chapter 1 - Bentham Science

Fiber Bragg Grating Sensors in Civil Engineering Applications Fiber Bragg Grating Sensors 145
Stress(MPa)
700
600
500
400
300
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100
CFRP1
CFRP2
CFRP-FBG1
CFRP-FBG2
0
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Strain(X10 -6 )
(a) (b)
Figure 2: Strength comparison of FRP-FBG bar and FRP bar under loading: (a) CFRP and (b) GFRP.
(a)
(c)
Figure 3: Representative FRP-packaged FBG strain sensors: (a) overall embeddable, (b) end-enlarged, (c) weldable, and
(d) long-gauge.
To address the large-scale nature of infrastructure, an integrated global and local SHM technology with a single OF
was developed by combining the Brillouin Optical Time Domain Analysis/Reflectometry (BOTDA/R) with FBG
sensors. The BOTDA/R and FBG are for distributed and local high-precision strain measurements, respectively. The
combined sensing heads can be easily integrated using the FRP-package method and applied at a length of over
5 km, as depicted in (Fig. 4). (Fig. 5) shows that the strain measured with BOTDA/R is in agreement with that from
FBG (marked with dots) as long as the center wavelength of the FBG is far away from the BOTDA/R’s operation
wavelength of 1550 nm. For practical applications, the BOTDA/R-FBG sensor is installed on a structure so that the
Bragg gratings are located in potential damage areas based on a pre-analysis and assessment of the structure. The
actual location of damage areas and their spatial distribution can be identified by the BOTDA/R measurements,
while the detailed damage data can be acquired through the FBG sensors [14]. (Fig. 6) shows some other metalpackaged
FBG sensors developed by Micron Optics, Inc. (MOI). They are examples of products with the advantages
of fast response time, high accuracy, long-term stability and premium performance under harsh environmental
conditions.
Stress(MPa)
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300
250
200
150
100
50
0
GFRP-FBG1
GFRP-FBG2
GFRP1
GFRP2
-50
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(b)
(d)
Strain(X10 -6 )