Research On Fatigue Damage Of Orthotropic Stell Decks Using Externally Bonded Carbon Fibre Reinforced Polymers

In recent years,with the rapid growth of traffic volume and overloading factors,the disease of fatigue cracking of orthotropic steel bridge which is widely existed and has not been effectively solved has become more and more serious.Along the technical route of this paper “discovery fatigue disease,research fatigue disease,repair fatigue disease”,through investigation of fatigue damage,analysis of the causes of fatigue,fatigue strength calculation,fatigue life evaluation and reinforcement of fatigue,the fatigue problems and the solutions to fatigue problems are discussed.Find fatigue disease.Investigate the typical fatigue cracks of orthotropic steel decks.Starting from the details of structure,analysis the stress characteristics of the structure.The causes of the disease are divided into the main causes of structural details and external loads,and the causes of cracks in fatigue are discussed comprehensively from the angles of out of plane deformation and stress amplitude.Finally,the causes of cracks in longitudinal rib butt joint,bridge plate and longitudinal rib fillet weld,and transverse and longitudinal rib fillet welds are analyzed emphatically.Research fatigue disease.The similarities and differences of American AASHTO,European Eurocode,Japan bridge type book and Chinese code for design of highway steel structure bridge were analyzed around the fatigue safety criteria,the fatigue strength grade division and the standard fatigue model.According to codes of various countries,checked the typical fatigue details of orthotropic steel bridge deck.Besides,a finite element model with cracks is established by means of the large commercial finite element software ANSYS with the aid of sub model technique.Meanwhile,on the basis of linear elastic fracture mechanics,the stress intensity factor of crack tip under different crack lengths is calculated by displacement extrapolation method,and the concept of effective stress intensity factor is introduced to consider the composite of stress intensity factor.And then,the fatigue crack propagation life is evaluated based on the Paris formula.Finally,the fatigue crack growth regularity of different fatigue vulnerable details and thr factors of fatigue life are discussed.Repair fatigue disease.Simulate CFRP which is introducd into the fatigue life assessment model with cracks by coupling nodes degree of freedom,with shell41 elements with no external stiffness,the fatigue strengthening model is established.It makes the calculation of stress intensity factor at the crack tip under CFRP reinforcement come true.And then,the stress intensity factors were treated by dimensionless method,and the parameters of CFRP fiber laying direction,elastic modulus,width,thickness and length were analyzed under the variation of dimensionless stress intensity factor.The results show that the increase of CFRP size(length,width)and stiffness(thickness and elastic modulus)can both reduce the stress intensity factor at the crack tip.Based on the principle of reasonable utilization of CFRP material and considering the relationship between reinforcement cost and reinforcement effect,a set of optimum reinforcement parameters for U rib butt welding joint is obtained.Under the combination of the optimum reinforcement parameters,the fatigue life of the butt welded joint with U ribs is evaluated.The results show that CFRP can significantly increase the fatigue crack propagation life.