| In recent years,bridge overload events have occurred frequently though banned repeatedly.The bridge collapse accident not only endangered the safety of people’s lives and property,but also had a serious adverse impact on society.It should be followed up comprehensively.Traditional traffic monitoring mainly relies on devices such as radar and piezoelectric load cell,which has a high cost,with accuracy and installation conditions affected by many objective environmental factors.The monitoring results of bridge traffic conditions did not achieve the expected effect,and the overload problem was still serious.A carbon nanotube concrete(p-cntc)sensor is made by adding nanofiller(modified carbon nanotube)with a hollow tubular structure into concrete.It has not only excellent mechanical,electrical and pressure-sensitive properties but also has the advantages of low cost,good compatibility with bridge deck structure and sound durability,which shows an exemplary application potential in the field of bridge traffic monitoring.This paper mainly focuses on the design and manufacture of the sensor,the research on the conductivity and pressure sensitivity of the sensor,the pressure-sensitive stability test of the sensor and the simulation application of the overload monitoring system.The main contents are as follows:(1)By consulting the literature and taking into consideration the actual traffic parameters,from the four aspects of sensor material selection,size,electrode material selection and electrode embedding mode,a four-electrode sensor based on self-compacting concrete,with a cross-section size of 4cm×4cm,a height-to-width ratio of 2,and an electrode insertion spacing of 1.5cm was designed..The sensors with electrode materials of copper rod and copper mesh are made,respectively.(2)Conductive and pressure sensitivity tests are performed on sensors with copper rods and copper mesh electrodes..The polarization phenomenon exists in both sensors,and the conductivity of the copper rod electrode sensor is relatively good.Under the action of external cyclic load,the resistivity of both sensors decreases with loading and increases with unloading,which has a good pressure-sensitive response,but the change of resistivity of copper mesh electrode sensor is more obvious than that of copper rod electrode.Overload monitoring applications focused more on pressure-sensitive performance,culminating in the choice of copper mesh electrode sensors.(3)The effects of long-time power on cyclic power off,ambient temperature and humidity on the conductivity and pressure-sensitive stability of the sensor were studied.The cyclic loading test is carried out every two hours.When the total power on time is10 hours,the resistance of the sensor maintains a linear relationship with the load,and the stability of pressure-sensitive reaction is good.After 7 cycles of power on and power off,the linear relationship between sensor resistivity and load is maintained in each test,and the stability of pressure-sensitive response is still good.There is a negative growth relationship between the internal moisture content and the resistivity of the sensor,and the increase of moisture reduces the pressure-sensitive stability of the sensor.The lower the temperature is,the higher the resistivity of the sensor will be.The change in temperature has a slight impact on the pressure-sensitive stability of the sensor,and the origin fitting degree still reaches 0.98.(4)The arrangement of P-cntc sensors on both sides of the bridge deck is more reasonable than that on one side.With the help of wireless transmission measurement equipment developed by the research group,the feasibility of applying P-cntc sensor to overload monitoring was verified through experiments.P-cntc sensor could be applied to bridge deck overload monitoring. |
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