<title>Real-time damage assessment of civil structures using fiber grating sensors and modal analysis</title>

Abstract

In this effort, long gage fiber Bragg grating sensors are used to provide dynamic strain measurements in conjunction with a damage detection algorithm to provide a real-time assessment of the health of a civil structure such as a bridge or a building.Past research in the area of nondestructive damage detection in structures has shown that modal frequencies and modal damping ratios may not be sensitive enough indicators to detect damage, while changes in mode shapes are significantly more sensitive to structural defects or local damage, with the greatest change occurring in the vicinity of the structural defect. In general, local damage conesponds to a local loss of stiffness of some structural element(s). Therefore, damage identification methods based on changes in vibration mode shapes such as changes in mode shape curvature have encountered some success. However, the changes in mode shape curvature are traditionally obtained through double numerical differentiation of "noisy" mode shapes identified using accelerometer data. Thus, the identified mode shape curvatures may be too noisy to identify (i.e., detect, localize, and quantify) low to intermediate level of local structural damage.On the other hand, the effective modal macro-strain vectors used in this effort, which are equivalent to curvature mode shapes, are identified directly from the long-gage fiber grating sensor measurements. Thus, they are in general much less noisy and therefore significantly more reliable than the curvature mode shapes identified using accelerometer data. This is exactly where lies the advantage of using long-gage fiber optic deformation sensors for structural health monitoring and global damage identification of structures.

Development of small-diameter optical fiber sensors and high-speed optical wavelength interrogator for damage detection in composite materials

“…We have recently developed a small-diameter optical fiber with a relative refractive index difference larger than that of the former one 5) . Figure 6 shows the refractive index profiles of small-diameter optical fibers that were estimated from the refractive index profiles of the preforms under the assumption that the diameters of the cores and the claddings of the preforms kept the same ratios after the drawing process.…”

“…FBGs have been used as sensors in a wide range of devices [5][6][7][8] , because they reflect light of a specific wavelength that shifts according to the applied strain or temperature. We developed a FBG sensor with a small-diameter optical fiber whose diameter is less than one-third that of a normal single-mode optical fiber 9) and can thus be embedded in composite materials without inducing any mechanical defects.…”

Development of high-speed optical wavelength interrogation system for damage detection in composite materials

“…1 useful for not only static sensing but also dynamic sensing. Today, many researchers are studying high-speed sensing systems of detecting vibration, acceleration, impact damage, and acoustic emission [5][6][7][8] .…”

Vital Sign Measurement Using Covered FBG Sensor Embedded into Knitted Fabric for Smart Textile

“…It has been applied in monitoring infrastructure state variables [17][18][19][20][21][22]. This system consists of an interrogator (Nagano Keiki co.…”