Detection and characteristics estimation of defects in concrete structures using laser ablation-induced vibration

Abstract

This paper proposes a method for detection and estimation of the characteristics of defects in concrete structures using laser ablation-induced vibration for non-contact structural inspection to prevent partial spalling. Two types of lasers are used: the first is an impact laser that is used to induce vibrations in the measurement target and the second is a detection laser that is used to measure these induced vibrations. Laboratory tests are performed using concrete specimens with and without an internal defect. The results show that the presence of a defect can be estimated from the occurrence of damped oscillations in the measurement data. The presence or absence of these damped oscillations can be determined using the least-squares complex frequency-domain (LSCF) method, which is a fast-stabilizing parameter estimation method for modal identification problems. Additionally, when a defect is present, the defect vibration characteristics, such as natural frequencies and damping ratios, can be estimated. In particular, the natural frequencies can be estimated accurately.