This paper presents the complete test results of a prestressed concrete (PC) beam, including the hydration temperature of the hardening process, the behavior of the PC beam under sustained loading and assessment of damage, such as the locations of cracks and their corresponding depth. Hydration temperatures during the hardening process were determined using fiber Bragg grating (FBG) sensors, while the behavior of the PC beam, under sustained loading, was evaluated and compared using conventional sensors as well as FBG sensors embedded in, or surfaced mounted onto, the PC beam. In addition, a new concept, involving an optical FBG based technique to detect and locate structural damage, such as crack location and depth, is demonstrated.

The exposure and subsequent undermining of pier/abutment foundations through the scouring action of a flood can result in the structural failure of a bridge. Bridge scour is one of the leading causes of bridge failure. Bridges subject to periods of flood/high flow require monitoring during those times in order to protect the traveling public. In this study, an innovative scour monitoring system using button-like fiber Bragg grating (FBG) sensors was developed and applied successfully in the field during the Aere typhoon period in 2004. The in situ FBG scour monitoring system has been demonstrated to be robust and reliable for real-time scour-depth measurements, and to be valid for indicating depositional depth at the Dadu Bridge. The field results show that this system can function well and survive a typhoon flood.

The civil engineering community is becoming increasingly interested in monitoring structural behavior and in assessing its corresponding integration. In this paper, fiber Bragg grating (FBG) sensors were installed to investigate the in situ characteristics of the hydration progress period and the curing process of highway bridge construction. Moreover, the security and serviceability of a bridge can be changed by material proprieties such as shrinkage and creep, which is correlated with the prestressing strain and settlement during the support frame removal. The response and effectiveness of the schedule at every step during the prestressing process, and during the support frame removal, were also examined. It appeared that an FBG sensor was clearly shown to be a smart sensor candidate for function integration and response of a highway bridge during both its construction and service life.

Fiber-Bragg grating (FBG) sensors made on bare fibers are easily damaged when handled improperly during and after fabrication. As a protection from such damage, a novel technique for protecting and packaging FBG sensors has been developed and is presented in this paper. To characterize the strain transmission efficiency of the packaged FBG sensors, an analytical finite-element method is used, and the results are compared with the experiments. It is observed that the thickness and Young's moduli of glues have little influence on the strain transmission, especially when the thickness of the glue is less than the diameter of an optical fiber. However, recoating and steel-tube packaging will markedly affect the strain transmission rate. The strain transmission rates decrease with the increase in thickness of the packaging material. Also, the aging problem of the polymide or acrylate coating and epoxy glue must be considered, since the service life of most structures is usually designed for more than 50 years. The metallic recoated FBG sensor developed in this research uses different approaches, such as low-temperature solder welding, which shows no aging problem, to install the sensors in the structures. Based on the simulated and experimental results, the nickel recoating method is shown to have good strain transmission efficiency compared with other packaging methods.

Embedded optical fiber Bragg grating (FBG) sensors are used to evaluate the properties of high performance concrete (HPC), subjected to high thermal strain. HPC is composed of polypropylene fibers and steel fibers, as additives, in a cylindrical concrete filled steel tube (CFT). A good agreement response between the FBG temperature sensor and a thermocouple was obtained. In addition, experimental results indicate that a CFT behaves differently from unconfined concrete in the center of a specimen, at a furnace temperature of 250 • C and that polypropylene fibers potentially have a higher capability to restrain spalling than do steel fibers.