Fatigue Performance Of Orthotropic Bridge Decks Based On Traction Structural Stress Method

Orthotropic bridge decks possess some advantages over other steel bridges,including lightweight,significant structural stiffeness,convenient assembly,and perfect comprehensive performance.The lightweight performance translate a steel savings by 50% than traditional steel bridges.Fatigue cracks are observed in bridge roofs,U ribs,and crossbeams in orthotropic bridge decks in service under vehicle wheel loadings,which shortens the service life of bridge decks in service.The simplified uniaxial S-N curve predition method mainly considering normal stress is applied in fatigue design standard and existing researches in bridge field.However,the specific positions in orthotropic bridge decks such as arc-shaped non-welded zone is in a state of complex stress.The existing standard can not be directly applied,and the accurate bridge design life can be directly affected by the application shortages.Besides,various failure modes are not uniformly predicted in existing predictiong methods.At present,a large number of cross-sea bridges are built in China,fatigue performance researches of bridge components are carried out based on a large amount of talents and material for the design and construction of each orthotropic bridge decks.However,the fatigue failure mechanism is still not clarified with engineering data redundancy,and it has been rised as the theoretical guiding principal in the bridge field.Therefore,it is essential to propose the universal method for accurately predicting the bearing state,failure mode and fatigue life of orthotropic bridge decks in the bridge field.The systematic research on the fatigue performance of bridge roofs,U ribs,and crossbeams is carried out in this paper based on the existing problems.Three aspects of contents are as follows:(1)Experimental study and analysis on fatigue performance of bridge roofsFatigue tests with fatigue crack throughout the bridge roof under tension-tension fatigue load were designed with 36 orthotropic bridge roof specimens.The rationality analysis of specimen size is discussed based on the measurement results of residual stress of various width specimens.The fatigue failure path with cracks throughout the bridge roof of bridge roof specimens is defined based on the phased array monitoring results,and the failure path based on fatigue test is compared with the failure path with crack throughout the bridge roof using the traction structural stress method.The effect of weld quality parameters,such as the single-sided and double-sided weld types,penetration rate,angular deformation and stress ratio of fatigue load,on fatigue performance of orthotropic bridge decks are researched.The calculation formula of equivalent structural stress is raised with the consideration of the parameter effect on fatigue property prediction.The theoretical system of equivalent structural stress method can be improved.(2)Experimental study and analysis on fatigue performance of U ribsThree-point bending fatigue tests with crack initiating at U rib weld toe were carried out on 6 U rib specimens by setting reasonable constraint distance.The applicability of the traction structural stress method for predicting the failure mode of U rib is discussed.Various failure modes in three-point bending fatigue tests in bridge field are predicted,and the relationship between failure mode and constraint distance of bridge decks in three-point bending tests is proposed,which provides the design basis for three-point bending tests of orthotropic bridge decks.The master SN curve based on the traction structural stress method for predicting the fatigue property of welded joints in orthotropic bridge decks is established based on the fatigue test and evaluation results by traction structural stress method.The fracture mechanism of cracks in the U rib weld toe is solved and clarified and the fatigue desin criterion of bridge decks is improved.(3)Fatigue performance of bridge decks considering the complex stress stateThe combined traction structural stress method considering effect of shear stress is applied to evaluate the fatigue performance of non-welded zone,and the fatigue crack initiation mechanism of the arc-shaped non-welded zone of crossbeams in orthotropic bridge decks is clarified.The complex stress state of arc-shaped nonwelded zone is accurately described,and the applicability and accuracy of the method are verified.The parameter analysis is carried out to clarify the influence of loading mode,weld seams and structural parameters on the fatigue property of bridge decks,using the combined traction structural stress method verified by fatigue test,which provides guidance for the maintenance,reinforcement and fatigue design of bridge decks.