To solve the survivability of sensing network for life-cycle structural health monitoring, this paper proposes a novel selfhealing
optical fiber sensor network. The self-healing network with link node or emergency component was constructed
and demonstrated by the strain measurement for a three-point bend beam with fiber reinforced polymer-optical fiber
(FRP-OF) sensors and bare optical fiber (OF) sensors. The results show that the stress state of the RC beam can be
successively detected, even some sensors fail or sensing line is broken by using the self-healing sensing network.
Civil Engineers have used fiber reinforced polymer (FRP) with high axial strength as an effective and economical
alternative to steel in harsh corrosion environments. However, the practical applications of FRP are limited by the
tendency of FRP materials to fail suddenly under lateral pressure and surface injury. For example, shear stresses result
from the bonding effect between the FRP material and the structure of the anchorage system due to the lower shear
strength of FRP. This paper proposes a novel smart FRP anchorage system with embedded optical fiber Bragg grating
(FBG) sensors to monitor the axial strain state and accordingly the interfacial shear stress, as well as the interfacial
damage characteristics of FRP anchorage. One FBG sensor was embedded in an FRP rod outside the anchorage region
to evaluate the properties of the material, and seven FBG sensors were distributed along the rod in the anchor to
monitor the axial strain variations and study the interfacial mechanical behaviors of the smart FRP anchorage under a
static pulling load. The experimental results agreed well with theoretical predictions. The smart FRP anchorage system
with optical FBG sensors proves effective and practical for monitoring the long-term mechanical behavior of FRP anchorage systems.
Casing pipes in oil well constructions may suddenly buckle inward as their inside and outside hydrostatic pressure
difference increases. For the safety of construction workers and the steady development of oil industries, it is critically
important to measure the stress state of a casing pipe. This study develops a rugged, real-time monitoring, and warning
system that combines the distributed Brillouin Scattering Time Domain Reflectometry (BOTDR) and the discrete fiber
Bragg grating (FBG) measurement. The BOTDR optical fiber sensors were embedded with no optical fiber splice joints
in a fiber reinforced polymer (FRP) rebar and the FBG sensors were wrapped in epoxy resins and glass clothes, both
installed during the segmental construction of casing pipes. In-situ tests indicate that the proposed sensing system and
installation technique can survive the downhole driving process of casing pipes, withstand a harsh service environment,
and remain in tact with the casing pipes for compatible strain measurements. The relative error of the measured strains
between the distributed and discrete sensors is less than 12%. The FBG sensors successfully measured the maximum horizontal principal stress with a relative error of 6.7% in comparison with a cross multi-pole array acoustic instrument.
KEYWORDS: Wavelets, Denoising, Interference (communication), Optical fibers, Signal processing, Signal to noise ratio, Sensing systems, Optical sensing, Acoustics, Control systems
The signals measured from the Brillouin Optical Time Domain Analysis (BOTDR), distributed optical fiber sensing
system is generally prone to contamination by environmental factors, which may degrade the measurement accuracy in
field applications, a suitable method of correcting this degradation is desired. In this paper, the wavelet signal processing
method is presented to filter out the noise in measured signals and validated with the strain data taken from a smart
BOTDA-based cable. The results show that this method can effectively denoise the information of the measured strain of
the smart cable and improve the precision of the cable force. The maximum error between the control cable force and the
average cable force are 8.8% and 5.1%, respectively, prior to and after noise filtering. This comparison shows that the
wavelet denoising method is suitable for the measured signal obtained from the Brillouin optical sensing system.
Currently, it is difficult to measure the internal forces of steel tie rods under construction and in long-term service. A
novel high-durable smart steel tie rod with functionality of self-monitoring was developed by utilizing fiber Bragg
grating (FBG) and installation techniques combined with glass fiber reinforced polymer (GFRP). The sensing features
for the smart steel tie rod were investigated. The strain obtained from FBG strain sensors shows very good linearity and
repeatability when the steel tie rod is under 85% of its ultimate load. The force calculated from the strain data obtained
during the control loading supports those findings, within a 4% error. This type of smart steel tie rod easily reveals any
stage of stress and can be regarded as a potential strain-based load cell for adjacent structures in a harsh environment.
