Hindawi Publishing Corporation

Advances in Civil Engineering

Volume 2010, Article ID 724962, 13 pages
doi:10.1155/2010/724962

Review Article
Smart Sensing Technologies for Structural Health Monitoring of
Civil Engineering Structures

M. Sun,1 W. J. Staszewski,2 and R. N. Swamy2

1 Department of Engineering Structures and Mechanics, School of Science, Wuhan University of Technology, Wuhan 430070, China
2 Department of Mechanical Engineering, Sheffield University, Sheffield S1 3JD, UK

Correspondence should be addressed to M. Sun, sunmingqing@yahoo.com

Received 31 August 2009; Revised 7 December 2009; Accepted 3 May 2010

Academic Editor: Jinying Zhu

Copyright © 2010 M. Sun et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Structural Health Monitoring (SHM) aims to develop automated systems for the continuous monitoring, inspection, and damage
detection of structures with minimum labour involvement. The first step to set up a SHM system is to incorporate a level of
structural sensing capability that is reliable and possesses long term stability. Smart sensing technologies including the applications
of fibre optic sensors, piezoelectric sensors, magnetostrictive sensors and self-diagnosing fibre reinforced composites, possess very
important capabilities of monitoring various physical or chemical parameters related to the health and therefore, durable service
life of structures. In particular, piezoelectric sensors and magnetorestrictive sensors can serve as both sensors and actuators, which
make SHM to be an active monitoring system. Thus, smart sensing technologies are now currently available, and can be utilized to
the SHM of civil engineering structures. In this paper, the application of smart materials/sensors for the SHM of civil engineering
structures is critically reviewed. The major focus is on the evaluations of laboratory and field studies of smart materials/sensors in
civil engineering structures.

1. Introduction (SHM), which aims to develop automated systems for the

continuous monitoring, inspection, and damage detection
Civil engineering infrastructure is generally the most expen- of structures with minimum labour involvement [2]. An
sive national investment and asset of any country. In effective SHM system can in real time, and online, detect
addition, civil engineering structures have long service life various defects and monitor strain, stress, and temperature
compared with other commercial products, and they are so that the optimum maintenance of the structures can
costly to maintain and replace once they are erected [1]. Fur- be carried out to ensure safety and durable service life.
ther, there are few prototypes in civil engineering, and each In general, a typical SHM system includes three major
structure leads to be unique in terms of materials, design, components: a sensor system, a data processing system
and construction. The most important structures include (including data acquisition, transmission, and storage), and
bridges, high-rise buildings, power utilities, nuclear power a health evaluation system (including diagnostic algorithms
plants, and dams. All civil structures age and deteriorate and information management). The first step to set up
with time. The deterioration is mostly the result of aging of this system is to incorporate a level of stable and reliable
materials, continuous use, overloading, aggressive exposure structural sensing capability. So, this paper is mainly related
conditions, lack of sufficient maintenance, and difficulties to the first component of the SHM system: the sensing system
encountered in proper inspection methods. All of these formed by smart materials/sensors. Smart materials/sensors,
factors contribute to material and structural degradation as such as fibre optic sensors (FOS), piezoelectric sensors, mag-
internal and external damages emerge and coalesce, and then netostrictive sensors, and self-diagnosing fibre reinforced
evolve and progress. structural composites, possess very important capabilities of
To ensure structural integrity and safety, civil structures sensing various physical and chemical parameters related to
have to be equipped with Structural Health Monitoring the health of the structures. Since shape memory alloys and
2 Advances in Civil Engineering

magnetorheological fluids are often used as actuators, they 40

are not introduced in this paper.
FOS, for example, are small and therefore do not 35
affect the performance characteristics of civil engineering
structures in which they are embedded. A single fibre can
efficiently monitor structural performance at various loca- 30
tions by using multiplexed or distributed sensing technolo-
gies. They are unperturbed by electromagnetic interference. 25
Optical waves are suitable for long transmission distances of

