B. Arun Sundaram

Studies on Apparent Strain Using FBG Strain Sensors for Different Structural Materials

Fiber Bragg grating (FBG) sensors are the most recent type of fiber optic sensors, which are gaining importance in the field of structural health monitoring of civil infrastructure. These are proven to be more versatile due to their distinct advantages such as high sensitivity, immunity to electromagnetic interference, ease of multiplexing, and remote sensing. These are suitable for the long-term monitoring of the structures. The FBG sensors are found to be very effective in strain and temperature sensing. However, the FBG sensors are not self-temperature compensated and the total strain obtained using FBG sensor is the sum of the strain induced due to mechanical load and the apparent strain induced due to temperature. In this article a method to calibrate the apparent strain is discussed. A study is carried out on various structural materials such as mild steel, aluminium, concrete, and carbon fiber-reinforced plastic (CFRP) using bonded and unbounded FBG sensors. This article presents the result in the form of a temperature calibration curve, which can be used to find the actual mechanical strain.

FBG Sensor Technology to Interfacial Strain Measurement in CFRP-Strengthened Concrete Beam

Fiber-reinforced polymer (FRP) composite materials are very attractive for use in strengthening of civil engineering structures because of their high strength to weight and stiffness to weight ratios, being corrosion free, light weight, and potentially high durability. The requirement for any embedded sensor for monitoring strain in FRP-strengthened concrete structures is that the sensor should not be detrimental to the operational requirement of the strengthened structure. Owing to the compatibility with FRP materials, fiber Bragg grating (FBG) sensor is a good choice for embedding at the interface of the FRP-strengthened concrete structures. As the FBG sensors are more flexible and small size (diameter = 250 μm), it may be easily instrumented at the FRP–concrete interface with sufficient surface preparation and suitable adhesive. This article deals with the issues/methods in application of FBG sensors for interfacial strain measurement of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP). It also describes the experimental studies which were carried out to identify the initiation and propagation of debonding of CFRP from concrete surface using FBG array sensors.

Fibre optic sensors as a non-destructive tool for structural monitoring

Structural monitoring is a diagnostic tool for detection of defects/ damages and for scheduling maintenance operations. It is essential to determine the safety of the structures by Non-Destructive Testing (NDT) for evaluation of strength/integrity. This assessment is required for the repair, rehabilitation and life extension of the structure. Fibre Optic Sensors (FOS) are attractive sensing devices as an NDT tool, given their small size, light weight, immune to electrical noise and electromagnetic interference. Optical fibres offer the possibility of embedding in cement/concrete without affecting their performance. Sensors can also be surface mounted on concrete/steel members. There are challenging problems/issues in applying FOS for concrete structures. Systematic studies on FOS have been carried out in the laboratory to solve the issues/problems. In this paper, details of the laboratory studies carried out in solving some of the technical challenges and issues in fibre optic sensing technology are covered.