| The development trend of the modern bridge is the large-span. The span has been developed form 1050 meters of Golden Gate Bridge Completion in 1937 to 1991 meters of Japanese Shi Bridge completion in the 90's. In our country, to enter since the 80's, the development of long-span bridges was rapid. The spans of Suspension bridges, cable-stayed bridge, continuous rigid frame bridge, arch-shaped bridge have entered the ranks of the world's most advanced. Modern large-scale structure of the bridge is characterized by large, light, flexible, and more sensitive to the role of the wind, the wind load has become the dominant load. Therefore, the introduction of the wind analysis of the bridge has become a large-scale bridge design in an important task.In addition, the seismic loading is also a large-scale bridge design must be considered an important factor. With the construction of science and technology and the rapid advances in earthquake engineering theory and practice has been greatly developed in comparison to the establishment of the works reflect the actual seismic design method. In these methods, it can not be separated from the structure of the dynamic characteristics accurately.Through the establishment of a purely theoretical dynamic model of the structure to obtain the dynamic characteristics of the structure has been unable to meet the structure of the wind, seismic requirements, the need for correction through the measured to theoretical models, thus improving the structure of the dynamic model. Through the test mode to identify the inherent structure of the bridge mode is by far the most reliable method.Rigid Frame - continuous girder bridge is to draw T-Frame and continuous beam structure of the merits of the two developed a bridge structure, are more suitable for long span bridges of the General Assembly. Its rigid-frame pier can be double-thin-walled flexible to reduce the thermal stress, shrinkage and creep of concrete piers of the impact of continuous beam pier slip through the release of the level of support the level of force. Rigid Frame-continuous beam structure of reasonable force to prevent a large-tonnage also support the use of the highway on the bridge deck to achieve a smooth and comfortable traffic requirements.Semi-rigid frame - continuous girder bridge inherited rigid frame - the advantages of continuous girder bridge in China has been widely used. Bridge structure of measured parameters of improper motivation may reflect the construction quality of bridges for the state, but also that the seismic design of bridge structures to provide strong theoretical support. Therefore, to carry out semi-rigid frame - large box-girder bridge for the power detection technology to create dynamic parameter identification method is very necessary.Dynamic parameters of the structure of traditional identification methods to be measured at the same time the measuring point excitation and the dynamic time-history response curve, based on the frequency domain the frequency response function (FRF) or the time-domain impulse response function (IRF), the driving force of structural parameters identification. Dynamic parameters of the structure of traditional identification methods to identify the main Klosterman iterative method, Levy law, Fitting orthogonal polynomials, and optimize the identification of law, time-domain complex exponential fitting, Ibrahim time domain method, ERA methods. Dynamic test as a result of the bridge, it is very exciting force can not be collected from the time-response measurements require only the use of dynamic response to time-points to identify the dynamic parameters of the bridge, so the traditional identification methods can not identify the dynamic parameters of bridges.Collected from the measuring point of the bridge dynamic response can be divided into freedom of the general decay and the environment, inspired by two broad categories of random response. People in the traditional method based on the identification, carried out in response to signals from the two categories to identify dynamic parameters of bridges. The current from the random responses can be used in the bridge method to identify dynamic parameters of the main peak method, frequency-domain decomposition method, sequence analysis, a random sub-space law.The use of random decrement technique, a random response from the measured points can be drawn in the free decay response, the attenuation from free access to the structure of how to respond to the dynamic parameters caused by the attention. Feeny and Kappaggantu the first time discussed the response from the free vibration of structural dynamic parameters of extraction methods, the use of orthogonal eigen-decomposition method to get the structure of the vibration mode, if the quality of the unknown matrix structure, the identification can not be so its application is limited. Kerschen and Arunasis then others from the free vibration response of structural dynamic parameters extraction methods for further research, this method is more complicated process, suitable for small damping system. 2008, Wang Bor-Tsuen and Cheng Deng-Kai, a more convenient, just based on the displacement of free vibration modal response analysis. On the premise that the structure of the damping coefficient needs known, and this parameter in the dynamic testing of bridges is not known, it will limit the application of this approach.The impact of vehicles on the bridge of the complexity of the impact of the role of factors, but the role of the impact can not be made fully consistent with the theoretical analysis and practical terms, in the theory of probability-based analysis methods and parameters for many of the statistics is not resolved before the work had to With the experimental method, through the experience of the "shock factor" to be similar to the formula to reflect. There are many countries in the world and the old bridge in need of repair and assessment of its carrying capacity, the need for a more accurate and convenient method of calculating the impact factor. Therefore, the impact coefficient of the bridge is still in many countries and regions, such as the United States, Canada, Japan, Australia and so on.In this paper, the use of random decrement technique inspired from the environment to extract the random response of the free decay response; the use of modern methods of wavelet transform to form from the free decay response of bridge structures to identify the frequency and mode shape of the theoretical methods; frequency identification based on the results of the free decay response through the band-pass filter, and filtering is derived from the free decay signal after the analysis of the structure of the bridge damping ratio of the order of the theoretical methods.The purpose of the test in clear and based on the premise of the pilot, the establishment of the finite element model, the independent optimization of the use of effective inter-large-half of a 7 - rigid frame box girder bridge for the power structure of the measuring point, the use of optimization results and the actual method of combining determine the dynamic determination; this environmental incentives Bridge, a bridge collection, inspired by the structure of the environment of the dynamic response of the measuring point. Random decrement technique to extract from the random responses of the measuring point of the power of the free decay response, from the free decay response, respectively, to identify the structure of the bridge frequency, vibration mode and damping ratio.Coefficient on the impact of influencing factors and the impact of domestic and international norms on the provisions of coefficients and the method of calculating an in-depth analysis. Inspired by sports car on a bridge test the impact factor calculation. In the above-mentioned theory, under the guidance of a large cross-seven semi - rigid frame box girder bridge to carry out sports car for testing, the use of collected displacement response, analysis of the impact factor of this bridge.
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