From Seismology to Bridge Monitoring: Coda Wave Interferometry

Abstract

Concrete is the most widely used building material in the world and its stability assessment is of utmost importance for society. Ultrasonic measurements are one tool for investigation of concrete stability. The goal of those measurements is the derivation of damage sensitive parameters. The way ultrasound diffuses through concrete is affected by cracks in the specimen, so the description of diffusion can show potential damage indicators. Furthermore, the velocity of the wave propagation changes in damaged specimen. With the analysis of the late part of the seismic signal, small velocity changes can be detected and possibly linked to damage. When concrete is loaded, stress and strain change. This is linked non-linearly to velocity changes with the acoustoelastic theory, defining classical and non-classical non-linear parameters as possible damage indicators. In this work, the aforementioned methods and measures are applied to data from loading experiments on specimen of the size and structure of reinforced bridge girders. Ultrasound measurements with embedded sensors, as well as strain measurements were conducted until the girder failed. The analysis shows, that, while the diffusion of ultrasound can be approximated and parameters can be extracted, those parameters are only damage sensitive to some extent and at stages the specimen already shows damages. The velocity changes calculated with coda wave interferometry show a better response when damages appear and local anomalies give information about the location of damaged and extensively strained areas. A link between strain and velocity change shows that the non-linear relation between both measurements can be approximated with a second order polynomial according to the acousto-elastic effect. The parameters of this polynomial are the classical non-linear parameters and accord with literature values. A combination of all three applied methods shows good potential for the setup of a monitoring framework. IDEA League Joint Master's in Applied Geophysics: Delft University of Technology; ETH Zurich; RWTH Aachen University.