Use of fibre-optic (FBG) sensors in structural health monitoring – high grade reinforced concrete beams

Natural disasters such as fires, floods and terrorist activities can cause some critical civil infrastructures to be exposed to extreme loading conditions and/or extreme temperatures. After such exposure these structures may become unsafe for general use. Currently there are limited mechanisms to evaluate the integrity of these structures after such disasters. Fibre Bragg Grating (FBG) Sensors could be used as in-situ sensing systems for reviewing the structural health of these damaged structures. The aim of this research is to design a viable method of embedding FBG Sensors within a concrete structure. This technique will be utilised to analyse the structural health of concrete when curing, under normal operating conditions, and when heated to simulate the extreme condition of a fire. The application will be used to predict damage accumulation and conditions inside the concrete structure before, during, and after such an event. The technique chosen to be tested was to encase FBG Sensors in concrete capsules before embedding them in a concrete structure. It was believed that such a technique would be superior to current and previous methods because it would be flexible and would move with the concrete. This technique thus was compared to an inflexible method of encasing that would encourage crack propagation and prove that FBG Sensors are capable of detecting internal deformities. A reinforced concrete beam was chosen as the structure to be analysed. Three dimensional static and thermal models of the beam were created in Abaqus/CAE. These models were used to determine the locations of the most critical stresses, strains and temperatures. FBG Sensors, as well as thermocouples and strain gauges for result comparison, were then placed throughout the beam structure accordingly as measuring devices. Only replicas of the sensor fibre were able to be successfully embedded in the beam with this unique concrete encasing. This is because the initial design failed. The experimental analysis suggests the modified method that was successfully embedded would be superior to alternate methods of encasing and embedding FBG Sensors, and could be a viable method for industry use. Further work would include the embedding of an actual FBG Sensor encased with the modified method of concrete encasing