Stress (MPa)
relatively weak signals. Piezoelectric and magnetorestrictive
sensors can serve as both sensors and actuators, which 20
make SHM to be an active monitoring system. Furthermore,
they can come in a variety of sizes, allowing them to be 15
placed everywhere, even in remote and inaccessible locations,
to actively monitor the conditions of various types of
10
structures.
Since the subject matter of SHM has been growing
rapidly and significantly over the last few years, the focus of 5
this paper is on a critical state-of-the-art review of various
applications of the above smart materials/sensors in SHM 0
of civil engineering structures. It is beyond the scope of 0 200 400 600 800 1000
the paper to describe all the relevant theories involved, or Strain (microstrain)
to report all of practical applications examples. The paper
covers the major aspects of fibre optic sensors, piezoelectric FOS Vibrating wire
Electrical strain gauge LVDT
sensors, self-diagnosing fibre reinforced composites, and
magnetostrictive sensors for applications in civil engineer- Figure 1: Comparsion of concrete strains with various sesors [8, 9].
ing. Finally, the conclusions of this study are briefly reported.

2. Fibre Optic Sensors (FOSs) well with the output signals obtained from collocated strain
gauge in the test of a concrete cross-beam specimen, and
There are several methods to classify FOS. The first method
FOS had a much better signal-to-noise ratio than the
of classifying FOS is based on the light characteristics (inten-
strain gauge. Quirion and Ballivy [8, 9] have evaluated the
sity, wavelength, phase, or polarization etc.) modulated by
performance of the Fabry-Perot FOS when it was embedded
the parameters to be sensed. The second method classifies
in concrete cylinders. Figure 1 shows the measurements
an FOS by whether the light in the sensing segment is
obtained with FOS compared to those by vibrating-wire
modified inside or outside the fiber (intrinsic or extrinsic).
gauges, electrical strain gauges, and LVDT when the level of
FOS can also be classified as local (Fabry-Perot FOS or long-
stress is slightly over 40% of concrete compressive strength.
gauge FOS etc.), quasidistributed (fibre Bragg grating) and
It can be observed that measured strains with the FOS are
distributed sensors (Brillouin-scattering-based distributed
in good agreement with those measured by the electrical
FOS) depending on the sensing range [3]. This method
strain gauge and LVDT. Zhang et al [10] conducted a
of classification is adopted here. FOS are generally surface
repeated loading test on a concrete slab with embedded FOS.
mounted on existing structures, or embedded in newly
Four million cycles at a frequency of 2 Hz and 3 Hz were
constructed civil structures, including bridges, buildings,
applied. The sensors survived the 4 million loading cycles
and dams, to yield information about strain (static and
at a strain amplitude of 2000 με, and showed good response
dynamic), temperature, defects (delamination, cracks and
to dynamic loading. Delepine-lesoille et al. [11] designed
corrosion), and concentration of chloride ions. The obtained
a kind of composite-made wave-like sensor body, which
data can be used to evaluate the safety of both new-built
could make the stiffness of optical fiber and concrete match
structures and repaired structures, and diagnose location and
to one another. Thus, strain concentrations were reduced,
degree of damages. In this section, the application of FOS
and no theoretical calibration factor had to be taken into
in monitoring of strain, displacement and defects in civil
account. It also achieved continuous bonding to the concrete
engineering structures is reviewed. Other relevant details
and allowed a symmetrical response under tensile and
may be found in early reviews of FOS by Merzbacher et al.
compressive loadings whatever the contact condition was.
[4], Ansari [5] and Leung [6].
Zeng et al. [12] measured the strain distributed along
a 1.65-m reinforced concrete beam using one single-mode
2.1. Monitoring of Strain and Displacement. Laboratory fibre, called as Brillouin-scattering-based distributed FOS
studies have clarified some basic sensing properties of FOS which could measure temperature and strain simultane-
in applications for civil engineering structures. De Vires et al. ously. Strain measurement accuracy reached ± 5 με with the
[7] reported that Fabry-Perot FOS output signals compared resolvable distance of 5 cm. Chen et al. [13] compared two
Advances in Civil Engineering 3

