Damage Detection Of Orthotropic Plates And Wood Beams Based On The Piezoelectric Impedance

Civil engineering structures are suffering from the erosion of surrounding environment inevitably in the process of long-term service,including the biological,chemical and physical damage.The structures will appear damage and the resistance will decay under the adverse effects.Once the damage of key component accumulates to some degree,the damage will rapidly expand and then the whole structure will fail,causing heavy casualties and economic losses.So it is important for the major civil engineering structures and the key component to make structural health monitoring,especially the early small damage detection.Electromechanical impedance(EMI)technique by using piezoelectric intelligent material has become a new trend,because of its advantages of quick response and high frequency characteristic.On the basis of previous studies,revolving the theme of exploring the feasibility of the fatigue damage monitoring of orthotropic steel bridge panel and the damage location of wooden beam based on EMI,the paper carried out some research from the following several aspects:1.In this paper,a new damage index,Mahalanobis Distance(MD)based RMSD,are proposed.It can be found that the conventional index,root mean square deviation(RMSD)can evaluate damage only in a single frequency band,while the signals of different frequency contain the different damage information.So there are some misjudgements in some frequency when using RMSD index to evaluate the damage extent.Therefore,the paper proposed a more reliable damage index,MD based on RMSD.It can contain more information of different frequency bands,and identify the damage on the whole.It is more sensitive and reliable damage index for structural damage detection based on EMI.2.Experimental study on damage detection of orthotropic plates base on EMI were carried out.In the study,the PZT sensors were attached to the boundary between the plates and U rid and the damage was artificially manufactured.By monitoring the admittance curve before and after damge and computing the corresponding RMSD and MD index,it can be found that the curves can move to the left gradually,and MD index is more reliable to the damage extent than RMSD index.3.Experimental study on fatigue damage monitoring of orthotropic plates based on EMI was carried out.The PZT sensors were attached to the boundary between the plate and U rid and the fatigue load was applied to the model.By monitoring the change of admittance curves before and after loading,it is found that the curves move to the left and the changes were small in the early,and gradually become greater in the middle of loading.It shows that it can identify the damage by monitoring the changes of admittance curves.In order to qualitatively identify the degree of damage,the RMSD index and MD index was established.The results show that MD index is more reliable to the damage extent than RMSD index.4.Exploring the sensing range of PZT in the wooden beam.Multiple PZT were distributed to the wooden beams and damage was made in the study.Then the changes of admittance curves can be monitored.In order to qualitatively identify the degree of changes in the real admittance,the RMSD index was introduced.It can be found that the sensing range of PZT in the wooden beam is 1-1.2 meters.5.Experimental study on damage location of wooden beam based on EMI.Multiple PZT are distributed to wooden beams and damages were made in the study.Then the damage location can be modified by monitoring the changes of admittance curves in the different cases and computing the corresponding RMSD and MD index.It can be found that the sensors near the damage are more sensitive to the damage and the sensors from the damage are less affected.EMI technique is feasible to identify the location of damage.