Abstract
Structural decay of highway bridges is currently an acknowledged worldwide problem. Essentially, highway bridges are a critical integral component of the transportation network, which is vital for sustaining a nationโs socio-economic system. Nevertheless, numerous bridges around the world, including South Africa are structurally deficient. Worse, the severity of the damage present in most of these structures remains unknown, thereby highly imposing socio-economic threats to the nation. Thus, to address these concerns, this research aimed to determine how we can accurately sense the damage present in a bridge structure.
As such, the development of a structural damage sensing system that is based on quasi-distributed long-gauge fibre Bragg grating (FBG) strain sensors, is presented. Owing, to the pitfalls of convectional sensing technologies and the complexities associated with civil structural instrumentation, the use of fibre optics sensors was found to be relevant for this research. While the employment of quasi-distributed strain sensors is not a relatively new concept, research is still necessary for the development of effective structural damage sensing systems for bridges. Review of past literature revealed that, the FBG sensor has attractive sensing attributes. However it still has an inherent limitation which necessitates the need for further research. The limitation is that it can only effectively sense local damage which is at the local point of its placement. To overcome this limitation, our study contributes to the literature by detailing an effective sensor placement optimization strategy for quasi-distributed FBG sensors.
In this study, successful demonstration of the proof of concept is presented initially, through numerical modelling of the sensing system. Subsequently, the characterization and finite element modelling of an identified structural deficient bridge were conducted. Field tests were constituted by vibration sensing, were done to validate the developed model. The validation of the proof of concept, of the damage sensing system, was conducted experimentally in the laboratory through strain tests carried out on the reinforced concrete slab. The experimental set-up consisted of a serial array of wavelength division multiplexed (WDM) FBG sensors, which were coupled to a swept wavelength laser scanning technology system. Lastly, our research contributes by employing the macro-modal strain ratio algorithm (MMSR) as a methodology to detect damage on a real structure. From our findings, which agree well with past literature, we were able to analyze the integrity of the RC slab through analyzing its flexural strain distribution, at a resolution <0.5 ๐๐.