Residual Fatigue Life Assessment Of Steel Deck Of Existing Highway Bridge Considering Temperature Effect Of Pavement

Orthotropic steel bridge deck has many advantages,such as light weight,high strength,wide application range and convenience for factory construction,which makes it widely used in various bridge structures.However,with the increasing traffic volume and heavy load ratio and the deterioration of service environment,its fatigue cracking problem is very prominent.At present,there are a large number of bridges using orthotropic steel decks in highway bridges in service,and most of the bridges guard the throat of highway transportation.Once the fatigue cracking of steel bridge decks occurs,the smooth traffic will be seriously affected.Therefore,it is of great significance to accurately evaluate the residual fatigue life of the orthotropic steel bridge decks of in-service highway bridges for ensuring their safety during service,improving their service quality and providing theoretical support for the later maintenance.This thesis takes an in-service highway bridge as the research object,and conducts a systematic study on the welding details of longitudinal rib and top plate in the orthotropic steel bridge decks,which are prone to fatigue cracking and seriously harmful.The main research contents are as follows:(1)The research status and problems of the fatigue life evaluation methods and load spectrum of orthotropic steel bridge deck,the influence of pavement temperature effect on fatigue life,the fatigue life prediction and reliability evaluation at home and abroad are summarized.On this basis,the research ideas and contents of this thesis are clarified.(2)Based on reliability theory and equivalent structural stress method,the residual fatigue life evaluation model of orthotropic steel deck of existing highway bridge is established.The modle can consider the randomness of vehicle loads and materoal parameters,as well as the influence of pavement temperature on fatigue life.Then the calculation methods of relevant parameters in the model are discussed,which provides theoretical support for the practical engineering application of the evaluation model.(3)An integrated model test of pavement and steel bridge deck is carried out to investigate the effects of temperature and pavement on the fatigue performance of the welding details of longitudinal rib and top plate.At the same time,the necessity of considering temperature effect to accurately evaluate the residual fatigue life of orthotropic steel bridge decks is demonstrated.Taking annual damage degree as the measurement index,the effects of annual seasonal temperature and intra-day temperature distribution on the fatigue life of welding details between longitudinal ribs and roof under different roof thickness and three different pavement structures are quantified.(4)Based on the measured traffic flow data of a highway bridge in service,the fatigue load model of random traffic flow is established considering the variation of traffic flow during the service period.According to the established residual fatigue life evaluation model and the research results of pavement temperature effect,the fatigue life of the welding details between longitudinal ribs and roof before strengthening the bridge is evaluated,and the rationality of the established residual fatigue life evaluation model is verified.Then,the residual fatigue life of welding details between longitudinal ribs and roof after reinforcement is evaluated.The research results can provide theoretical basis for the subsequent maintenance of the bridge.