Study On Shear Fatigue Failure Of Rigid And Semi-flexible Composite Steel Deck Pavement

Material selection and structural optimization of pavement layer of long-span steel box girder bridge have important influence on service performance and durability of steel bridge.Due to the influence of heavy traffic and climate temperature,the stress analysis and deformation of bridge pavement are complex,and fatigue cracks,rutting,delamination,overcrowding and pushing diseases often occur in the later stage.At present,the research on bridge deck pavement structure is mostly based on static load,which is not consistent with the actual situation under automobile load,and pavement fatigue research usually relies on time-consuming and laborious experimental means.Therefore,it is an important subject to put forward new ways and methods for analyzing and studying fatigue damage of steel deck pavement structure to improve the service performance and durability of long-span steel box girder bridges.Firstly,by studying the mechanical analysis of steel deck pavement system at home and abroad and the general situation of pavement material and structure design,this paper summarizes some common pavement damage types of famous steel box girder bridges.According to the principle of material gradient design and based on the standard section of steel box girder bridge,a three-dimensional finite element model of rigid and semi-flexible composite steel deck pavement structure is established by using ANSYS finite element software,which includes orthotropic steel deck,diaphragm,U-rib,bottom high toughness lightweight concrete,middle cement mortar coagulation and upper SMA steel deck composite pavement structure.On this basis,the influence of steel deck structure and pavement thickness on the mechanical characteristics of composite pavement structure is analyzed.The shear stress variation law and the influence factors of shear strength of steel deck pavement system under various loading data are obtained by finite element mechanical calculation.Finally,the fatigue reliability of rigid and semi-flexible composite steel deck pavement is analyzed by using nCode Design-Life fatigue analysis software.Based on the actual working condition of the steel bridge,the fatigue type of the whole steel bridge section is determined,and the S-N fatigue design curve of the composite pavement structure is calculated.Considering the practical application,the pulse cyclic load time and displacement period are input to analyze the fatigue damage of the composite pavement structure.The results show that the lower the speed of load,the greater the interlaminar shear stress of the steel deck pavement structure;when the load travels to the position above the junction of diaphragm and U rib,the shear stress of each layer,interlayer and the whole structure is the largest;the shear stress of each layer is less than 1 MPa,the interlaminar shear stress is 2.83 MPa,and the shear stress of the whole structure reaches 8.96 MPa,and the shear stress of the pavement and the steel bridge deck reaches 8.96 MPa.The interlaminar shear stress is the key factor affecting the overall shear strength;the position of composite steel deck pavement structure prone to fatigue damage is the same as the maximum shear stress at the junction of U-rib and diaphragm.so steel plate is more likely to fatigue than pavement;the life of the whole local steel bridge section is more than 106 cycles,which meets the safety requirements;and the fatigue life of the weakest part is 1.065 x 106 cycles.The joint of U-rib,steel bridge deck and diaphragm is the main cause of fatigue damage of pavement.Improving the stiffness and strength of these places is helpful to further optimize the pavement structure of steel bridge deck.