kinds of distributed sensors: Electric Time Domain Reflec- measurements were carried out one year after the opening
tometry cable sensor that was based on the propagation of of the bridge to traffic. Using three 25-ton calibrated trucks
electromagnetic waves in an electrical cable and Brillouin- to evaluate the strain level in the FRP reinforcements, the
scattering-based distributed FOS. They were mounted near measured strains in the FRP reinforcements were less than
the surface of the 80% scale beam-column reinforced 20 με, and strains in the steel girder were less than 120 με.
concrete assembly. Results showed that the cable sensor Mufti et al. [18] described the procedure of embedding FBG
could measure a significant change of strain locally while sensors in the Confederation Bridge, Canada, but no data
distributed FOS were good candidates for the measurement from these sensors have been reported. In Taylor Bridge, a
of slowly-varying strain over a long distance. The cable total of 63 FBG sensors and a total of 26 electric strain gauges
sensor measured a strain distribution in seconds or shorter were bonded to the prestressing CFRP bars to monitor the
and therefore applicable for dynamic signal measurements. maximum strain in the reinforcement due to the applied
However, FOS required several minutes to complete one loads. But even though the strain gauges were properly
measurement. Wu et al. [14] installed Brillouin-scattering- sealed, over 60% of the electric strain gauges malfunctioned
based distributed FOS to evaluate the performance of a due to excessive moisture resulting from steam curing of
full-scale prestressed concrete girder. Compared with the the concrete girders. Strains recorded by FBG sensors were
measurement results from strain gage, FOS gave good results less than 15 με when a 36-ton truck passed the bridge.
for tension strain measurement. But, FOS for compression Besides these, there are some other demonstration projects
strain measurement included a relatively large error, espe- in Canada undertaken by ISIS. More details can be found in
cially when the compression strain was small. http : / / ww.isiscanada.com / field / main.htm ? field projects
In aspect of the practical applications of FOS, Beddington .htm.
Trail Bridge in Calgary, Canada was the first bridge in the Brönnimann et al. [19] reported the application of FBG
world to be monitored by a fibre Bragg grating (FBG) sensing in two bridges in Switzerland. In the Storchenbrucke in
system and the first highway bridge to use carbon fibre Winterthur, FBG were adhered to CFRP wires to measure the
reinforced polymer composite (CFRP) prestressing tendons strain of suspension cables. FBG had been working reliably
in some of its girders. In this bridge, several tendons were within the strain level around 2000 με for three years by
equipped with a total of 18 FBG sensors after prestressing in March 1st, 1999. The other was a pedestrian bridge with
1993 [15]; 15 of sensors survived and functioned correctly. CFRP as the prestressing cable, where the optical fibre was
The relaxation behaviour of prestressing tendons from the embedded in CFRP wire during the pultrusion of CFRP.
combined effects of distressing, concrete creep and shrink- Most of the FBG sensors embedded inside suffered from the
age, dead loads of the bridge deck and the posttensioning high curing temperature of the resin of about 170–190◦ C and
was evaluated. They found that there was a higher net strain the high level prestressing strain of 8000 με, although two
relaxation in the steel prestressed concrete girders than that of them failed due to debonding. They have satisfactorily
in the CFRP tendon, and continuing stress relaxation existed monitored the strain evolution within the cables and the
apparently in all girders eight months after the opening anchor head during the prestressing process and afterwards
of the bridge to traffic. A dynamic truck test showed that for over a year.
these sensors were still operative six years later, and no Inaudi and Vurpillot [20] developed a new method to
structural problems were detected [16]. Above all, the more retrieve the global deformation and curvature of bridges
important significance of their study lies in that this project using their long-gauge SOFO sensors. 96 SOFO, with a
demonstrated the benefits and advantages of merging optic gauge length of 4 m, were embedded in the first two spans
sensing technology, innovative fibre reinforcement materials of the Versoix Bridge. Based on the physical model they
and structural engineering. The real-time monitoring of proposed, global horizontal and vertical deformations of a
FRP reinforcement components can increase user confidence total length of over 100 m were calculated when the static
of their application in concrete structures, since there load was applied on the bridge, and the values matched
are no current design standards for structures with FRP well with that measured by the dial gauges. In a similar
reinforcements. On the other hand, the optic sensors can way, the curvature variations of the Lutrive Highway Bridge
be bonded on the surface of the fibre reinforcement bars with truck circulation were monitored. In addition, field
so that the bars can provide excellent protection of the displacement monitoring was performed in some phases of
sensors and their leads, and yield a very convenient means of construction of the Siggenthal Bridge, such as concreting of
instrumenting and monitoring civil engineering structures different arch, removal of the scaffolding and free standing
in the field. phase of the arch [21].
Currently, many bridges around the world have been Fuhr et al. [22] described the FOS installation process in
instrumented with FOS sensing system. Benmokrane et al. a 67 m long steel truss bridge spanning the Winooski River
[17] applied Fabry-Perot FOS to the rehabilitation project of in Waterbury, Vermont; 46 FOS were embedded in the deck
the Joffre Bridge, Quebec, Canada. They were bonded to the but only one sensor was broken. They [23] have developed
CFRP grids and steel girders to monitor the performance of a frequency-domain-based multiplexing sensor to measure
the FRP reinforced structure, strains of the deck and strains pressure and vibration simultaneously. The hydroelectric
of the girder. The results showed that the temperature was dam on the Winooski River in Vermont was an example
the most important factor influencing the strain variation where this kind of FOS was incorporated into. During the
in the bridge deck under service conditions. The field initial low-power testing of the generation equipment, an
4 Advances in Civil Engineering

