Study Of Box Girder Steel Structure Reinforcement And Typical Fatigue Crack Repairing Using CFRP

Box girder steel structure is a common form in giant steel structures,e.g.port cranes and giant steel bridges.Fatigue failure occurs as it long-term bears heavy-load and fatigue load,which threats safety production and social economy.CFRP(Carbon Fiber Reinforcement Polymer)reinforcement is an advanced nondestructive technology,which owns many advantages including non-injury,easy operation,better reinforcement effective and corrosion resistance.This master thesis focuses on box girder steel structure and typical weld fatigue cracks,applies CFRP material to locally reinforce box girder steel structure and repair typical weld fatigue cracks.Combined with theory analyze,FEM calculating and test verification,locally reinforcement strategy and crack repairing methods are designed,the effectiveness of reinforcement and repairing are evaluated.This thesis has a great value for the further application of CFRP reinforcement technique.The contents of this master thesis are as follows:1)Firstly,basic theories of stress distribution of the interface are introduced,mathematic models including interface shearing force,tensile force and peel stress are established;Based on theory analyze and combined with FEM method,parameters’ influence towards stress distribution are discussed in elastic range,e.g.elasticity modulus of glue and CFRP material,thickness of glue and CFRP material,glue’s length and the shape of edge,excessive glue.2)Secondly,locally reinforcement strategy using CFRP are designed.Under the environment of ANSYS,“CFRP-glue-box girder steel structure” FEM models are set up,compared the carrying capacity,overall stability and locally stress distribution between un-reinforced and reinforced box girder steel structures.Install a three-point bending test to certificate FEM data.3)Lastly,design a method using CFRP material to repair typical weld fatigue cracks,including butt weld zones in lower flange and fillet weld in web plate,combined with secondly development of ANSYS,SIF value of different repairing method are calculated;Via fatigue test of eight specimens of three groups,obtain the cracks propagation rate and fatigue life and compare them with FEM data.By means of the research above,the repairing capability and decent effective of CFRP reinforcement on box girder steel structure are verified.This research has done a further exploration and great contribution to the application of CFRP reinforcement and repairing technology.