Traditional point or quasi-distributed sensors can not cover the full scale monitoring of cables in service. A new kind of
smart cable with functionality of full scale monitoring has been developed by combining the optical fiber-fiber
reinforced polymer rebar (named as FRP-OF rebar) with the cable wires by using Brillouin sensing technology. Full
scale cable's static experimental results show that the FRP-OF can discover the stress distribution along the cable under
60% of the ultimate cable loading. And also the repeatability is very good. The cable load gotten from the average
monitored strain agrees well with that from the controlled force within error of 5%. This kind of smart cable shows
perfect advantages such as durability, anti-corrosion, electro-magnetic resistance, low cost and fully-distribution sensing
and so on, which can meet the long-term on-line health monitoring for practical cable.
Brillouin based fiber optic sensing turns to be a promising technology for Structural Health Monitoring (SHM).
However, the bare optical fiber is too fragile to act as a practical sensor, so high durability and large range (large strain)
Brillouin distributed sensors are in great needs in field applications. For this reason, high durable and large range optical
fiber Brillouin Optical Time Domain Analysis (Reflectometer) sensors packaged by Fiber Reinforcement Polymer
(FRP), named BOTDA(R)-FRP-OF, have been studied and developed. Besides, in order to study the large strain, crack
and slip between the rebar and concrete in reinforced concrete (RC) beams using BOTDR(A) technique, five RC Beams
installed with BOTDA(R)-FRP-OF sensors have been set up. And the damage characteristics of the RC beams were
investigated by comparing the strain measured by the BOTDA(R)-FRP-OF sensors and the strain from traditional
electric strain gauges and Fiber Bragg Grating (FBG) sensors, respectively. The test results show that the BOTDA(R)-FRP-OF sensor can effectively detect the damage (including crack and slip) characteristic of RC beam, and it is suitable
for the long-term structural health monitoring on concrete structures such as bridge, big dam and so on.
Brillouin optical time-domain reflectometry (BOTDR) and Brillouin optical time-domain analysis (BOTDA) are considered to be promising and practical sensing techniques for large structures. However, there is still a major obstacle to applying BOTDR or BOTDA on large-scales; the high cost and unreliability associated with sensor installation and failure. We report a novel, low-cost, and highly reliable BOTD sensor using a rebar consisting of a bare optical fiber (OF) packaged in fiber-reinforced polymer (FRP) and named BOTD-FRP-OF. We investigate the surface bonding and its mechanical strength scanning-electron-microscope and intensity experiments. Considering the strain difference between OF and host matrix, which may result in measurement error, the strain transfer from host to OF has been studied theoretically. Furthermore, the sensing properties of glass FRP-OFs for strain and temperature at different gauge lengths were tested under different spatial and readout resolutions using commercial BOTDA. Finally, an absolute dual-BOTD-FRP-OF temperature compensation method is proposed and has been tested. This novel FRP-OF rebar shows both high strength and good sensing properties, which can be used in long-term structural health monitoring for civil infrastructure.
BOTDA(R) sensing technique is considered as one of the most practical solution for large-sized structures as the
instrument. However, there is still a big obstacle to apply BOTDA(R) in large-scale area due to the high cost and the
reliability problem of sensing head which is associated to the sensor installation and survival. In this paper, we report a
novel low-cost and high reliable BOTDA(R) sensing head using FRP(Fiber Reinforced Polymer)-bare optical fiber rebar,
named BOTDA(R)-FRP-OF. We investigated the surface bonding and its mechanical strength by SEM and intensity
experiments. Considering the strain difference between OF and host matrix which may result in measurement error, the
strain transfer from host to OF have been theoretically studied. Furthermore, GFRP-OFs sensing properties of strain and
temperature at different gauge length were tested under different spatial and readout resolution using commercial
BOTDA. Dual FRP-OFs temperature compensation method has also been proposed and analyzed. And finally,
BOTDA(R)-OFs have been applied in Tiyu west road civil structure at Guangzhou and Daqing Highway. This novel FRP-OF rebar
shows both high strengthen and good sensing properties, which can be used in long-term SHM for civil infrastructures.
Distributed Brillouin sensing Technique represents a new physical approach for temperature and strain measurements,
which is based on optical time domain reflectometry (OTDR), and seems extremely promising for Structural Health
Monitoring (SHM) and being received most attention. Due to the intrinsic distributed sensing capability, Brillouin can
measure the temperature and strain using a single-mode fiber, which retains other typical advantages of Fiber Optic
Sensors (FOS). This paper stated the current situation and prospect of distributed Brillouin sensing.
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