abnormal frequency was found, which indicated that a main Crack Optic fibre Magnify 1
gear in the power train was out-of-round [24].
Ou and Zhou [25] reported their work on FOS applied in
1
bridge monitoring in mainland China, especially in Harbin
Institute of Technology. FBG sensors were implemented Concrete specimen
in over 10 practical bridges to monitor strain, stress and Figure 2: The “zig-zag” layout of optic fibre at the bottom of the
temperature. For example, 40 FBG strain sensors, 10 FBG specimen [33]
temperature sensors, and 96 FBG cable sensors have been
successfully installed in Yonghe Bridge in Tianjin City, China.
The strain of the main beam, the stress of the prestressed
reinforcement and the cables were monitored during bridge important contents of the SHM system. The local strain can
load test [26]. Liu and Jiang [27] developed a SHM system be used to detect the working conditions of components. The
for the first cable-stayed bridge across the Yangtze River in data obtained are compared to initial design values of the
China. Both the FBG-based overloading vehicle recognition structures under factored gravity and live loads to examine
system and remote real-time cable force monitoring system if the structures are in the status expected.
operated successfully.
Habel et al. [28] integrated quasi-distributed FOS into 2.2. Detection of Defects. Application of FOS in SHM of
rock anchors to monitor the strain distribution along the civil engineering structures involves detection of defects such
fixed anchor length inside the rock. In order to improve the as cracks, corrosion, and delamination. Crack detection is
stability of the EDER-dam, Germany, a vertical anchoring dependent on loss of optical transmission, and FOS-based
of the dam was performed. The quasi-distributed FOS was ultrasonic wave methods. Detection of corrosion, pH, and
made by inserting fibre splices at regular intervals along chloride content is mainly dependent on colour modulation.
the optical fibre, each segment working as a strain gauge Rossi and Le Maou [32] used optical fibres to monitor
based on time-of-flight measurement. As the anchor was the shape of the crack tip in concrete. The operation of
fabricated, an FOS-equipped aramid rod was placed in the their method was based on the breakage of fibres as a
centre of the anchor. Data from FOS indicated that only crack propagating in concrete reached the optical fibres.
2 to 2.5 m of the fixed anchor length of 10 m contributed However, its use was limited if one did not know crack
to the bond, and this value varied with the changing water location in advance since the polymeric coating of the fibre
level. The sensing system had survived in such a harsh in the cracking zone had to be removed before embedding
environment with anchor forces of 4500 kN. it in concrete. Leung et al. [33] developed a method of
Fiber optic monitoring system has also been introduced monitoring flexural cracks in a concrete beam. The optical
into civil structures under extreme exposure conditions. For fibre was laid in a “zig-zag” form at the bottom of the
example, Newhook et al. [29] have designed a FOS health concrete beam (see Figure 2). When a crack opens in the
monitoring program for the Hall wharf. It was in both the structure, the optical fibre intersecting the crack at an angle
splash and tidal zones, and subjected to thermal ranges of other than 90◦ had to bend. The sudden bending of the
−35◦ C in winter and +35◦ C in summer. Unfortunately the fibre at the crack resulted in an optical power loss. For this
survivability rate of FOS was not high. After the sensors method to work, the fibre should be free to slide inside
were embedded for one year, 10 of the 17 sensors were not the concrete. Preliminary experimental results on concrete
functioning. The main reason for failures of sensors was specimens showed that the proposed approach could detect
associated with connector failures. The manufacturing flaw, the crack opening width as small as 0.1 mm. Recently, their
salt crystals or other dirt caused the failure of the bonding method was used to monitor multiple flexural cracks under
agent holding the connector sheath to the fibre optic cable. static loading, crack monitoring under cyclic loading as well
In general civil buildings, Fuhr et al. [30] installed FOS as the detection of shrink crack under restraint in concrete
in a five-storey, 65000 square feet concrete structure, named beams [34]. However, this method was not feasible to detect
the Stafford Medical Building of Vermont University, to cracks parallel to the surface of the structure. Elvin et al.
monitor stresses incurred during the construction phase [35] proposed a FOSs based technique for the monitoring of
and monitoring of concrete curing as well as internal crack delamination that was parallel to the surface of the structure.
sensing. Kwon et al. [31] used Brillouin-based distributed In their method, a moving load was applied on the measured
FOS to measure temperature distribution in a building beam with one arm of the Servo-Homodyne interferometer
construction. The optical fibre with a length of 1400 m was attached below the surface. The output of the interferometer
installed on the surface of the building. And the temperature represented the optical phase shift and was proportional to
of surface changed normally up to 4◦ C through one day. the integrated strain along the embedded fibre. When the
Among all smart sensors, only FOS have been used position of loading moved, the curve of the phase change
exclusively to monitor so many practical civil structures versus load position could be obtained. It was found that
effectively. These applications show that FOS are more the phase change was very sensitive to both the delamination
promising for SHM of civil engineering structures than location and size.
other smart sensors. Of course, the monitoring of the local Gu et al. [36] employed a quasi-distributed FOS similar
strain of key components of civil engineering structures to that used by Habel et al. [28] for measurement of crack
and displacement of the whole structure is only one of the opening widths along the whole length of reinforced concrete
Advances in Civil Engineering 5

