update WP3 - Assessment and optimization of combined inspection and monitoring strategies
Vibration-based Monitoring (VBM) is a widely used non-destructive approach for monitoring civil infrastructure. Changes in modal characteristics are used for damage detection and localisation. Within a large experimental campaign conducted within WP3, the effects of corrosion damage on different modal characteristics of reinforced concrete beams are studied using data from a lab setup. The beams are subjected to an accelerated corrosion process up to a target corrosion degree of 15%. Modal tests are conducted at 6 evenly spaced moments in time during the corrosion process to identify different modal characteristics (natural frequencies, displacement mode shapes and strain mode shapes). The natural frequencies of the torsional modes decrease strongly due to longitudinal corrosion cracking of the beam. Local corrosion damage is detected and localised using strain mode shapes of the bending modes.
For further reference is referred to https://doi.org/10.1016/j.engstruct.2023.116553.
Evolution of the strain mode shapes of the first bending mode of locally corroded beams. The blue area shows the corroded zone, which is detected and localized using strain mode shapes
In practice, reinforcement corrosion damage and damage induced by mechanical loading both influence the health of reinforced concrete elements. To study the effect of these combined actions, the evolution of the modal characteristics during progressive mechanical load testing of the corroded RC beams is investigated. This distinguishes the present study from the majority of prior vibration-based monitoring studies on mechanically loaded RC beams. Five RC beams are subjected to a four-point bending test. Three of those beams were previously subjected to an accelerated corrosion process, while the other two beams act as reference beams. A smaller reduction in natural frequencies is observed for the corroded beams when compared to the reference beams. In addition, bending cracks occurring within the corroded zones appear to have a smaller influence on the identified strain mode shapes. It can thus be concluded that, if pre-existing corrosion is not properly taken into consideration, damage quantification based on VBM data may therefore result in an underestimation of the damage and overestimation of the load-carrying capacity.
For further reference is referred to https://doi.org/10.1016/j.engstruct.2024.117851.
Reference beam
Uniform corrosion
Local corrosion – symmetrical
Local corrosion – asymmetrical
Crack pattern obtained during the mechanical loading at different load steps. The black cracks were already present before the load test, and result from the corrosion of the longitudinal rebars