Distributed fibre optic sensing: Reinforcement yielding strains and crack detection in concrete slab during column failure simulation

Abstract

Flat slab systems made of reinforced concrete (RC) are popular structural solutions widely used in practical applications. The knowledge about their behaviour under extreme loading conditions, including the loss of the columns, is still being developed worldwide. Also, new materials are tested for this purpose. The research presented hereafter in the article includes the progressive collapse simulation caused by removing the external column in the flat slab system reinforced with B600B steel. One of the aims of the research was to assess the effectiveness of the applied reinforcement after losing the column, depending on the degree of horizontal tie reinforcement. The structural behaviour of the entire reinforced concrete system during the experiment was controlled using advanced reference techniques, including distributed fibre optic sensing DFOS, optical image correlation system, total station as well as conventional strain and displacement transducers. The article focuses on the possibilities of DFOS sensing in an extensive range of strains caused by the steel yielding and the cracks directly in concrete. Thanks to distributed measurements and monolithic composite sensors, it was possible to detect all the cracks and reflect their patterns during all load stages until structural failure. The article describes the methodology and discusses the results of this pioneer measurement approach. Despite the extensive state of the art in distributed sensing, the paper provides the new knowledge gained during research. It is mainly related to a DFOS-based solution for extremely high strain measurements thanks to the excellent bonding properties and strain transfer to the optical fibre, from both steel reinforcement and surrounding concrete.