In this paper, the structural health monitoring of a pre-stressed concrete (PC) structure based on two types of distributed
sensing techniques is addressed. The sensing elements are Brillouin scattering-based fiber optic sensors (FOSs) and
HCFRP (hybrid carbon fiber reinforced polymer) sensors composed of three types of carbon tows. Both types of sensors
are characterized by a broad-based and distributed sensing function. The HCFRP sensors are bonded on PC tendon, steel
reinforcing bar, and embedded in tensile and compressive concrete sides with epoxy resins and putties. The FOSs are
embedded in the tensile and compressive concrete sides where the HCFRP sensors are embedded as well. The distributed
sensors are arranged to detect and monitor the initiation and propagation of cracks, yielding of steel reinforcements and
corrosion of PC tendons. The experimental investigations demonstrate that the initiation and location of cracks, yielding
of steel reinforcements, corrosion of PC tendons and structural health of PC structures can be effectively detected and
monitored with such kinds of distributed sensing systems.
In this paper, the self-sensing and mechanical properties of concrete structures strengthened with a novel type of smart
basalt fiber reinforced polymer (BFRP) bars were experimentally studied, wherein the sensing element is Brillouin
scattering-based distributed optical fiber sensing technique. First, one of the smart bars was applied to strengthen a 2m
concrete beam under a 4-points static loading manner in the laboratory. During the experiment, the bar can measure the
inner strain changes and monitor the randomly distributed cracks well. With the distributed strain information along the
bar, the distributed deformation of the beam can be calculated, and the structural health can be monitored and evaluated
as well. Then, two smart bars with a length of about 70m were embedded into a concrete airfield pavement reinforced by
long BFRP bars. In the field test, all the optical fiber sensors in the smart bars survived the whole concrete casting
process and worked well. From the measured data, the concrete cracks along the pavement length can be easily
monitored. The experimental results also confirmed that the bars can strengthen the structures especially after the
yielding of steel bars. All the results confirm that this new type of smart BFRP bars show not only good sensing
performance but also mechanical performance in the concrete structures.
In general, macro-strain is an effective index for health monitoring of civil infrastructures, which can reveal the
unforeseen damage accumulation. However, it is difficult to acquire precise strain distribution with existing
fully-distributed optical fiber sensing techniques. Based on the distributed optical fiber strain sensing technique of
pulse-prepump Brillouin Optical Time Domain Analysis (PPP-BOTDA), a new optical fiber sensor with improved strain
sensitivity (OFSISS) is proposed to enhance the precision of macro-strain measurements. The most advantage of the
OFSISS sensor is that it can markedly reduce the measurement error of strain data with a proper designed magnified
coefficient. The OFSISS has also good designability and durability according to detailed sensing requirements. Results
of uniaxial tensile experiment show not only the high accuracy and precision of the OFSISS but also an important fact
that the measured magnified coefficients of the manufactured OFSISSs with a recoating process agree well with the
designed values. The bending experiment of using a steel beam illustrates that the linearity and reliability of macro-strain
measurement from the OFSISS are good enough for the application in actual macro-strain monitoring and structural
deformation monitoring.
In this paper, a new type of self-sensing basalt fiber reinforced polymer (BFRP) bars is developed with using the
Brillouin scattering-based distributed optic fiber sensing technique. During the fabrication, optic fiber without buffer and
sheath as a core is firstly reinforced through braiding around mechanically dry continuous basalt fiber sheath in order to
survive the pulling-shoving process of manufacturing the BFRP bars. The optic fiber with dry basalt fiber sheath as a
core embedded further in the BFRP bars will be impregnated well with epoxy resin during the pulling-shoving process.
The bond between the optic fiber and the basalt fiber sheath as well as between the basalt fiber sheath and the FRP bar
can be controlled and ensured. Therefore, the measuring error due to the slippage between the optic fiber core and the
coating can be improved. Moreover, epoxy resin of the segments, where the connection of optic fibers will be performed,
is uncured by isolating heat from these parts of the bar during the manufacture. Consequently, the optic fiber in these
segments of the bar can be easily taken out, and the connection between optic fibers can be smoothly carried out. Finally,
a series of experiments are performed to study the sensing and mechanical properties of the propose BFRP bars. The
experimental results show that the self-sensing BFRP bar is characterized by not only excellent accuracy, repeatability
and linearity for strain measuring but also good mechanical property.
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