| Steel is widely used in various building structures as a kind of material with high strength,lightweight and good plasticity.However,in the process of long-term service,steel structures will suffer from various damages due to environmental corrosion,fatigue and other reasons.In order to prevent damage from expanding and affecting the life of building structures,certain measures need to be taken to strengthen the damaged steel structures.Carbon Fiber Reinforced Polymer(CFRP),as a new type of high-performance material,has the advantages of high strength,strong adaptability and convenient construction.It has been proved that pasting CFRP on the damaged steel structure can significantly improve the strength and fatigue resistance of the damaged structure,delay the crack propagation and improve the service life of the steel structure.Therefore,CFRP strengthening of steel structures has attracted great attention of researchers.The bond interface is the weakest link of CFRP strengthened steel members,and the failure of the bond interface will lead to the debonding of CFRP,which will lead to the destruction of the whole strengthened structure.Therefore,the bond behavior between CFRP and steel plate is one of the key mechanical properties of CFRP strengthened steel structures.Therefore,this paper studies the bond performance and bond-slip relationship of CFRP steel bonding interface.The main research contents are as follows:(1)Tensile test of double-strap CFRP strengthened steel plate.Tensile test of double-strap CFRP strengthened steel plate was carried out.Six groups of 18 double-strap specimens were designed to study the properties of CFRP-steel bonding interface.The failure mode and load-displacement curve of CFRP strengthened steel plate are discussed.Meanwhile,the measured strain data are processed,and the bonding characteristics of the interface of the reinforced specimen are studied.The results show that the thickness of the bonding interface and steel type would affect the failure mode of the bonding interface,and the X100 reinforced specimen is more severely damaged than Q345 B reinforced specimen.Steel type would greatly effect on the ultimate load of the reinforced specimen.The value of the ultimate load of the Q345 B reinforced specimen is about 1.4 times that of the X100 reinforced specimen.The variation of shear strain distribution and shear stress fluctuation at the bonding interface during loading correspond to the expansion of the action scope of CFRP and the debonding of the bonding interface.With the increase of the thickness of the bonding interface,the initial slip and the maximum slip of Q345 B steel specimens both increase,while the maximum shear stress changes little.The maximum interfacial shear stress of Q345 B specimen is about 1.9 times that of X100 specimen.(2)A set of bond-slip model modified formula of CFRP-steel interface.Three existing bilinear bond-slip models are compared.It is concluded that the trend of the fitting results of Xia model with the thickness of the bonding interface is more similar to the test results.According to this model,a set of modified bond-slip calculation models are given.The model is in good agreement with the test results,and the relative error is less than 10%.Secondly,a set of validation tests are designed to verify the accuracy of the modified calculation model.The results show that the bond-slip parameters obtained by the modified formula are also in good agreement with the results of the validation test,and the total error is 10% ～ 12%.(3)Finite element analysis of CFRP-steel bonding interface.The finite element calculation software ABAQUS is used to simulate the tensile test of double-strap CFRP reinforced steel plate.The cohesion model and the maximum stress criterion are introduced into the bonding interface.The bond-slip parameters given by the modified model are substituted into the traction-separation criterion of the cohesion element in the finite element model.After comparing the results of finite element analysis with the experimental result,the validity of the prediction formula and finite element model is verified.Finally,an experimental example is introduced to verify the practicability of the finite element model. |
PDF Full Text Request