Crack Monitoring Of Reinforced Concrete Based On PVDF Flexible Strain Sensor

Reinforced concrete structures are prone to produce different types of cracks under the action of environment and load.The development of cracks will lead to the exposure of steel bars,which will rust under the action of the environment,reduce the effective cross-sectional area,and further aggravate the damage of the structure.Therefore,it is extremely important to monitor the development of concrete cracks.At present,the monitoring technology of reinforced concrete structure cracks has the disadvantages of inability to monitor in real time,easy to damage,and small range.This thesis intends to design sensors by measuring strain to monitor the development of cracks in real time.According to the specification,the steel plate reinforcement method can be used to reinforce the steel concrete with cracks.At present,the detection of steel plate reinforcement quality is mainly manual,which has the disadvantages of long detection cycle,large manpower and material consumption.Because the quality of steel plate bonding will affect the conduction of surface stress wave,this thesis uses piezoelectric materials to monitor the stress on the surface of steel plate,so as to monitor the quality of steel plate bonding in real time.The main research contents of this thesis are as follows:(1)The piezoelectric material PVDF(polyvinyl chloride)is pasted on the surface of PDMS(silicone rubber)to make a strip strain sensor.The structural displacement drives the PDMS to stretch,so that PVDF generates a voltage signal.The relationship between the voltage signal and the width and angle of the structural cracking is derived theoretically,and it is further studied by numerical simulation and experiment.The relationship between the charge leakage and the cracking speed of PVDF is designed and tested.The results show that the voltage signal of the strip strain sensor is proportional to the width of the rapid cracking when the bonding angle is determined.The smaller the cracking speed,the more significant the PVDF charge leakage phenomenon.(2)Based on the research of strip strain sensor,an annular crack monitoring sensor is designed.The relationship between the signal output of the annular crack sensor and the crack development is theoretically derived,and further research is carried out through numerical models and experiments.The results show that the sensor can identify the width and direction of cracks for rapid cracks.For cracks that develop slowly,the sensor can identify the cause of crack development,the form of development and the intensity of development.According to the identification signal of the annular crack sensor,the crack damage index B is proposed as the index of the damage of the crack to the structure,and the numerical simulation is studied.(3)The piezoelectric material is used to monitor the quality of the steel plate reinforcement method.The monitoring mechanism of the piezoelectric sensor is deduced.The monitoring effect of the signal generator PZT and the signal receiver PVDF on the quality of the steel plate is studied.The influence of sensor position change on voltage signal is further tested,and its influence mechanism is studied by numerical simulation.The results show that the more serious the damage of the bonded steel plate is,the larger the amplitude of the piezoelectric signal generated by PVDF is.The change of position will lead to the change of stress wave conduction and energy loss,and further affect the piezoelectric signal.