Parameter Identification Experiment And Research On Elastic Foundation Slab And Reinforced Concrete Frame Structure

In these two decades, extensive attention has been focused on the researches about structural damage identification based on dynamic information, the studies in this field have been widely conducted by the scholars. Due to the complexity of civil engineering structures, many key factors are neglected in structural modeling, such as the influence of the soil-structure dynamic interaction is not considered. The lower modes are often used in damage identification, however the higher modes which are more sensitive to the damage have seldom been researched and utilized. The dynamic information is also influenced by the environment and the measurement noise, so there exist uncertain factors. In this paper the researches on the slab and frame on elastic foundation are studied in this paper, the main works are as follows.1. The researches have been done on modal parameter identification method. Compared with LSCE method, PolyMAX method has better abilities on identifying higher modes and higher damping modes. Modal experiments on free-edged elastic foundation slabs were done by hammer-hitting excitation method in the laboratory. The vibration characters of the slabs on Winkler foundation and on two parameter foundation are discussed, it is indicated that'approximate rigid modes'exist in the slab on real soil condition. The generalized method analyzing the thick-thin slab on Vlasov foundation has been researched, the physical parameters of the foundation are identified by the inverse analysis.2. The modal experiment on a reinforced concrete frame structure on soil foundation was done in laboratory. The displacement mode experiment was done with increasing of the storey, the modal experimental results of four cases were obtained. The strain mode experiment was done and the strain modes were also obtained. Four different factors influencing the uncertainty of modal parameters are considered, including repeated experiments, modal analysis method, varieties of the temperature and the varieties of hitting force magnitude. It is found that the influence of modal parameter identification method can not be neglected. With the increase of the temperature, the modal frequencies are decreased. Modal frequencies of the structures are also decreased with the higher hitting force. HHT method is better on identifying the non-stationary signals than FFT method.3. Physical parameter identification is carried out on the frame structure. The bending shear condensation model is used as the upper structure model, and impedance function model is used as the foundation model. By using the modal parameter identification results in different Cases, the sensitivity method is used to identify the structure's and foundation's parameters in the same time, the regulation of the modal parameter changing with story height is obtained. Due to the ill-posed problems often occurred in sensitivity method, the simulated annealing algorithm is used to combine with genetic algorithm, so GAHA is produced and the global searching ability is developed. GAHA is used in parameter identification, the identified results are better than the results calculated by sensitivity method.4. The concept of modal localization is introduced, the modal localization phenomenon caused by changing support location and support stiffness in continuous beam like structure is discussed by numerical examples, it is due to the expansion of the eigenvalue space in theory. The modal experiments on the fist story beam of a three story height frame structure testify the frame beam has the similar dynamic characters just like continuous beam, the jack's influence on the dynamic characters of frame structure is discussed. By researching on the column of the frame structure, it is found that modal localized phenomenon in continuous beam like structure occurred in frame column, by adding the mass on the column element of first story, the'high sensitive higher mode'is found in experimental results.5. The basic frame work of damage identification based on Bayesian statistical theory is established, Markov Chain's Monte Carlo simulation (MCMC) is used to calculate Bayesian problem. Calculating program of MCMC is compiled. By calculating a three storey shear frame structure, the cases on the single damage location and multiple damage locations, the different criterion and the method under different noise level are compared. It is indicated that Bayesian method based on MCMC method can identify the structural damage effectively. At last, five experiments were conducted before damage and after damage on the frame structure which local column is strengthened, the damage location can exactly be found by using posterior expectation estimation in two step method. It is found that the foundation parameter has obvious influence on structural dynamic characters.