Evaluation of the Static Load State of Laminated Rubber Bearings Using Electromechanical Impedance

The static load state of bridge bearings is critical to structural safety, yet effective detection methods remain scarce. To address this issue, this study proposes a laboratory evaluation approach based on the Electromechanical Impedance (EMI) technique for assessing the static load condition of laminated rubber bearings. Through static loading tests using the impedance method, the influence of load magnitude, piezoelectric ceramic geometry, and circuit connection on electrical conductance signals was systematically investigated. The load-bearing state was evaluated using statistical indicators derived from conductance frequency spectrum curves. Results demonstrate that the coupled electromechanical impedance of the bearings changes systematically with static loading: the conductance peaks generally increased, with occasional local exceptions, and the Root Mean Square Deviation (RMSD) of the intact sensor increased monotonically, thereby demonstrating the sensitivity of EMI to axial load variations in this laboratory setup. A longitudinally arranged rectangular piezoelectric element exhibited the highest sensitivity among the configurations tested, with a maximum RMSD value of 36.6%, outperforming circular and transversely arranged elements. Within the tested bearings and the applied loading sequence, direct coupling gave the highest sensitivity, while parallel and series connections resulted in reduced responsiveness. Based on these findings, preliminary and indicative RMSD levels are proposed for the intact sensor under controlled laboratory conditions, namely approximately 3.5% and 12.5% for the D250 bearings (corresponding to 2 MPa/90.5 kN and 10 MPa/452 kN, respectively). The study provides a foundational laboratory reference for non-destructive monitoring of bridge bearing health.