Non-invasive Damage Detection in Historic Masonry Walls Using Wavefield Images and Scanning Laser Doppler Vibrometer

Abstract

Even now, optical techniques are inadequate for determining the damage status of historic structures, and this is reflected in national regulations that make reference exclusively to conventional and well-established techniques such as ultrasound, radar, and sonic testing. In this research, we will explore a Structural Health Monitoring (SHM) approach that integrates an image processing technique with the Laser Doppler Vibrometry (LDV) technology for vibration monitoring and assessment of the dynamic properties of stone masonry walls. This combination provides a highly promising contactless method for evaluating the propagation of mechanical body waves and, ultimately, the growth of damage. The fundamental concept is reflected by the well-known fact that the amplitude and velocity of a mechanical wave propagating through a structure are directly impacted by the materials constituting the structure and the existence of damage. Specifically, we offer an integrated signal and image processing technique for detecting damage regions in historical masonry walls utilising wavefield images generated from a regular video camera and wave velocity time histories received from a Laser Doppler Vibrometer (LDV). From the scanned time signals and wavefield images under ambient vibrations and excitation, or normal operating conditions, interactions of mechanical waves are built and analyzed using Operational Modal Analysis (OMA) in order to examine regions of hidden damage. Using the suggested technique, it would be simple to identify damages and changes caused by environmental fluctuations and other physical/mechanical factors.