| With the vigorous rise of the urban rail transit industry and continuous changes under the background of the new era,the development of urban rail transit steel structure bridges is also changing with each passing day.Based on the background of rail transit,the fatigue problem of orthotropic steel bridge deck has gradually become one of the hot research topics in the field of bridge engineering,and it is also a fundamental problem that restricts the further development of rail transit steel structure bridges.The paper is based on the Chongqing Construction Science and Technology Project "Research on the Lateral Rigidity and Fatigue Design of Steel Box Girder of Large-Span Urban Rail Transit Bridges",summarize and sort out relevant domestic and foreign research and specifications,refer to the structural type and size of the orthotropic steel deck of the real bridge,start with its fatigue load,force characteristics,fatigue resistance design method,fatigue details and hot spot stress analysis,and pass the full-scale model fatigue test and finite element theoretical analysis are combined to evaluate and optimizate the fatigue performance of orthotropic steel bridge deck.The main research conclusions are as follows:(1)For the rail transit standard fatigue car,the axle load is the design axle load of the train multiplied by the reduction factor 0.8,and the wheelbase is the design wheelbase of the train;The number of trains in the standard fatigue car and the fatigue loading conditions are closely related to the operation and management planning within the design life and the length of influence line of analysis part.(2)Use ANSYS software to realize mobile loading and perform hot spot stress analysis on the fatigue details that are of great concern.Each hot spot stress-time history curve focused on fatigue details obtained under the action of single-line adjacent four-axis fatigue load has symmetry and the validity of adjacent loads;the stress time history curve produces a total of 2 stress cycles,which can be regarded as the "repetition" of the time history curve under two single-line biaxial loads,and the maximum stress value of the fatigue details at the connecting position of the bridge deck and the U-rib is about 1.4 times that under a single-line uniaxial load,the fatigue details at the opening arc of the diaphragm is about 1.6 times,the fatigue details of the connecting position of the U-rib and the starting point of the diaphragm opening is about 1.7 times.(3)Carry out the full-scale model fatigue test.Within 2 million cycles of fatigue loading,the stress-load curve of the key measuring points on each component shows a linear relationship,with good symmetry and recoverability,and there is no obvious sudden change,the stress value only fluctuates within an acceptable range;after 1million fatigue cycles are loaded after increasing the load amplitude,the stress value of the measuring point still has no stress mutation phenomenon and no fatigue cracks;that is to say,the fatigue details studied are under the conditions of higher stress amplitude and long service period,it still has good fatigue performance and high safety reserve.(4)Evaluate the fatigue details based on the S-N curve in the AASHTO specification;the fatigue check design stress amplitude and the predicted total fatigue life meet the design requirements of 100 years of service life.The fatigue stress amplitude of the optimized orthotropic steel bridge deck is reduced by up to 56.1%co MPared with that before optimization.It is also pointed out that the opening arc of the diaphragm and the connection position of the bridge deck and the U rib are the sensitive areas that are most likely to cause fatigue failure in the future and require later bridge maintenance and inspection. |
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