Research On Structural Durability And Health Monitoring Of 70m Box Grider Beam Of Hangzhou Bay Bridge

Durability and structural health evaluation are two important factors influencing the safety of the bay bridge. Hence the research focuses on the durability and health evaluation of the 70m box girder of the Hangzhou Bay Bridge. Considering the structural and environment characteristics of the Bridge, the study analyzes main influencing factors of the structural service life and the failure probability laws by using the concrete theory, the mechanics, the systematic theory, the testing technique, the signal processing, the information network, the durability theory, the dependability theory, the dynamic damage identification system, the artificial neural network and the probability statistical analysis. The study also designs the health monitoring system and discusses signal processing techniques and damage diagnosing methods. Further, the theory foundation and the processing technique of HHT signal processing method are put forward and the artificial neural network of the 70m box girder structural dynamic damage diagnosing system is founded. All these will provide theoretical foundations, measuring methods and signal processing methods for the service management of the Bridge.By all the studies, the following conclusions are drawn.Firstly, by studying on the thickness of concrete cover, the Cl~- initial density, the Cl~- diffusion coefficient, the Cl~- critical density, the Cl~- density on the structural surface and their probability distribution characters, the statistical distribution characteristics and probability density function are derived. Besides, the law of the durability failure probability of the 70m box girder is presented and then the random dynamic probability is forecasted which can be used as theoretical method of the durability evaluation of the 70m box girder.Secondly, the signal collection and transmission technique which is suitable for the health monitoring of the large span bay bridge are brought forward. At the same time, the general survey, sensor sub-system, signal collection and transmission, signal processing sub-system, design principle and application method of the structural health comprehensive sub-system are expatiated.Thirdly, HHT is used to analyze the nonlinear and non-stationary signals for diagnosing the faults in bridge structure. How to extend the boundaries of the analyzed signal for sifting process is a key problem of HHT. And a new technique based on response surface method is presented to deal with the difficult problem. It has been proved that the existing methods, that is AR model method and linear neutral net method, are special cases of the new generalized method. The boundary extension problem arising from HHT can be described by mathematical programming, and traditional gradient algorithms may diverge when the Hessian matrix of the object function is non-positive. It has been proved that the solution of the original programming problem can be obtained by solving linear equations which is solved by SVD. HHT is used to diagnose the damage of the practical bridge, and analysis results show that the method with new boundary extension technique performs successfully.At last, the dynamic damage diagnosing system of the 70m box girder is founded on the basis of the artificial neural network by considering the structural design and construction characteristics of the 70m box girder. This system can identify the position and extent of the local damage effectively and consequently complement the structural health monitoring system of the 70m box girder. Besides, it can guarantee the Hangzhou Bay Bridge's safety during service and thereby has significant theoretical and practical meaning.