Implementation of an optical fiber sensor system to monitor the response of reinforced concrete due to formwork removal

Abstract : The movement of a section of a newly constructed reinforced 2-way suspended floor slab in the Department of Civil Engineering Science at the University of Johannesburg was monitored with an embedded optical fiber sensor (OFS) system during and after construction. The sensor system was used to monitor the strain in the structure before, during and after formwork removal. An OFS system was used due to its inherently distinct advantages such as its unobtrusiveness, lightweight and immunity to corrosion. This paper is concentrated on the findings of the results of these strain measurements with emphasis on the use of Fiber Bragg Gratings (FBG). Strain was measured over a 10 month period in a 5 m section of the suspended floor slab. Three periods during the 10 month period were observed. The first stage was showed 128 micro strain experienced by the structure. During the second stage the formwork was removed and large variations were monitored due to excessive external movement around the structure. The third stage indicated a 10 micro strain change. It was found that an OFS system can accurately measure the movement of reinforced concrete, thereby affording the design engineer to opportunity to monitor the structure during and after construction for large movements that can negatively affect the durability and the serviceability of the structure