Analysis Of Seismic Damage And Study On Damage Identification Of Steel Structures

Due to its light weight, high strength, excellent seismic performance, environmental protection and energy saving, etc, steel is widely used in industrial and civil construction. Particularly, with the improvement of seismic fortification standards and the confrontation of a more severely damage of the earthquake, steel structure will be one of the main building structure forms. In the meanwhile, various engineering accidents caused by accumulated damage of steel structure has also brought heavy losses in life and property, so it is of great significance to analysis the seismic damage and have a study on damage identification of steel structure after the disaster.The steel structure has a good dynamic performance, as people cannot totally understand its failure mechanism, the brittle failure still occurs to cyclic loading in earthquake. Based on the theory of continuum damage mechanics, a numerical model of the overall steel structure is built, and the process of the plastic development, damage onset and damage accumulation of the tall steel building are analyzed firstly under earthquake action. Taking the isotropic hardening and kinematic hardening into account, this model can truly reflect the characteristics of cyclic hardening after material yielding. To determine the onset of damage, numerical analysis data from ABAQUS and real experimental tensile data help to establish relations between the damage initial strain and stress triaxiality. The damage evolution law is defined as the function of the plastic displacement, which can effectively reduce the dependence of the calculation results on the finite element mesh after the damage. The ABAQUS numerical analysis of a 9-story steel frame structure shows the basiclly consistency of the identification results and the actual damage, furthermore, parameters of this model are easy to obtain and more convenient to practical application.For vibration-based damage identification, dynamic testing is only limited to a few measurement points, data error, and model error are difficult to avoid. In order to identify the local damage of complex structure effectively, the modal participation factor is introduced to form complete mode shapes to avoid the additional errors with model reduction or extended method, and a nonlinear damage control equations are established. By modified Gauss Newton least squares means and singular value decomposition, the damage control equations are solved to get the damage parameters. In view of present situation, a two-stage damage identification method based on optimal measurement points is put forward. The first stage is the optimization of measurement points, putting some sensors at accessible site throughout the structure, with the help of identification results, the rough damage areas almost come into being, consequently, the optimal one which is closest to the rough damage areas can be found. In the second stage, rearranging sensors on the identified optimal measurement points, therefore test data will include more damage information, and can accurately identify damage location and severity of the components. The numerical results of the damage identification of a 3-story steel frame show that the first stage result may detect the optimal measurement points under any damage cases, proper measuring data in the second stage can identify the locations and the degree of damage accurately. This method has high anti-noise ability and fault tolerance.Based on the limited testing information, the damage model is established to study the problems of damage identification of the spatial steel structures. Most methods are generally define the damage by reduction the elastic modulus of the overall bar, which cannot characterize specific parts of the damage state, and hardly achieve effective identification of local damage. For the purpose of characterizing joint and cross damage, the element stiffness matrix is decomposed into axial stiffness, torsional stiffness and bending stiffness of integration points. Defining the damage parameters in the element level, the numerical simulation of a 4-story steel frame structure shows the proposed way which cannot only locate the damage of the spatial structure accurately, but also effectively assess the damage extent.There are many deficiencies in seismic appraisal code and appraiser methods, which can hardly satisfy the practical usage of engineering. For this reason, the seismic performance assessment method of steel structure based on damage is proposed. Damage value of components and the overall structure are taken as the damage index, the seismic damage value of the components is caculated by the damage model directly mentioned in Chapter Two. To get the floor damage value, it is necessary to measure structural model parameters, and then calculated by the layer damage model, while the damage value of the whole structure can be obtained from the weighted damage value of the components or floors. According to performance objectives of owners and the calculation of damage value to the components and structure, the seismic performance of the 9-story steel building is reasonably evaluated.