Damage assessment of civil engineering structures using distributed optical fiber sensors.

摘要

Integrating work in the fields of failure mechanisms and sensing media, this dissertation focuses on developing a damage assessment method for civil engineering structures using distributed optical fiber sensors (OFSs). Specifically, it investigates stimulated Brillouin-based strain sensors, which are sensitive throughout their length, to detect the debonding of fiber-reinforced polymer (FRP) from concrete as well as cracks in concrete. A method is developed based on theoretical and empirical models that consider both buffering effects for measurements and the optical behavior of stimulated Brillouin scattering. The method is then evaluated experimentally.;If a model of optical signal intensity is adopted where a transient term for stimulated Brillouin scattering is introduced to the existing steady-state term, the Brillouin signal distribution at a specific frequency is sensitive to debonding. Based on this fact, a retrofitted FRP sheet debonding detection method is developed and then evaluated by a four-point bending test. The proposed method is accurate and efficient since it does not require analyzing a cumbersome Brillouin scattering spectrum at the beginning of debonding.;To identify the location and width of cracks in concrete, a strain distribution model is analyzed that takes into account measurement sensitivity within the range of the sensor's spatial resolution. Bending tests are performed on fiber-reinforced concrete (FRC) and successfully demonstrate the sensors' potential to detect invisible cracks as well as the model's validity. Additionally, beam deflection calculations obtained from strain measurements are in well agreement with reference data. One can therefore state that OFSs are capable of both local damage assessment and global integrity monitoring.;Finally, the effects of a fiber's installation upon measurement sensitivity are investigated. The effects of installation are a common issue in OFSs and, with the exception of discrete sensors, only scant literature has been published on the subject. Given the simplified assumption of the sensing fiber component, a strain transfer model for distributed sensors is proposed. The model is experimentally confirmed and is thus deemed useful in determining the method of fiber installation so as to control measurement sensitivity, depending on the purpose.