Interference and differentiation of the neighboring surface microcracks in distributed sensing with PPP-BOTDA

Abstract

Detection of cracks while at their early stages of evolution is important in health monitoring of civil structures. Review of technical literature reveals that single or sparsely distributed multiple cracks can be detected by Brillouin-scattering-based optical fiber sensor systems. In a recent study, a pre-pump-pulse Brillouin optical time-domain analysis (PPP-BOTDA) system was employed for detection of a single microcrack. Specific characteristics of the Brillouin gain spectrum, such as Brillouin frequency shift, and Brillouin gain spectrum width, were utilized in order to detect the formation and growth of microcracks with crack opening displacements as small as 25 μm. In most situations, formations of neighboring microcracks are not detected due to inherent limitations of Brillouin-based systems. In the study reported here, the capability of PPP-BOTDA for detection of two neighboring microcracks was investigated in terms of the proximity of the microcracks with respect to each other, i.e., crack spacing distance, crack opening displacement, and the spatial resolution of the PPP-BOTDA. The extent of the study pertained both to theoretical as well as experimental investigations. The concept of shape index is introduced in order to establish an analytical method for gauging the influence of the neighboring microcracks in detection and microcrack differentiation capabilities of Brillouin-based optical fiber sensor systems.

Distributed Fiber Optics Sensing and Coda Wave Interferometry Techniques for Damage Monitoring in Concrete Structures

“…Few efforts to apply this model for quantification of crack openings, either on steel [27], aluminum [23,28] or reinforced concrete structures [29], exist in the literature. However, the limitations of the used DFOS systems, in terms of spatial resolution and measurement rate, affected the accuracy of the results.…”

Embedded Distributed Optical Fiber Sensors in Reinforced Concrete Structures—A Case Study

“…Nevertheless, important advances and interesting applications have been conducted recently with the use of Brillouin-based scattering DOFS. From research on crack monitoring in concrete pavements [ 18 ], surface microcracks detection and monitoring [ 19 ], shrinkage induced delamination detection for ultra-high performance concrete (UHPC) [ 20 ] and geotechnical engineering applications in the monitoring of the changes of the concrete curing temperature profile of piles [ 21 ] and soil slope during infiltration monitoring [ 22 ].…”

Distributed Fiber Optic Sensors for Multiple Crack Monitoring in Reinforced Concrete Structures

“…Different interrogation units are available nowadays based on the analysis of the Brillouin and Rayleigh backscattered light all over the silica optical fiber. While it is now well established that these systems have the ability to perform accurate strain measurements and detect the presence of cracks [1][2][3][4], the possibility to quantify the crack openings through the distributed strain measurements has been recently studied [5][6][7][8][9][10].…”

“…Variation of the estimated COD from LVDT and DFOS techniques for cracks(4,7,10) at the Bottom (FO Line7B) and Top (FO Line7T) levels.…”