Application Of Carbon Nanotube Cement-based Composite Material In Monitoring Of Bridge Bearings

The location of the bridge support is relatively special.As a key component of the bridge to transfer the upper and lower structure loads,long-term load is prone to load fatigue effects,and exposure to the external environment will also adversely affect the durability of the support.Affect the service life of the support.In order to ensure the stable service of the bridge structure,it is very necessary to monitor the stress state of the bridge support and to give timely warning of possible critical situations.Carbon nanotube cement-based composite material is a smart material with good pressure sensitivity.It is made by adding carbon nanotube(CNT)materials with good mechanical,electrical,thermal,and chemical stability to the cement base.Its advantages are convenient construction,lower cost than other optical and electrical sensors,strong adaptability to the environment,and good compatibility with concrete materials.This paper focuses on the analysis of bridge bearing stress state,preparation of CNT cement-based composites,pressure resistivity curve of CNT cement-based composites sensor under different loads and design of monitoring device.(1)Analyze the force of the plate rubber bearing and cushion stone to determine the magnitude of the applied load.Use ABAQUS finite element analysis software to simulate the plate rubber bearing and cushion stone,and find out that it is under different vertical loads and applied The simulation results of the deformation and stress distribution caused by horizontal load thrust are as follows: when the support is subjected to a uniform vertical load,the stress value in the cushion stone is more evenly distributed,mainly concentrated in the corresponding position of the support;in the uneven vertical direction Under load,the bearing on the side with greater compression will produce obvious uneven deformation,and there will also be uneven stress distribution in the cushion stone.The stress value on the side subjected to uneven load is the same and is significantly higher than that on the other side.;When subjected to vertical and horizontal shear,the horizontal deformation of the support is more obvious,and the vertical also produces slight deformation.The force of the cushion stone is the same as that under the uneven load.You can monitor the stress of the cushion stone The load value reflects the bearing state of the support under the action of vertical load.The support will deform under the shear state,and the horizontal force state of the support can also be judged by monitoring this deformation,which provides a basis for the design idea of the support monitoring device.(2)Determine the content of CNT according to relevant literature,and modify the CNT to solve the problem of its dispersion in the cement matrix.In order to facilitate the embedment of the electrode sheet,it was decided to use self-compacting concrete to make the CNT cement-based composite sensor.The test piece was made according to the calculated mix ratio,and the compressive performance test of the test piece was carried out.The compressive strength of self-compacting concrete has been improved to a certain extent,compared with ordinary C50 self-compacting concrete,its compressive strength is increased by 7.5%.The incorporation of modified carbon nanotubes improves the bearing capacity of self-compacting concrete,which can meet the structural strength requirements of the support.The pressure-sensitive performance test of the test piece: under the action of monotonous cyclic load,the pressure-resistivity is linear,showing good recoverability and repeatability,which proves that the carbon nanotube cement-based composite material is used as a support monitoring device The sensor has a certain feasibility.(3)Design a support monitoring device to use the good pressure-sensitive performance of the CNT cement-based to monitor the force state of the support,and to judge the reasonableness of the support during the installation process and whether it is caused by a large load during use When the support is damaged,the corresponding resistivity when the support is broken is given,and the resistivity range of the support under normal working condition is calibrated.