| The strengthened reinforced concrete bridges continue to face the risk of gradual degradation of the remaining bearing capacity and their service life is seriously threatened for the following reasons:1)the continuous overload operation of transportation caused by the excessive pursuit of economic benefits;2)the continuous improvement of design code load grade standards;3)the continuous deteriorate of the material performance and the interfacial bonding performance caused by long-term exposure to harsh service environments such as dry and wet,freeze-thaw,and corrosion.Therefore,the real-time monitoring and reasonable evaluation for the long-term performance and strengthening effect,as well as the preventive secondary strengthening are significant for the strengthened bridges.The prestressed end-anchored CFRP laminate reinforcement technology,which is widely used in the strengthening of the old and dangerous bridges,can significantly increase the strength utilization rate of CFRP materials,and improve the service performance,ultimate bearing capacity and durability of the structures.However,the traditional reinforcement methods are mostly one-time and permanent,and it is difficult to deal with the continuous degradation of the bearing capacity of the reinforced bridge.In response to this problem and the requirements for real-time monitoring and reasonable evaluation of the long-term service performance of the strengthened bridges,this paper focuses on the development of sensors with low-cost and high-durability packaging and layout technology,and the development of secondary strengthening technology,as well as the full-process analysis of the mechanical behavior of the of RC beams strengthened with end-anchored prestressed CFRP plates.The main contents of this paper are as following:Firstly,a smart CFRP laminate embedded with optical fiber bragg grating sensor(OFBG)is developed.The wedge-type anchorage is assembled on the two ends of the smart CFRP laminate using a self-made installation device.The performance test is conducted to obtain the mechanical performance,anchoring efficiency and failure mode,as well as the strain sensing performance index.A three-point bending statical load performance test is carried out on 12 RC beams strengthened with end-anchored OFBG-CFRP smart plates and 1 unreinforced RC beams(coMParative specimens),which verified the full-process test performance of the smart CFRP plate in the laboratory environment;Finally,the OFBG-CFRP laminate is applied on the strengthening project of Dayaowan No.6 Bridge,and the stress evolution pattern of the CFRP plate during the strengthening construction stage and the long-term service stage is obtained,which verifies the reliability and effectiveness of the smart plate in the actual strengthening engineering.Secondly,against the need for real-time monitoring of the in-service strengthened bridges and secondary strengthening,a replaceable OFBG-CFRP laminate-steel plate composite anchorage and the corresponding strengthening system are developed,as well as its anchoring efficiency and failure mode are obtained through static load anchoring tests.Through the limited high-cycle fatigue test of 12 RC beams strengthened with end-anchored prestressed OFBG-CFRP smart plate-steel composite system,the operability of the replaceable composite strengthening system is verified.The improvement effect of replacing the steel plate on the fatigue performance and residual bearing capacity of the reinforced beam was observed,which verified the superiority of the replaceable reinforcement method over the primary reinforcement method from the experimental point of view.Thirdly,the load transferring equation of the end-anchored CFRP laminate-substrate interface under tension load is established.By introducing a dual-exponential bond-slip constitutive model with residual bonding shear stress and a boundary condition where the relative slip at the end of the anchored CFRP plate is 0,the influence of the end anchorage on the interfacial bond slip behavior is simulated.A universal semi-analytical solution for the bond-slip behavior of the end-anchored CFRP plate-substrate interface is deduced.And it is verified by using the existing test data in the literature.The analysis of interface parameters on the axial force,shear stress distribution and load-displacement curve of the end-anchored CFRP-substrate interface during the tensioning process is conducted.Fourthly,based on the semi-analytical solution of the load transferring equation at the end-anchored CFRP plate-substrate interface,the prediction model of the full-scale mechanical behavior and its numerical solution program of an end-anchored CFRP plate strengthened RC beam is established that considers the intermediate crack debonding process using the moment-rotation analysis method based on segment displacement.Fifthly,taking into account the structural characteristics of the replaceable OFBG-CFRP smart plate-steel plate composite strengthening system,the prediction model of the full-process static loading behavior of the RC beam strengthened with the end-anchored prestressed CFRP plate is further expanded.By introducing the performance degradation law of each component material of the strengthened beam under the fatigue load mode,the fatigue behavior,damage factor and residual bearing capacity prediction models during the life of the replaceable composite strengthened beam are established respectively,and their effectiveness and accuracy are verified by the fatigue test results.And then,the evolution of the remaining bearing capacity and damage factor of the composite strengthened beam under different steel plate replacement frequency are analyzed,and the superiority of the replaceable strengthening method over the primary reinforcement method from the theoretical point of view is verified.Finally,a method for evaluating fatigue damage of composite reinforced beams based on the measurements of OFBG-CFRP smart laminates is proposed,and the feasibility of the evaluation process is verified. |
PDF Full Text Request