Research on bolt looseness monitoring based on electromechanical impedance transmissibility technology

Centralized damage, such as bolt looseness, is one of the most common types of damage in bridge structures. Thus, early detection of such damage is essential for bridge maintenance. Detection methods based on transmittance functions (TFs) have been widely studied. These functions use a T matrix to calculate damage indicators and reflect changes in dynamic parameters, such as natural structural frequencies. However, existing research has shown that the excitation position significantly impacts the T matrix. Therefore, this study proposes a new method based on electromechanical impedance (EMI) for local damage characterization, namely, EMI-TF. A series of comparative tests shows that the EMI-TF process is more sensitive and accurate than the traditional TFs. In addition, the sensitivity of the EMI-TF and EMI methods is compared. Results show that using EMI-TF technology can achieve the localization of minor damage at lower frequencies, which, to some extent, overcomes the limitations of the traditional EMI method that can only detect minor damage at high frequencies. The repeatability of EMI-TF is also studied separately in experiments, with ten repeated experiments conducted. Results show that the experimental results of EMI-TF have high repeatability.