Hybrid fibre optic sensor network for real-time high temperature performance monitoring of steel structures

In and post a fire event, an accurate and real-time evaluation and monitoring of a structure’s performance can assist firefighters for efficient survivor rescuing, which significantly improve the fire rescuing safety both for fire fighters and the trapped survivors. However, due to the lack of durable sensors, the structural performance of steel structures in fire conditions is challenging to be evaluated in real time, especially when the associated civil structures are in a large scale. In this paper, a fiber optic sensor network is developed and used to monitor the structural performance of the steel structures in high temperature environments. The fiber optic sensor network has the capacity of real-time large strain measurement up to 12% and temperature of up to 700oC simultaneously. The capability of large strain measurement up to 12% enables the sensor system to monitor the strain distribution of steel structures during fire events in real time. An one-story one-bay steel frame (A36 steel) is used as an example in this paper to perform the structural performance assessment of steel structures in high temperature using the developed sensor network. The simulated fire tests were performed using high temperature furnace through gradual temperature increase from room temperature to 800 °C at a rate of 10 °C/min. The evaluated fiber optic sensor network consists of two long period fiber grating (LPFG) temperature sensors, five movable extrinsic Fabry-Perot interferometric (EFPI) large strain sensors, and two hybrid EFPI/LPFG sensors, which were distributed along the steel frame inside and around the heating zone of the frame. Experimental results demonstrated that the developed sensor network effectively monitored the plastic hinge formation and failure mode of the steel frame, approving the feasibility of the sensor network for steel structure evaluation in high temperature environments.