.2. A long-span connected structure derives from a practical project is selected for numerical simulation. The results demonstrate the feasibility of applying the dynamic substructure methods to large-scale civil structure, as well as the correctness of proposed modal intercept standards and dividing principle. In addition, how the number of substructures influences the accuracy and computational efficiency are discussed.3. The dynamic substructure method is introduced to traditional finite element model updating method. First, the sensitivity matrix of frequency and mode shape with respect to elemental parameters using free interface modal synthesis method and dual coordinate free interface modal synthesis method. And dynamic substructure method based model updating method is established. Compared to the traditional method, the proposed substructure sensitivity method only need to calculate a relative small part of sensitivity matrix in each iteration step, and thus it will improve the computational efficiency greatly.4. A damage detection example is conducted on a frame structure using sensitivity model updating method derived from free interface modal synthesis method. The simulation results shows that compared to the traditional finite element model updating method, the proposed model updating approach based on the free interface modal synthesis method has a better stability of convergence and better ability to identify damage.5. The numerical examples on a frame structure confirm the effectiveness of the proposed model updating method derived from the dual coordinate free interface modal synthesis method. As this method only need to solve sensitivity matrix in certain substructure that have a small number of degrees of freedoms in each iteration step, and thus it will greatly reduce the iteration time. So it is expected that this method will be more suitable for large and complex structures with a large degree of freedoms and has great potential for practical applications.