Nonlinear Dynamic Analysis Of 3-D Structure With Solid Elements And Its Damage Identification

Modal parameters as frequency are function of physical characters (mass, stiffness, damping ) of structure, when a damage appears, the physical characters of structure will change, and the modal parameter change subsequently. We can find out damage location and the damage level according to change of the modal parameter. This damage identification method according to vibration of structure is simple and convenient, it doesn't bring additional damage to structure. So this method is more and more accounted by people. So far, damage identification by artificial neural network is used in many domains.It needs to simulate every possible damaged state of structure when use the artificial neural network to detect damage of structure. The modal parameters under normal state and every possible damaged state is needed to train the neural network. So it's one of the key problem whether we can or can not simulate every state of structure accurately. The former structure analysis with shear model or bar system model are too rough to analyze accurately. Aiming at this disadvantage, solid element is used in finite element analysis in this paper. Hexahedron element with eight nodes is used for both concrete and steel. Concrete and steel are connected only by common node and have same displacement in common nodes. Steel and concrete's element stiffness matrix is calculated respectively, and collected to general stiffness matrix according to the common node displacement.Material's constitutive relation is a important factor to the finite element method. Nonlinear elastic increment constitutive model is used for concrete, and elastic-plasticity increment constitutive model is used for steel. In dynamic analysis, The author modify the existent equivalent uniaxial hysteretic model, a linear falling segment replaces the curve falling segment, and the unloading regulation in tension part is modified. The hysteretic model which is modified by the author is used to three-dimension structure analysis by equivalent strain method. A bilinear hysteretic model is used for steel, and the Baushinger effect is considered.According to the theory above, the author developed a program which can carry out modal analysis and linear and nonlinear time-history analysis on concrete and steel composed structures subjected to multi-directional seismic load. Then three examples is used to verify the program according to compare to the calculation result with SAP2000.As an application, a concrete frame with steel tube encased concrete columns subjected to seismic load is analyzed, six positions where will be damaged possibly under the earthquake are found out, nine damage levels is simulated in every position. All the data of fist seven damage levels at every damage position is imported to the artificial neural network(ANN) for learning and training by itself. Then other two damage levels is input to verify the neural network. It find that ANN has very good accuracy of damage identification.