Rapid Assessment Of Bridge Safety Through Impact Testing

Bridge is the hub of traffic engineering, which is related to the social and economic development. But bridge inevitably occurred in various of structural damage during the long process of application. The major causes of injury are corrosion, extreme natural disasters such as earthquake, typhoon and improper use, maintenance and other human factors, which contribute to the attenuation of bridge structural resistance and safety hazards. Bridge detection and structure health monitoring technology are the main methods for maintenance and safety evaluation of bridge. However, the regular detection methods are mainly based on artificial which is laborious and time-consuming, while structural health monitoring system is expensive and complex which also can not be widely used to maintenance of small and medium bridges in extremely limited safety assessment. Therefore developing fast, convenient and reliable bridge rapid testing technology is an important means to realize the safety evaluation of small and medium bridge on the national highway network. This paper mainly studies on bridge rapid safety assessment method based on the impact vibration test, and research and innovation are as follows:(1) Bridge rapid test and evaluation system are put forward. Firstly, the theory that the structure information derived from impact vibration data and environmental vibration data is different has been verified. Namely the frequency response function (FRF) calculated from the shock vibration measurement data is real whose amplitude is same as the theoretical value, while the frequency response function (FRF) estimated from the environmental vibration test is scaled, thus using impact vibration test for structural identification has a fundamental advantage. Secondly the development of hardware for the bridge fast test is introduced, mainly including the new impact loading device and automatic sensor installation device. Impact loading device produced the impact caused by the free fall of the heavy hammer, and it can provide large amplitude, broadband domain and high quality impact vibration data. Automatic sensor installation device can realize automatic installation and disassembly of the sensor in the course of the vehicle, a significant reduction in test time, significantly reducing testing time, both of them service quick test and evaluation on the bridge. Finally, the framework of the bridge rapid test system based on impact vibration test is established. The bridge rapid test system is convenient and based on the deep theory of deep structure parameters identification, and it can reliably realize the structure identification and bearing capacity evaluation of the bridge.(2) The displacement flexibility identification theory based on impact vibration test is study on. Structure flexibility matrix as the inverse of the stiffness matrix is an important parameter which is closely linked to the structural damage identification and structural load carrying capacity evaluation. This paper summarizes the calculation methods of displacement frequency response function from two aspects, Including the definition, modal formulas and complex modal formulas, frequency response function estimation of multiple input multiple output. It is found that the modal scaling factor is the key to identify the structural flexibility in the derivation of the formula. A variety of methods to calculate the displacement flexibility from impact vibration test is deduced, including the calculation of the displacement flexibility under the conditions of known mass and how to use the CMIF method to identify the frequency, damping ratio, modes, displacement flexibility under the conditions of unknown mass. Using CMIF method to identify the structural displacement flexibility does not need to know the quality of the structure, so it has extensive practical value.(3) Bridge block impact vibration test with multi-reference points has been proposed and research on. The traditional impact vibration test method is for the whole structure, and there are many problems in test cost and efficiency. In this paper, structure block impact vibration measurement is proposed, only observing the response of the nodes in substructure, so it has the advantage of reducing the number of sensors and realizing the rapid impact vibration testing of a bridge, but the problem is how to fuse the substructure data to get the full structural features. In order to solve this problem, this chapter proposes the multi-reference point method to fuse the data of each sub-structure. When divideding the whole structure in the multi-reference point method, the adjacent sub structures have the same node in the boundary. The fusion of the sub-structure parameters can be realized based on displacement mode continuous at the boundary of adjacent sub-structure. Finally we can get the displacement flexibility matrix of the whole structure, and the effectiveness of the proposed method is verified at last.(4) Bridge block impact vibration test with only a reference node has been proposed and research on. A much more efficient and applicable method has been proposed based on the research of the multi-reference points method. When divideding the whole structure in the single reference point method, the sub-structure have only one commom node and the selection of the reference point is arbitrary. The fusion of the sub-structure parameters can be realized based on the phase angle curve of reference point. Finally we can get the displacement flexibility matrix of the whole structure, and the effectiveness of the proposed method is verified both by experiment and numerical simulation at last.