Coda Wave Interferometry Used to Localize Compressional Load Effects in a Concrete Specimen

Abstract : Coda Wave Interferometry (CWI), a method to evaluate subtle changes of elastic wave velocity in a medium, has been proven to be effective to detect small changes or ultrasonic velocity in concrete caused by load, temperature, moisture, damage or other means. While classical CWI is just able to determine velocity changes globally in relatively large areas between and around pairs of transmitters and receivers, several approaches have been proposed to identify the area affected by the changes more precisely. Most of them are based on the calculation of sensitivity kernels for de-correlation of signals measured at a specific state against a reference. Others follow simplified approaches. In a laboratory setup a concrete specimen of 1.5 by 1.5 by 0.5 m m³ was compressed at a certain point by a thread rod, screw nuts and 10 by 10 cm m³ load distribution plates including a load cell to measure the effective load. Maximum loads of 20 to 100 kN (more than one orders of magnitude below the compressive strength of the concrete) have been applied in 5 to 10 kN steps in various cycles. The specimen is equipped with 18 embedded ultrasonic broadband piezo transceivers (60 kHz central frequency). Ten of these receivers have been connected to a multiplexer and ultrasonic transmitting and receiving equipment in a way that allowed almost continuous two way measurements between all sensor pairs. Some of the sensors have been just a few cm away from the center of the load, some almost 1 m. Even simple ways to evaluate the data (e.g. crosscorrelation between signals at different load states) allowed pinpointing the load center at least approximately. A more detailed data evaluation either using CWI or even more one of the more sophisticated localization algorithms gave Òsharperî results in terms of localization and a better correlation between load and velocity change/de-correlation. Referencing the results to the transmitter-receiver pair least affected by load change has led to further improvement. The results are used in upcoming monitoring systems for concrete structures.
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Communication dans un congrès
Le Cam, Vincent and Mevel, Laurent and Schoefs, Franck. EWSHM - 7th European Workshop on Structural Health Monitoring, Jul 2014, Nantes, France. 2014
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Ernst Niederleithinger, Christoph Sens-Schönfelder, Sven Grothe, Herbert Wiggenhauser. Coda Wave Interferometry Used to Localize Compressional Load Effects in a Concrete Specimen. Le Cam, Vincent and Mevel, Laurent and Schoefs, Franck. EWSHM - 7th European Workshop on Structural Health Monitoring, Jul 2014, Nantes, France. 2014. 〈hal-01021036〉

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