Research On Fatigue Property And Fatigue Crack Repair Methods Of Orthotropic Steel Bridge Deck

The orthotropic steel bridge deck has been widely used in the bridge structures because of its advantages of high carrying capacity,light weight and easy to be constructed,which can effectively solve the contradiction between bridge structure's weight,bearing capacity and span.With the development of economy and the increase of traffic flow,both frequency and intensity of the vehicle load imposed on bridges begin to increase,resulting in frequent occurrence of cracking in the orthotropic steel bridge deck in service bridges,thus reducing the load carrying capacity and service life of the bridge deck,which has become the typical problem for large span bridge.U rib-deck weld crack is one of fatigue cracks that often occur in the orthotropic steel bridge deck.Previous studies on this type of fatigue crack mainly focused on single small dimension specimen.In practice,the stress of the bridge deck is redistributed after fatigue cracking,so the fatigue performance of the U rib-deck welded joints in the actual structures cannot be fully reflected by the investigation on the single small dimension specimen.In addition,for the fatigue cracks in the bridge decks which need to be repaired,the existing repair methods are too onefold,and there is a lack of relevant research on the combination of multiple repair methods.Therefore,it is of great significance to study the fatigue property and fatigue crack repair methods of orthotropic steel bridge deck.In this paper,based on "the characteristics of the property evolution of extra-large span bridges under multi-factor action"(2015CB057703)which is a sub-topic of the national basic project(973project)"the basic theory research on the design and evaluation for the safety of extra-large span bridges",the experimental research on the fatigue property and fatigue crack repair methods of the multi-size(length)orthotropic steel bridge decks are carried out.Details of this study are summarized as follows:(1)According to an actual bridge,5 groups of 32 specimens of orthotropic steel bridge deck with different lengths were designed and manufactured.Through the finite element analysis,the stress distribution was computed and the position of the strain gauges was accordingly determined,based on which the fatigue test scheme was formulated.(2)Fatigue tests on specimens were carried out,and fatigue crack propagation,stiffness degradation,fatigue life and fracture morphology were studied.The results show that the initiation and propagation of cracks can be divided into 4 stages: crack initiation,crack macroscopic expansion,crack penetration plate thickness,fatigue fracture.The stiffness degradation rate of the specimens increases with the increase of the cycles number.When thestiffness degradation rate reaches about 0.1,the remaining fatigue life of one specimen is about 20%.Comparing the fatigue test results with the standard S-N curves,it is proved that the formula of anti fatigue design is conservative.The L-S-N curve is established according to the length of the specimens.The fatigue cross section of all specimens are flat,which can be mainly divided into fatigue source zone,fatigue crack stable expansion zone and instantaneous fracture zone.The smaller the stress amplitude is,the more the number of cycles and the smaller the instantaneous area.(3)The advantages and disadvantages of the existing repair methods are analyzed,3suitable repair methods are selected from which,and 6 repair schemes are made to repair all the cracked specimens.According to the fatigue test scheme,the fatigue test scheme for the repaired specimens is formulated.(4)Test the repaired specimens,and analyze their failure modes,stiffness degradation and fatigue life.The results show that the repaied specimens were more prone to multiple cracks,and the time from which the main cracks appear to the specimens failure is shorter than before.At prophase of fatigue loading,the stiffness degradation rate of the repaired specimens is higher than intact specimens.After the stiffness degradation rate reaches 0.1,the degradation rate of intact specimens begins to accelerate obviously,and the final stiffness degradation rate of most repaired specimens is lower than that of intact specimens.In the 6repair schemes,the combination of the upper and under reinforcement steel plate(scheme 4)is the best,while the combination of crack welding and inclined under reinforcement steel plate(scheme 5)is the worst.