Strain Transmission And Cracks Determination Of Structures Under Various Loading Conditions By Distributed Optical Fiber Sensors

Distributed fiber opt ical sensing has huge advantage over other sensing technologies, because it features small size, high accuracy, corrosion and and high temperature resistant, and it can monitor temperature and strain in distribut ion, and it embraces a great potent ial for applicat ion in structural health monitoring.An adhesive and the polymeric coat ing(s) are necessary when the fiber optical sensors are used. The adhesive and the polymeric coat ing(s) would affect the strain transfered from the matrix to the fiber core, and introduce error. Structural members to be measured are usually in complex loading which may include bending, shear, torsion, in addit ion to a uniform axial strain. Therefore, it has an important implicat ion to investigate the strain transmissio n in the protection layers of optical fiber sensor when it is under various loading condit ions. Furthermore, a new method to calculate the w idth of cracks by distributed opt ical fiber sensor is proposed. Detailed researches are summarized as follows.The researches on strain transmission mechanism in protect ion layers o f fibre optical sensors by other researchers are analyzed and summarized. S train transmissio n model of fibre optical sensors under various loading condit ions is developed. The strain transmissio n coefficient is also computed by finite element model, and the strain transmission model is verified by the numerical results.Flanged steel beams and reinforced concrete beams are manufactured as specimens for fibre opt ical sensing test.The fibre opt ical sensors are bonded to the surface of the specimens and embedded into the slots of specimens respectively, and electric resistance strain gauges are also attached to the surface of the specimens for comparison. The specimens are loaded with loads of different patterns, and the strains from strain gauges and fibre optical sensors are read. The rat ios of the two reads are taken as approximat ion to the strain transmissio n coefficients of optical fibers. The influence of loading pattern and the way that the sensors are attached on the strain transfer are observed. Observed is also the influence of the loading intensit y on the strain transfer.The strain distribut ion in the crack zone of concrete beam and fibre opt ical sensor is analyzed. The crack width is calculated by sssuming that the deformat ion of fiber opt ical sensors and concrete beam around the crack is compat ible. A new method to calculate the crack width from the distributed fiber optical sensors is obtained. The method is verified by the experiment results.