Health Monitoring Method Of Spatial Structure Bolted Spherical Joint Connection Area Based On Piezoelectric Active Sensing Technology

With the development of infrastructure projects in China,more and more spatial structures are used in public buildings such as terminals,waiting halls,stadiums,etc.Not only are there more and more overall structural forms,but also more and more connection forms between various parts.The connection form of bolted spherical joints is widely used because of its convenient installation,short construction period,and no additional eccentricity.However,during installation and long-term use,there are also some inevitable problems,such as inadequate screwing and environmental erosion,fatigue effects,etc.As a public building,an accident will cause huge casualties and property damage.Therefore,it is of great significance to conduct structural health monitoring on the spatial structure of the bolted spherical joints.Most of the research on the safety of spatial structure is directed to its fatigue failure mechanism and ultimate bearing capacity,while there are few studies on the online structural health monitoring of space structure.Bolt,sleeve damage or external load and interference,so that the stress and connection state of bolted spherical joints are not up to the expected value.Then the problem of node connection failure occurs,using piezoelectric(PZT)ceramic sensors,based on wavelet packet energy analysis method and time reversal method to conduct structural health monitoring on the connection area of the bolted spherical joints.A grid model composed of bolted spherical joints was designed and produced,and experiments were conducted on the model to verify the effectiveness of the above two methods.The specific research contents are as follows:(1)Introduction to the basic principle of structural health monitoring of bolted spherical joint connection area using wavelet packet energy analysis method and the time reversal method,including the working principle of piezoelectric ceramic sensors,theory of contact area of bolt ball joints,the basic theory of wavelet packet energy analysis method and basic theory of time reversal.By simplifying graphics,characteristic analysis and calculation derivation,the method of wavelet packet energy analysis and time reversal to monitor bolted spherical joints were theoretically verified feasibly.This part of the research is the theoretical basis of the whole paper.(2)A bolted spherical joints space grid model was designed,and a verification test was carried out on the model to obtain the axial force of the bolted spherical joint under different torque states.First of all,we introduced the component units of the model,the specifications and material properties of each component.Then,different torques are applied to the connection area to simulate different connection states as the test conditions,and strain gauges are used to measure the connection of the rods under different torques.Strain to obtain the axial force of the connected bar;finally,the corresponding relationship between the torque applied to the sleeve and the axial force of the bar.This relationship provides a basis for the force monitoring of the joint area of the bolted spherical joint based on the wavelet packet energy analysis method and the time reversal method.(3)Taking a reduced-scale bolted spherical joint grid test model as the research object,using piezoelectric ceramic sensor sheets,the effectiveness of the structural health monitoring technology of the bolted spherical joint connection area based on the wavelet packet energy analysis method is verified.The test conditions of applying different torques to the sleeves in the joint area of the bolted spherical joints make the joint area in different tension states.Wavelet packet analysis is performed on the stress waves received by the piezoelectric ceramic sensor under different working conditions,and the corresponding stress wave energy levels were obtained and compared to verify the effectiveness of monitoring the connection status of the bolted spherical joint connection area.Then,according to the relationship between torque and axial force of the bar,the relationship between the energy value and the axial force of the bar is established to verify the effectiveness of the wavelet packet energy analysis method for monitoring the state of the connected area.The energy value is used to calculate the risk index RMSD as an indicator to measure the structure safety.Afterwards,an anti-interference test combined with the BP neural network method was carried out to further improve the recognition accuracy,and verify that the method had certain anti-interference ability.(4)Considering that in the actual monitoring work,the monitoring results will be affected by various noises.In order to improve the noise resistance of the health monitoring method,time reversal technology is further introduced.Taking a reduced-scale bolted spherical joint grid test model as the research object,using piezoelectric ceramic sensors,the effectiveness and noise resistance of the structural health monitoring technology of the bolted spherical joint connection area based on the time reversal method was verified.The test condition is to apply different torques to the connection area.The signal wave is transmitted in the structure,and finally a focused signal with a peak value is formed.Comparing the peak value of the focus signal under different torque states,the effectiveness of the time reversal method for monitoring the connection state of the connection area of the bolted spherical joint was verified.Combined with the relationship between the torque and the force of the rod,the relationship between the peak value of the focus signal and the axial force of the rod was established to verify the effectiveness of the time reversal method for the force monitoring of the connection area.In order to verify the noise resistance of the time reversal method,it can be applied to actual projects.In the test project,the noise conditions were simulated by using metal rod friction rods.The result proved that the time reversal was performed in the presence of external noise interference.The method can still effectively monitor the connection area of the bolted spherical joint.