Research In Application Of Time Domain Modal Analysis Methods In Dynamic Nondestructive Testing Of Bridges

In the use of long-term process, the invasion of bridges is not only from earthquakes, storms, natural disasters, environmental corrosion, etc, but also from the improper maintenance, accidents, traffic soared, and other man-made causes of the damage, it is easy to produce all kinds of structural damage, reduce the carrying capacity of the bridge, aggravate the natural aging of bridges and even affect operational safety. Through the dynamic characteristics of the bridge test to detect damage caused by the structural parameters of change, can achieve early detection of diseases, significantly saving the bridge repairs, maintenance costs and avoid the ultimate result of frequent overhaul, must be shut down traffic which caused economic losses, and prevent the collapse of the bridge and other major security incidents.The environment of incentives is used as a source of encouragement in the modal test of bridges. The so-called incentive environment is wind load, vehicle load, such as random shock wave caused by disturbances, stimulated of the amplitude is small, but the frequency response to cover is the rich. In modal parameter identification, there is no need to add special measurement equipment, and also do not interfere the normal operation of the bridge, only using the measured output data available online to identify the structure of modal parameters. Therefore, the use of environmental incentives to identify the modal parameters of bridges is more and more arouse people's attention.Identifying modal parameters is the core of experimental modal analysis. Identifying modal parameters developed a number of mature method, in accordance with the different non-parameter model, modal parameter identification divided into the frequency domain modal parameters to identify and time-domain modal parameter identification. To FRF (transfer function) based on the parameters as frequency domain identification parameter identification; time-domain signal (pulse response function or free vibration) the basis of the parameters to identify as time-domain parameters identification.Based on the study of the various frequency-domain identification method of modal parameters and time-domain identification method of modal parameters, through various means of comparison, the bridge structure environmental incentives for dynamic detection method, this paper selected Random Decrement Technique / Complex Exponential Method for the modal parameter identification methods, and used MATLAB to achieve the procedures. This paper conducted the following aspects:(1) This paper introduced the basic concept of experimental modal analysis and its implementation process, studied the frequency domain modal parameters to identify ways in the least-squares method, rational fraction polynomial method and orthogonal polynomials and Time Domain modal parameters of the recognition method of ITD, Complex Exponential Method, and ARMA model time series analysis methods such as the basic theory.(2) Through various means of comparison, the bridge structure environmental incentives for dynamic testing methods, was selected based on the Random Decrement Technique / Complex Exponential Method for the modal parameters identification method. Through the study of the basic principles of the method, we determined the method for the use of the flow chart of a computer program and calculated using MATLAB language of the establishment of procedures.(3) The theoretical research results of this paper will be used in a Bridge dynamic load test. Get the theoretical frequency and vibration mode of the bridge through the finite element method, then use test data in this paper prepared by the analysis of computer programs to the frequency and vibration mode and conduct a comparative analysis of the results.