Bond Behavior Under Static And Fatigue Load Of Near-Surface-Mounted CFRP To Concrete Structure

NSM CFRP reinforced concrete structure technology is being studied and applied.The bond property of interface between CFRP and concrete is the foundation of the design method of this kind of reinforcement technology.In order to study the static bond behavior and bond-slip relationship of NSM CFRP-to-concrete interface,in the present paper the simple shear pull-out tests were conducted to 22 specimens,which consist of concrete prisms and NSM CFRPs,to investigate the influence of concrete strength,groove width,edge to groove distance,epoxy cover depth,and sectional dimension of concrete on the bond capacity,failure mode,bond stiffness,and bond-slip relationship of NSM CFRP systems.Subsequently a three-segments bond-slip model,containing the residual friction branch,is proposed on the basis of test results.The correlations between the characteristic parameters of the model and the factors such as concrete strength and groove width are analyzed and determined.Based on the above works,a bond-slip constitutive model,which considers the influence of multi-factors of concrete strength,groove width,edge to groove distance for the first time,is established.The simple shear pull-out tests under fatigue load were conducted to 9 specimens.On the basis of the above research,the influence of the upper limit of fatigue load on the bonding performance like failure mode,strain change rule,hysteretic characteristic of embedded CFRP and concrete interface is explored.The S-N model of the interface between CFRP and concrete is proposed and the fatigue limit is predicted.The results show that the factors studied in this paper have a significant influence on static bond of NSM CFRP to concrete.The present bond-slip constitutive model agrees better with test results from literature than the existing models.And the model can be useful for the further research and design of NSM FRP strengthening technique,since the correlation coefficient of the predicted peak bond stress and the actual values from literature is 0.65,suggesting a relatively high accuracy.Small fatigue load amplitude has little effect on the bonding performance of CFRP-concrete interface,and the influence range depends on the stress transfer length of the interface under static loading under the same test force.Under this test condition,when the stress amplitude corresponding to the fatigue load is greater than 127.01 MPa,the fatigue load will greatly weaken the interface bond performance.The strain change rules and fatigue hysteretic characteristic of the bond interface at the loading end,the middle of the bond section and the free end all show different characteristics,which are quite different from the externally bonded CFRP system.