Exploring multiscale nonlinear NDTs for damage detection in concrete structures

It has been shown that non-destructive tests (NDTs) based on nonlinear wave propagation are more sensitive to detecting very small damages in concrete structures than linear techniques. With the aim of exploring the nonlinear effects in civil structures as a damage indicator, we perform a 1-day multiscale vibration monitoring of a test bridge equipped with a pretension system.

We used the pretension system to subject the specimen to eight compression states in its longitudinal direction (400kN at the highest, and 280kN at the lowest). At every compression state, we struck the structure in the vertical direction three times at two locations on the bridge with an impulse source. Throughout the whole experiment, we recorded seismic ambient noise at different frequency bands with a 14-IMU50-sensor array to measure the acceleration and rotation rate, a 14-geophone array with a 4.5 Hz natural frequency, a DAS system, and 4 pairs of ultrasound transducers; the internal temperature of the concrete was also recorded.

At the structural scale (from 1 to 40 Hz) we were able to observe different responses of the structure to pre-tension changes, depending on where the measurement took place in relation to the vertical support pillars by estimating relative velocity changes using the Coda Wave Interferometry stretching processing technique.

At the material scale (ultrasound regime) we can observe temperature-dependent slow dynamics features related to changes in the seismic velocity of the concrete as a consequence of vertical strikes, and its recovery process that returns its physical properties to a steady state after the action of the impulse source.

With this work, we work towards the development of new NDTs that are increasingly sensitive to small cracks and imperfections using conventional and non-conventional seismic instruments to measure linear and nonlinear wave propagation.