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.
Recent reports show that modal macro-strain vector (MMSV) obtained by using distributed long-gage FBG sensors is an
effective indicator for damage detection. However, in previous researches, MMSV was always obtained under impulsive
load such as hammer impact. In structural health monitoring of real large-scale structures, however, it is often very
difficult to apply such impulsive load. This paper therefore introduces a new method to abstract MMSV under ambient
excitation. Theoretical deduction reveals that MMSV can be uniquely determined by auto-spectrum of dynamic
macro-strain responses under ambient excitation. Both numerical simulation and experiment were conducted to verify
the proposed methods. Simulation results showed that that the identified frequencies and MMSV vectors under random
excitation are in good agreement with those obtained from theoretical analysis, while experimental results showed the
identified frequencies and MMSV agreed well with those obtained using point impulsive excitation.
In this paper, based on the distributed optical fiber strain sensing technology of pulse-pre-pump Brillouin Optical Time
Domain Analysis (PPP-BOTDA), the creep properties of two types of optical fiber sensors, i.e. single mode optical fiber
with jacket (Type-A) and optical fiber with UV resin coating (Type-B), were studied at different load (60g~600g)
amplitudes. Experimental results show that there exists some creep for both types in initial loading period and tend to
level off with time. But for Type-B, the strain variation is 5% of initial strain, and the stabilization time is about 48h,
both of which are obviously smaller than those of Type-A. As a result, it is revealed that Type-B is characterized by a
smaller creep, suitable for the long-term monitoring of infrastructures.
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
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.
In this paper, the development of carbon fiber-based piezoresistive linear sensing technique and its application in civil
engineering structures is studied and summarized. The sensing mechanism is based on the electrical conductivity and
piezoresistivity of different types of carbon fibers. Firstly, the influences of values of signal currents and temperature on
the sensing properties are studied to decide the suitable sensing current. Then, the linear temperature and strain sensing
feasibility of different types of carbon fibers is addressed and discussed. Finally, the application of this kind of sensors is
studied in monitoring the health of reinforced concrete (RC) and prestressed concrete (PC) structures. A good linearity of
fractional change in electrical resistance (ER) (ΔR/R0)-strain and &DeltaR/R0-temperature is demonstrated. The &DeltaR/R0-strain
and &DeltaR/R0-temperature curves of CFRP/HCFRP sensors can be well fitted with a line with a correlation coefficient
larger than 0.978. All these reveal that carbon fibers reinforced polymer (CFRP) can be used as both piezoresistive linear
strain and temperature sensors.
In this paper, the development and application of smart hybrid carbon fiber reinforced polymers (HCFRPs) are summarized. The active elements of the HCFRPs are carbon fibers/tows in terms of their piezoresistivity and electrical conductivity. Generally, the HCFRPs are divided into two types: HCFRP composites and HCFRP sensors. The HCFRP composites are fabricated with different types of continuous carbon sheets and function as both structural and sensing materials; while, the HCFRP sensors are fabricated with different types of continuous carbon tows and function only as sensing materials. It is shown that before the fracture of carbon fibers/tows the HCFRPs can be used as strain sensors in terms of the piezoresistivity of carbon fibers and after the gradual fractures of different types of carbon fibers they can be used as damage sensors to identify the damage condition of the HCFRPs and HCFRP-strengthened structures.
This paper addresses a novel type of hybrid carbon fiber-reinforced polymer (HCFRP) sensors suitable for the structural health monitoring (SHM) of civil engineering structures. The HCFRP sensors are composed of different types of carbon tows, which are active materials due to their electrical conductivity, piezoresistivity, excellent mechanical properties and resistance to corrosion. The HCFRP sensors are designed to comprise three types of carbon tows-high strength (HS), high modulus (HM) and middle modulus (MM), in order to realize a distributed and broad-based sensing function. Two types of HCFRP sensors, with and without pretreatment, are fabricated and investigated. The HCFRP sensors are bonded with epoxy resins on the bottom concrete surface of RC beam specimens to monitor the average strain, the initiation and propagation of cracks. The experimental results indicate that such kinds of sensors are characterized with broad-based and distributed sensing feasibilities. As a result, the structural health of the RC beams can be monitored and evaluated through characterizing the relationships between the change in electrical resistance of the HCFRP sensors, the average strain and the crack width of the RC beams. In addition, it is also revealed that the damages can also be located by properly adding the number of electrodes.