| Orthotropic steel bridge deck is a complex spatial structure formed by welding of longitudinal rib,diaphragm and bridge deck.It has the advantages of large bearing capacity,low component weight,short prefabricated cycle,and superior structural safety,applicability and economic performance.In recent years,a large number of penetrating cracks have been detected on steel bridge panels,which seriously affect the service performance of Bridges and have hidden dangers for driving safety.Usually,fatigue cracks through the roof will destroy the bridge deck pavement,which causes the attention of inspection personnel.At this time,the repair cost is high and the repair effect is poor.The existing researches on fatigue cracks of orthotropic steel bridge deck mainly focus on the propagation behavior and fatigue life of non-penetrating fatigue cracks,but few scholars have studied the propagation behavior of cracks completely penetrating the roof and its influence on the overall performance of bridge deck.In view of the existing detection results show that there are a lot of penetrating cracks in the steel bridge panel,the propagation behavior of fatigue cracks after penetrating the roof is worth further study.Supported by the National Natural Science Foundation of China(51908068)project"Fatigue Reliability of Steel bridge deck Roof Seam considering Multi-crack Coupling Propagation",this paper selected the longitudinal rib and roof seam of steel bridge deck as the research object,and adopted the finite element method to study the propagation behavior of penetration fatigue crack.The numerical simulation results were verified by through-fatigue crack propagation test of full-scale steel bridge panel model.The main research contents are as follows:(1)The analysis theory and calculation method of fatigue crack on steel bridge panel are summarized,which provides theoretical methods and processing tools for subsequent research.Based on the basic theory of linear elasticity,the crack cracking modes and crack cracking types are introduced,and the current mainstream effective numerical methods for calculating complex cracks are described.The internal relationship between stress intensity factor K and crack growth rate Da/dN in fatigue crack growth model was elucidated according to fracture mechanics theory,which provided theoretical basis for the analysis of crack path and dominant crack type.(2)Based on the engineering background of Nanxi Yangtze River Bridge,finite element analysis of orthotropic steel bridge deck was carried out.The whole bridge segment model and the segment model of crack propagation area were established by using ABAQUS software for stress analysis.According to Dload impact surface,the most adverse loading condition at welding detail’s was determined to be flexural outside the plate.Combining FRANC 3D software,the simulation of roof weld root(80%penetration rate)outside the plate bending conditions throughout the fatigue crack extension process,get through the initial stress intensity factor of fatigue crack in the type and size control parameter a,there is a proportional relationship,compound cracking test results conform to the engineering practice,to simulate the mode I crack can be used as the most unfavorable situation.It provides theoretical support for mechanical properties and stiffness degradation under the most adverse extension.(3)Based on fracture mechanics theory,the numerical simulation method and steps of fatigue crack propagation at weld root of bridge deck were given.Parameter analysis was conducted for collinear double-penetration fatigue crack at weld seam of bridge deck-U rib under the most adverse stress condition(bending outside the plate)by using ABAQUS-Franc 3D interaction.It is concluded that the initial stress intensity factor level of the collinear double-through-crack is higher than that of the single-through-crack.Within s/A≤0.75,the crack spacing increases to 0.75<S/a and there is no significant coupling effect.The larger the auxiliary crack size is,the more obvious the coupling effect is.The growth rate of the double crack is faster than that of the single crack,and the influence range is limited by the coupling effect,and the crack size is linearly related to the influence range.(4)for the full-scale orthotropic steel bridge panel type single through fatigue crack extension fatigue test,the specimen surface loading area set up in line with the equivalent area of the rubber bearing of wheel load,by moving head and bearing simulation after shop is passed a single wheel uniformly distributed load,the design into action under fatigue load of strain measurement,static load strain measurement,Hot spot stress method was used to calculate the stress at the bridge panel-U rib weld,and the change of crack tip propagation of prefabricated fatigue crack was recorded.The static stress values of each measured point before fatigue loading of components are consistent with the theoretical values calculated by finite element method.The measured longitudinal propagation and deflection distance are slightly smaller than FRANC 3D simulation results,and there is an acceptable degree of error,which verifies the effectiveness of THE simulation results of ABAQUS-Franc 3D crack growth. |
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