Health Monitoring Of Carbon Fiber Strengthened Structures By Resistance Response Signals

Based on the long-term health monitoring of carbon fiber reinforced structure,this paper,supported by the natural science fund of Hubei Province,"field self monitoring mechanism of CFRP reinforced bridges"（NO.2016CFB265）,carried out the research on deformation,damage and temperature stress monitoring methods of carbon fiber reinforced structure based on the functional characteristics of carbon fiber reinforced materials.The main research conclusions include:（1）A method for distributed measurement of the deformation of the reinforced structure is established by using the piezoresistivity of the reinforced material.The piezoresistivity of carbon fiber bidirectional braided plate under unidirectional stress was investigated by segmented detection.The experimental results show that the resistance of each segment of the material has a stable force resistance response,and the sensitivity coefficient of each segment is between 3.0 and 3.4.Based on the resistance response of CFRP,the continuous deformation measurement of CFRP strengthened beam structure is carried out.The distribution of resistance change rate of each section of CFRP obtained in the experiment is consistent with the distribution of average axial strain at the bottom of the strengthened beam.（2）A method of layered detection of carbon fiber reinforced concrete structures by using the functional properties of reinforcement materials is proposed,and a virtual simulation experiment is carried out for this method.Based on the finite element model of CFRP strengthened steel beams with prefabricated delamination damage,the potential responses of CFRP strengthened beams with different delamination positions and different delamination lengths under concentrated force are calculated and extracted by using APDL command flow.The damage response sample library of CFRP strengthened beams is established,and the damage position and size are identified by BP neural network technology.The virtual simulation experiment with 16 electrodes verifies the effectiveness of the method for layered detection.（3）The mechanism of temperature stress self detection of CFRP strengthened layer is revealed.It is found that the carbon fiber reinforced concrete（CFRP）plate has NTC effect through heating and cooling experiments;the temperature（stress）change of the structure can be reflected by the strengthened CFRP layer in real time,but its temperature sensitivity coefficient is lower than that before reinforcement.The main reason for the change of temperature sensitive coefficient is that the additional deformation caused by the difference of linear expansion coefficient between the strengthened structure and CFRP offsets part of the temperature sensitive response.The change effect of temperature sensitivity coefficient is verified by theoretical analysis.