Deterioration Analysis On Long Spanned Suspension Bridge With Steel Box Girder And Fatigue Reseach For Orthotropic Steel Bridge Decks

The long-span steel box girder suspension bridge,with its unique advantages,has become the first choice for long-span bridges.However,due to the defect of the constraction method,low quality,material defects,corrosion,overloading and inefficient maintenance,there are a variety of diseases in the constructed suspension bridge.Diseases in existing bridges affects not only on normal service of bridges,but also on service safety of structures.In order to ensure the safety of the bridge,it is necessary to carry out scientific inspection,maintenance and technical condition evaluation in time.Firstly,this paper introduces the structural characteristics,development history and operating conditions of large span suspension bridge with steel box girder.And it summarizes domestic and overseas research achievements of various diseases of long-span suspension bridges.Then,for the suspension bridge with steel box girder,the system is divided into six parts:the main cable system,the hungers system,the steel box girder,the anchor,the bridge tower and the ancillary facilities.By collecting and analyzing the domestic and foreign literatures and investigating the diseases in some suspension bridges,this paper summarizes the causes,development trends and influencec on the whole structure.The results show that steel wire corrosion,steel corrosion and fatigue crack of steel box girder are the most common diseases.The corrosion of steel wire and steel parts are mainly caused by the failure of protective measures or anti-corrosion coating damage.Planned detection and and timely maintenance are the key to solve the corrosion problem.The reasons for the fatigue crack of steel box girder are complex,which is often caused by the defects of design and construction,vehicle overload and too much traffic.Afterwards,aiming at the typical disease engineering example of fatigue crack of orthotropic plate,the refined FEM modals are set up to analyze the cause of disease.Constant amplitude fatigue-analysis method and linear damage fatigue-analysis method based on Miner's linear damage accumulating theory and S-N curves are used in this paper.And through the parameter analysis,the method of avoiding the fatigue cracking in the design stage is put forward.The calculation results show that excessive traffic,overload,too thin deck are the main causes of fatigue cracking of U-shaped-rib-to-deck joint near cutout.The fatigue stress amplitude can be effectively reduced by increasing the thickness of the deck.After that,through the comparison of the conservation evaluation standard,Delphi technique are used to put forward the evaluation criteria of the technical condition and the improvement of the disease index value for the long span suspension bridge.At present,the domestic evaluation criterias of maintenance are mainly used in middle and short span bridges or bridges with simple structure.Because of the complex structure load,the criterias are not applicable in the long-span suspension bridges.Delphi technique can be used to modify the disease index of the current criterias by using the experience and wisdom of many experts.Finally,based on the analysis of causes of diseases and diseases index value,this paper sums up the experiences of our predecessors,and summarizes the maintenance strategies of long-span sunspension bridge with steel box girder.Research suggests that the maintenance of the main cable system and hanger system should focus on the jacket and the waterproof device.The maintenance of the steel box girder should focus on anticorrosion coating,treatment and reinforcement of fatigue cracks.The maintenance of anchorage and tower should focus on the repair of concrete defects and the monitoring of displacement and twist angle.