Experimental Study On Monitoring Of Loss Of Timber Bolts Based On Piezoelectric Ceramics

In the design demands of pursuing healthy and green life and sustainable development,the modern wooden structure ushered in the spring of development.In order to meet the needs of human production and life and make full use of various profiles,most wood structures need to realize various structural functions through tenon-mortise connection,nail connection and pin connection of components.Existing investigations on the causes of destruction of wooden structures show that about 80% of the wooden structures are destroyed due to the damage of the connecting nodes.Therefore,the connection of the wooden structures occupies a very important position in the design and safety assessment of the wooden structure.Among them,the bolt connection,which is a typical representative of the pin connection,is one of the most important connection methods of modern wooden structure buildings.In this connection method,the bolt preload is a guarantee for a good connection.If the bolt preload can be monitored online in real time,it provides a great guarantee in ensuring the safety of the wooden structure.In this paper,the intelligent piezoelectric ceramic detection technology is used to study the prestressing of the bolts of the wooden structure,the correlation between the stress wave propagation and the prestress is studied by the piezoelectric ceramic wave-transmitting and receiving system,combined with time reversal technology and wavelet packet analysis.The prestress loss index that reflects the tension of the wooden structure bolts is established,which provides a practical method for the health monitoring of the wooden structure bolt pretensioning.The main contents are as follows:First,the application and research status of timber structure nondestructive testing technology are reviewed,the application range of stress wave detection technology in the field of wood structure nondestructive testing and the basic physical characteristics of piezoelectric materials are introduced,and the use of sensing and driving is integrated.The lead zirconate titanate(PZT)can achieve real-time monitoring of the prestress degradation of wood structure bolts.Secondly,the structural damage monitoring methods and theories of piezoelectric ceramics are introduced.The classification of piezoelectric materials,the piezoelectric effect,the relevant characteristic parameters of piezoelectric materials and the related theories of piezoelectric equations are discussed.The ceramic material time reversal technology discusses the specific process of signal transmission when using this method for structural health monitoring,and gives the decomposition process of wavelet transform and wavelet packet transform to the response signal of engineering structure.This lays a theoretical foundation for adopting the energy evaluation index based on wavelet transform and wavelet packet transform.Using pulse signal and sweep signal as excitation,dynamic experiment analysis of pre-tightened bolts was carried out in two groups of 14 situations to obtain the correlation between pre-stress and PZT signal.When the pulse signal was used as the excitation source,eight different bolt prestress values were tested and analyzed.The PZT signal was focused and analyzed by the time reversal method to obtain the peak of the focused signal.The experimental results showed that: The peak value of the focused signal is positively correlated with the bolt prestress.Therefore,a prestress loss index based on wavelet energy rate is constructed to reflect the pretension of the wooden structure.The prestress loss index is linearly related to the prestress of the wooden structure bolts.Based on the above understanding,the sweep signal is used as the excitation signal source to test and analyze six different kinds of bolt prestress,and the prestress loss index is constructed by wavelet packet energy analysis method,which also has the characteristics of positive correlation with the prestress loss of bolt.Based on the essence of stress wave propagation and the fact that bolt prestress can make the connecting wood contact closely with each other,it can be seen that the focused signal obtained by PZT contains the change information of the contact area between the two wood caused by prestress,which can reflect the tightness of bolt prestress.On the other hand,the preload can also make the wood itself compact and strengthen the signal transmission.It can be seen that the active monitoring method based on PZT can be used to monitor the prestress loss of the bolt of the wood structure.The experimental results show that the degradation loss index of wood structure bolt prestress based on wavelet analysis and wavelet packet analysis can accurately evaluate the loss of wood structure bolt prestress.The research in this paper provides the basis for the health monitoring of the prestressed concrete of the bolted connection of wood structure,and gives the specific monitoring indicators.