Amplitude and phase measurements of continuous diffuse fields for structural health monitoring of concrete structures

P Fröjd,P Ulriksen

doi:10.1016/j.ndteint.2015.10.003

Abstract

Measuring amplitude and phase of continuous ultrasonic waves with a lock-in amplifier is shown to give similarly sensitive indicators of concrete damage as pulsed coda wave analysis, but maintains its sensitivity at considerably much lower signal levels. Continuous and pulsed measurements were performed on a concrete slab subjected to cyclically increased damage level. In the unloaded phase each measurement type was performed at varying transmit signal levels. The result indicates the possibility of using a larger distance between transducers in high frequency health monitoring systems of concrete structures, where attenuation of propagating waves is strong.

Highlights

There is an increasing demand on the reliability and safety of civil structures as these are growing in numbers and getting older
Much effort has been put into developing the fields of non-destructive testing (NDT) and structural health monitoring (SHM)
Like in all ultrasonic measurements, there is a trade-off between range and resolution or sensitivity, and since the aim of the study is to investigate the use of diffuse field measurements in large structures a relatively low frequency was chosen

Summary

Introduction

There is an increasing demand on the reliability and safety of civil structures as these are growing in numbers and getting older. Early warnings of degradation or damage is desired, without invasive test procedures For this reason, much effort has been put into developing the fields of non-destructive testing (NDT) and structural health monitoring (SHM). A major challenge in using the diffuse field is its sensitivity to changes in transducer location and coupling conditions between measurements. This issue is largely circumvented in SHM since the transducers are permanently fixed to the structure. Piezoceramic transducers (PZT) are commonly used, either embedded into the concrete or mounted on the surface These are used both as transmitters and receivers of the mechanical waves and provide an efficient solution for SHM applications. Hammer impact hits, generating strong pulses which can travel relatively far, are not suitable for SHM applications since they are not perfectly reproducible and cannot be used for reciprocal transmission and reception

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Conclusion