Stress Analysis On Arc Notch Of Orthotropic Steel Box Girder In Suspension Bridge Using Sandwich Deck

With the development of long-span bridges,steel box girders have been widely used,but fatigue cracking has become increasingly prominent.The fatigue cracking at the arc notch of diaphragm is one of the main fatigue diseases of steel box girders.In order to improve the stress concentration of arc notch,a new type of deck structure-steel polyurethane sandwich deck is discussed in this paper.It is made of two layers of steel plate and one core layer of polyurethane elastic.The structure can improve the rigidity of deck,which is lightweight,high-strength and good fatigue resistance.Based on one of the deck segments of a suspension bridge in Dongguan City,Guangdong Province,this paper establishes a segment model of steel box girder made of Steel-polyurethane sandwich deck,and analyses the improvement effect of arc notch stress compared with traditional steel deck,then analyses the form of arc notch and related parameters,finally optimizes the structure by using the results of parameter analysis.At first,this paper introduces the research status of sandwich structure and arc notch.Sectional models of steel bridge deck and Steel-polyurethane sandwich bridge deck steel box girder are established respectively according to actual projects in the second chapter.Overall stress and arc notch stress of the structure under the two schemes are both compared and analyzed.In addition,reasons for the stress characteristics of arc notch are further explored.The third chapter analyses the form of notch in the section model and influence of diaphragm height.Chapter 4 analyses the influence of diaphragm spacing and other parameters on the notch stress in the segmental model;Chapter 5 optimizes and compares the original segmental model with the result of parameter analysis.The results show that compared with the steel deck scheme,the ame quality Steelpolyurethane sandwich deck scheme decreases the stress of deck,longitudinal rib,diaphragm and stress of deck at most.Meanwhile,the stress of notch stress decreases obviously.Further analysis shows that the notch stress of the sandwich deck scheme indirectly affects the notch stress by increasing stiffness and decreasing deformation of the deck.In Steel-polyurethane sandwich deck scheme,original notch form is the best one and the height of diaphragm has little influence on the notch stress.The results of parameter analysis reveal that the parameters such as diaphragm spacing,diaphragm thickness,longitudinal rib spacing,notch clearance and notch radius indirectly affect the notch area through restraint and deformation,so the notch stress change wavily.However,with the increase of thickness of surface steel plate and core layer of sandwich plate,the notch stress decrease.Compared with original segmental model,the quality of optimized Steel-polyurethane sandwich deck decreases by 23% while the stress amplitude of the notch changes little,but the deflection decreases by 47%.Meanwhile,sandwich deck scheme increases the spacing between diaphragms,longitudinal ribs,radius and clearance of arc notches,which reduce the number of welds and help to reduce the fatigue problems.