Abstract
This paper investigates the application of distributed optical fiber strain sensors to civil engineering structures, because no other tool can satisfactorily detect the location of the unpredictable phenomenon. In fact, the locations of cracks in the concrete structure are unknown a priori; therefore, a fully distributed sensor is necessary to detect them. The Brillouin optical correlation domain analysis (BOCDA), which offers high spatial resolution by using stimulated Brillouin scattering along the whole length of the optical fiber, is used in a wide range of civil engineering applications, and the same has undergone significant development over the last decade. In this paper, it is demonstrated how a BOCDA-based strain sensor can be employed to monitor cracks in concrete. Crack monitoring on the surface of the concrete member provides useful information for evaluating stiffness and durability of the structure, particularly for early detection of tiny cracks, which is essential for preventing crack growth and dispersion. The crack-induced strain distribution was analytically investigated, and it was proved that BOCDA can identify even a small crack before its visual recognition by a beam test. Moreover, periodical crack monitoring was successfully executed on a pedestrian deck for five years.
Highlights
Degradation of the civil infrastructure has been receiving much attention for a decade in Japan, because a large number of concrete structures are more than fifty years old [1]
This paper investigates the application of distributed optical fiber strain sensors to civil engineering structures, because no other tool can satisfactorily detect the location of the unpredictable phenomenon
The longitudinal strain distribution was measured by a Brillouin optical correlation domain analysis (BOCDA)-based optical fiber sensor with a spatial resolution of 29 mm
Summary
Degradation of the civil infrastructure has been receiving much attention for a decade in Japan, because a large number of concrete structures are more than fifty years old [1]. As a method of Brillouin-based sensors, the Brillouin optical time domain reflectometer (BOTDR) covers a long measurement range by an injected pulse light wave, while Brillouin optical correlation domain analysis (BOCDA) shows high spatial resolution by changing the frequency of two-encountered continuous light waves [3]. Though their advantages and drawbacks are different, both the sensors are good enough to perform SHM in terms of strain distribution measurement. This paper describes the experimental study carried out by using BOCDA to monitor cracks, which were developed in a beam specimen in the laboratory and a bridge deck in the field, by mounting an optical fiber sensor on the concrete surface
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