The Effcct And Compensation Method Of Temperature And Tension For EMI Damage Detection Technology

Civil engingerring structures in the service process will inevitably be affected by a variety of adverse factors which could result in damage to the structure.The increase of the damage could threaten the safety of the structure.Even worse the structure may be destroyed because of the damage.In order to know the health state of the structures, structural helath monitoing system comes forth. Where damage detection technique based on electro-mechanical impedance(EMI) method with its unique advantages attracted attention of many experts and scholars, and it developed rapiedly in recent years. But EMI based damamge detection technique can be affected by external factores including tempereature and external forces.Based on precvious research, external factors for EMI damage detection technique were studied. In this paper, theoretical analysis, experimental research and data processing were adopted to carry out research work in the following areas:1. The effect of temperature on EMI damaged detection technique wasexploredtheoreticallyby studying the temperature effect on the PZT (Piezoelectric) material parameters. EMI technique for temperature factor was studied experimentally.Admittance curves varitation of different temperature conditions were analyzed. The overall trend of admittance curve remains unchanged as the temperature rised, but the admittance value corresponds to the frequency will be shifted to the left and the peak value becomes large. RMSD damage index of the experimental results were analyzed.It was shown that the change of temperature will cause the change of RMSD index under the same health status. So it may mislead the jugement of structure health status.2. The effect of tension was considered on the basis of the original one-dimensional theoretical model of EMI and the admittance expression was deduced when the structure is under tension condition. The influence of tension on EMI damagedetection technique was analyzed theoretically. Then the experiment of EMI damamge detection technique under tension loads was carried out. Different tension conditions were applied on intect and damaged steel beam respectively. The influence of tension to tension to the admittance cureve and RMSD index was analyzed. The increase of tension will lead to downward shift of admittance cureves, and it will lead to changes in RMSD index. Then the RMSD indexes before and after damage was researched. It shows that the damage of the structure can be detected by RMSD index before and after the damage, but effect of tension can cause misjudgment of structure health status.3. The effective frequency shift (EFS) was adopted to compensate EMI damage detection technique specific to the temperature effect on EMI technique. The admittanceinformation under different temperatures was processing by EFS method. The temperature effect in both the transverse and longitudinal direction was compensated by EFS method. It was shown that RMSD index change caused by temperature is reduced to a certen degree by comparing the RMSD index before and after the compensation. Then EMI damage detection technique joined with EFS compensation method was applied on a practical engineering. EMI technique was adopted to monitoring the health status of a bridge. The PZT transducers were set up on both intect and damage places. The change of admittance and RMSD indexes at different time were researched. After that the admittance information of intect and damage place was processed by EFS. It was shown that the RMSD index after compensation can judge the health status and the damage development effectively.4. The RBF neural nework was adopted to compensate EMI damage detection technique specific to the tension effect on EMI technique. Based on the tension effect experiment, the admittance information of intact beam was used for RBF network training and simulation. The admittance information under different tensions can be predictedby the result of simulation. Then the measured admittance under each tension including intact beam and damaged beam can be compared with predicted value. The health status of the structure can be determined effectively by analyzing the RMSD indexes.