The Application Of Embedded Piezoresistive Sensors In The Monitoring Of Concrete Components

Effectively obtaining the performance parameters of civil engineering structures is a key to assess the safety of structures.Existing sensing elements such as strain gauges,strain gauges,fiber gratings,and piezoelectric ceramics have the disadvantages of high cost,poor durability and low sensitivity.Previous studies have shown that rubber-based/cement-based piezoresistive sensors are expected to be applied to the health monitoring field of civil engineering structures due to their superior sensing performance,simple preparation process,long service life,energy saving and environmental protection.At present,the research on the application of rubberbased/cement-based piezoresistive sensors in structural health monitoring stays at the level of sensor elements/lab components.Therefore,improving it to a higher level(laboratory component/actual engineering component)for research has good application significance and practical value.Relying on the static load test of a 25 m maglev track beam and combining the experiment with numerical simulation,this paper mainly studies the application of rubber-based piezoresistive sensors in the intelligent monitoring of concrete columns and the application of cement-based piezoresistive sensors in the intelligent monitoring of maglev track beams.The main contents and conclusions are as follows:(1)The rubber-based piezoresistive sensors of different shapes are embedded in the concrete column under cyclic loading and uniaxial loading to study the piezoresistive performance of the sensors in concrete.The results show that,compared to the cylindrical rubber-based piezoresistive sensor,the flat rubber-based piezoresistive sensor is more suitable for the intelligent monitoring of concrete.It can sense the small strain inside the concrete,and the resistance value has a better match with the stress/strain of the specimen.(2)Through the numerical simulation,the monitoring performance of the flat rubber-based piezoresistive sensor under different electrode materials and sizes,different composite materials and sizes,different concrete materials and sizes,and different working conditions are studied.The influence of the change of sensor parameters on the strength of concrete members is also studied.The results show that the change of sensor parameters has regular effects on its monitoring performance and component strength.In the application,suitable sensor parameters can be selected according to actual needs.Based on the research of experiment and finite element simulation,the application method of rubber-based piezoresistive sensor in concrete internal strain monitoring and collapse warning is proposed.(3)Through numerical simulation,the stress distribution,failure form,concrete damage and crack of 25 m maglev rail beam under loading are analyzed.The placement position of piezoresistive sensor and the stress size of different placement points in each loading stage are identified.On this basis,the intelligent monitoring model of maglev rail beam based on cement piezoresistive sensor is built.(4)Through experiments,the piezoresistive properties of cement-based piezoresistive sensors with different water content and different fillers,and the resistance variation trend of sensors embedded in maglev rail beams and concrete columns,and the resistance variation of sensors in anchorage area before and after prestressed tensioning are studied.The results show that the higher the moisture content of the sensor,the higher the initial resistivity and the maximum resistivity change rate.The resistance of the sensor changes greatly in the first 7 days after embedded concrete,and tends to be stable after 7 days.After prestressing,the cementbased sensor can effectively monitor the stress change of concrete,which shows the effectiveness of the sensor in engineering application.