Reconstructing interfacial force distribution for identification of multi-debonding in steel-reinforced concrete structures using noncontact laser vibrometry

Interfacial debonding in multilayered engineering structures can jeopardize the structural integrity without timely awareness. By reconstructing the distribution of interfacial forces and canvassing local perturbance to the structural dynamic equilibrium, an identification approach for interfacial debonding between different structural components was developed. A "debonding index," governed by the derivatives of reconstructed interfacial forces, was established, able to predict debonding in a quantitative manner including the coexistence of multi-debonding and their individual locations and sizes. The index offers the flexibility of detecting debonding between a beam-like component and its neighboring constituents of any type (beam, plate, shell, or even more complex components) with distinct material properties. To enhance the robustness of the approach under noisy measurement conditions, two denoising techniques (low-pass wavenumber filtering and adjustment of measurement density), together with a data fusion algorithm, were proposed. Using a noncontact laser vibrometry, the approach was validated experimentally by identifying multiple debonding zones in a steel-reinforced concrete slab dismantled from a bridge model. The approach has been demonstrated sensitive to debonding of small dimension owing to the use of high-order differential equation of motion. In addition, it does not require a global model of the entire system, prior information on structural boundaries, benchmark, baseline signals, and additional excitation sources as long as the structure undergoes steady vibration.