Theoretical Study On Strengthening Diaphragm Cutout On Steel Bridge Decks With High Elastic Modulus Carbon Fibre Reinforced Polymers

With light weight,large intensity,high degree of factory orthotropic steel bridge(OSD)structure are widely used in bridge construction.However,its welding seam is dense,stress concentration,easy to appear internal defects.In particular,the fatigue cracking problem of diaphragm cutout is quite serious,which has attracted the attention of bridge researchers.In this thesis,the diaphragm cutout is taken as the research object,and the fatigue performance and reinforcement performance of high elastic modulus CFRP plate are studied in detail.The main work is as follows:(1)By loading the impact surface of a steel bridge segment model,the stress characteristics at the diaphragm cutout on steel bridge decks are obtained.The results show that: under the action of wheel load,compressive stress is always applied here,and the high level tensile stress after welding is considered to be the main factor causing fatigue cracking at this position.(2)The welding process of longitudinal and transverse ribs of orthotropic steel bridge deck was numerically simulated by thermomechanical sequential coupling method.Based on the verification of the correct welding temperature distribution,the welding stress field was solved and the stress distribution at the diaphragm cutout was obtained.The results show that the peak value of residual stress at the diaphragm cutout reaches 220 MPa,which changes the stress cycle characteristics and causes the crack to appear and further expand.(3)When the wheel load stress and welding residual stress are superimposed,the diaphragm cutout’s position stress characteristics is transformed from compressive-compressive stress cycle to tension-tension stress cycles or tension-compressive stress cycle.The finite element model of fatigue analysis was established by extended finite element method,the fatigue property of diaphragm cutout was evaluated.The results show that the cracks here are type I cracks,and the fatigue life of the cracks here is about 5.7642 million times under single wheel loading under the most unfavorable load conditions.(4)The high elastic modulus CFRP reinforced diaphragm cutout on steel bridge decks was established.Through the change of stress intensity factor amplitude,the parameters of CFRP plate length,width,thickness,elastic modulus and shear modulus of adhesive layer were systematically analyzed.The results show that the stress intensity factor at the crack front is most sensitive to the change of the width of CFRP plate,followed by the change of the shear modulus of adhesive layer.The length,thickness and elastic modulus of CFRP plate have a certain influence on the strengthening effect of CFRP plate.(5)Considering the relationship between reinforcement effect and reinforcement cost,different parameter combinations were selected to calculate and recommended reinforcement parameters were given to evaluate the fatigue performance of the diaphragm cutout after reinforcement.The results show that the initial fatigue crack will not propagate and the fatigue life can be significantly improved when the recommended design parameters are used to reinforce the diaphragm cutout.There are 79 pictures,8 tables and 101 references.