Research On The Fatigue Life Of The Steel Bridge Deck Pavement Based On The Fracture Mechanics

As a critical technology to the long span bridge construction, paving the steel bridge deck has become a research hotspot abroad and domestically in recent years. Based on the summarization of current research on the steel bridge deck surfacing, the limitation of the current designing method of the deck-paving was pointed out. Based on the fact that the deck-pavement works with cracks during its work-life, the fracture-mechanics theory can be applied to study the fatigue-life of the steel bridge deck pavement.In this thesis, the surface crack of the orthotropic steel bridge deck pavement was the research object. The variation and the effect parameters of the SIF (stress intensity factor) at the crack and the calculating parameters of the Paris's model was the central researching content. combined with several research projects of the deck-paving, the following tasks was accomplished in this thesis:1 The finite element model of the steel deck system with a three-dimensional crack was created and the SIF of the crack was calculatedThe three-dimensional finite element model of the orthotropic steel bridge deck system with a surface-crack was established; the 12-noded three-dimensional singular element, the r-1/2 singularity of which was testified, was constructed. The 12-noded three-dimensional singular element being laid along the crack front to model the singular stress and strain field, the SIF was calculated. The general command flow and computer code was compiled to finish the modeling and calculation based on the secondary developing function of the general finite element software.2 The SIF of the surface crack of the orthotropic steel bridge deck pavement was analyzedThe maximum tensional strains of the pavement surface with or without a crack on the pavement were calculated and compared. It was found that the crack on the pavement can reduce the maximum tensional strain, which showed that the controlling index of the cracked pavement is not the maximum tensional strain, but the singular stress field intensity at the crack front. The surface crack of the pavement is the composite crack, the equivalent SIF reflects the composite effect of three basic cracking models; In this thesis, three basic SIF and the equivalent SIF were calculated and analyzed.The SIF changed along the crack front. Thus, the maximum SIF along the crack front was found and was regarded as the representation of SIFs along the crack front. The SIF varying with the loading position of the axle load was analyzed and the worst loading position of the vehicle axle load was determined.Lots of the structural parameters of the orthotropic steel bridge deck system affect the mechanical condition, thus affect the fatigue cracking of the pavement crack, which can be exhibited by the SIF varying with the parameters. Through amount of numerical calculation, the effect of all the structural parameters on the SIF was analyzed.The expanding state of the pavement crack changes with the cracking depth, which can be showed by that the SIF is the function of the crack depth. By amount of numerical calculation and data fitting, the SIF was expressed as the quadratic polynomial of the crack depth. The coefficient of the quadratic polynomial changes with the structural parameters of the deck system. To forecast the quadratic polynomial of any deck system, a BP neural network model was created.According to the expression of the SIF to the crack depth, the critical expanding depth of the pavement surface crack was determined.3 The multi-layered heat exchange partial differential equation group of the steel girder with pavement was built and solved. The effect of the varying temperature on the expand of the pavement surface crack was analyzedThe varying temperature can cause thermal stress in the pavement, and the crack SIF changes with the thermal stress, which indicates the effect of the varying temperature on the expanding of the crack. In this thesis, the multi-layered heat change partial differential equation group of the steel box girder with pavement...