beams under four-point bending. A linear relationship caused the intensity of light propagating through the fibre
between the crack opening width and the loss of the optical to increase. They reported that chloride concentration was
intensity was concluded. It was found that the embedded in proportion to the slope of the light output versus time
FOS could keep a good accounting of the cracks during plots. But the drawback of this sensor was that it was not a
fatigue loading and monotonic loading. reversible sensor, so it was difficult to detect increasing and
FOS can also be utilised as ultrasonic/acoustic sensors decreasing chloride concentrations continuously.
to detect cracks. Chen and Ansari [37] reported a fibre Michie et al. [47] reported a distributed moisture and pH
optic distributed pulse-echo system for monitoring defects detection scheme which used a cable with surface-mounted
in a concrete beam. A PZT transmitter was used for the hydrogel polymer coating and optical fibre. The hydrogel
generation of stress waves. The FOS was adhered to the absorbed water and swelled in aqueous media so that the loss
surface of the beam for sensing the echoed ultrasonic signals. of an optical fibre was modulated. The system was tested in
Preliminary laboratory study showed that this system had a simulated experiment to examine the extent of grout fill
detected two simulated flaws within the beam based on the in a posttensioned concrete structure tendon duct. In their
resonance method. Chen and Farhad [38] developed an FOS experiment, voided regions with no water were identified.
acoustic sensor. It could monitor the acoustic emissions from By selection of the appropriate gel system as the indicator
cracks in a concrete structure. Betz et al. [39] reported that which was responsive to changes in pH, this type of sensor
FBG sensors had the ability to sense ultrasonic Lamb waves. could detect the areas where the pH of the grout dropped.
As a whole, major investigations in this field are pre- The decrease in pH would expose the tendons to potential
liminary laboratory studies. The method proposed by Rossi corrosion. Grahn et al. [48] developed a FOS system for the
and Le Maou [32] requires a priori knowledge of crack measurement of pH in concrete consisting of pH-indicator
location; techniques of Leung et al. [33], and Gu et al. [36] dyes immobilized in a highly hydrophilic polymer matrix.
can perform distributed or quasi-distributed detection of Change in pH was indicated by a colour change of the
cracks which is normal to the fibre direction; the approach of dye/polymer system. The sensor system displayed long-term
Elvin et al. [35] is only for horizontal cracks. Ultrasonic wave stability even in aggressive media of pH 12-13.
methods can work without the limitation of the direction
of crack. Previous studies have exhibited the capability of
ultrasonic waves to detect delamination, voids, and cracks in 2.3. Concluding Remarks of FOS. FOS have the sensing
concrete structures [40–42]. capability both in the laboratory and in the field as local,
With respect to corrosion detection, Fuhr and Huston quasi-distributed (or multiplexed) and distributed sensors.
[43] reported their rebar corrosion detection technique Various applications of FOS in civil engineering structures,
using FOS based on colour modulation. When the fibre such as monitoring of strain, displacement, vibration, cracks,
