Damage Identification in Reinforced Concrete Beams Using Spatially Distributed Strain Measurements

Abstract

Brillouin optical time domain reflectometry or analysis (BOTDR/A) is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. Although the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of approximately 1 m. This infers that the technology may lack the ability to identify the exact type and source of damage; that is, different geometrical configurations of cracking within a concrete beam may lead to similar BOTDR/A readings, and hence, the exact nature of cracking might not be resolved. This study suggests different crack indicators and analytically and experimentally examines their correlations with BOTDR/A readings of damaged RC beams. The analytical part entails a finite-element based statistical analysis of hundreds of cracking cases in fractured RC beams and their effects on the simulated BOTDR/A readings. It is found from the analysis that the increase of curvature measured by BOTDR/A is best correlated with the sum of ratios of crack size to the remaining healthy cross section within 1 m. This finding is supported by an experimental study of a cracked RC beam. The correlation, by itself, is only valid when the increase of curvature is associated with the damage and does not involve a curvature increase as a result of redistribution of moments. This, however, would be the case only in statically determinate beams. To facilitate the use of the correlation for statically indeterminate beams, this paper suggests an iterative algorithm that evaluates the different contributors to the increase of the curvature.