was in close proximity (<10 mm) to the corroding rebar, corrosion, and chloride ion concentration have been devel-
the input light from the fibre at its end or at a windowed oped. Especially, field tests on bridges, hydroelectric projects,
region was colour modulated. Then the modulated signal and some civil buildings have proved to be effective. FOS
travelled back down the fibre and was sensed via standard can work in the harsh natural environment, and have large
spectroscopy. By comparing the corroded and uncorroded sensing scope, joining with low transmission loss and anti-
spectra, peak wavelength shift along with the intensity of the electromagnetic interference, so they are very advantageous
light signal revealed the presence and the level of corrosion. to perform SHM of civil engineering structures. However,
The experimental result coming from this sensor was in because the study of FOS in civil engineering structures is
agreement with the conventional monitoring methods of relatively recent, and the earliest reports date back only to
steel corrosion. The main limitation of this sensor was its 1989, their long-term sensing ability under field experimen-
small signal-to-noise ratio. Tennyson et al. [44] examined tal conditions due to aging has to be investigated further.
the loop strain of a concrete column using long-gauge FOS They are fragile in some configurations, and the damage is
so that steel corrosion in concrete could be monitored as difficult to repair when embedded. The optical connection
the internal corrosion causes the columns to swell. But, parts, which connect the embedded optical fibre with the
experimental results have not been reported. Wang et al. outer data recording system, are also weak elements of the
[45] made use of the microbending characteristic of long- FOS system. Field examples using FOS to detect defects and
period optical grating (LPFG) to monitor the steel corrosion damages have not yet been fully investigated and reported.
in concrete structures. As the radial expansion of the steel
resulting from the steel corrosion led to the bending of LPFG, 3. Piezoelectric Sensors
the curvature of LPFG could be obtained by analyzing the
change of spectrum, and then the steel corrosion depth could Based on electrical-mechanical transformation, piezoelectric
be measured. This method was independent of the variety materials exhibit simultaneous actuator/sensor behaviour.
in temperature, strain, and refractive index owing to the There are various types of piezoelectric materials: piezo-
inimitable spectrum characteristic of LPFG. electric ceramics, piezoelectric polymers, and piezoelectric
Cosentino et al. [46] developed a fibre optical chloride composites. More recently, piezoelectric sensors were intro-
sensor using Ag2 CrO4 powder bonded to the end of an duced into SHM of civil engineering structures as an active
optical fibre. This sensor worked when the chloride changed sensing technology based on the measurement of electrical
a reddish-brown Ag2 CrO4 to white AgCl. The colour change impedance and elastic waves.
6 Advances in Civil Engineering

3.1. Electrical Impedance-Based SHM Method. When a PZT patches were scanned for the acquisition of the impedance
patch attached to a structure is driven by a fixed, alternating data at various stages during the loading process. The results
electric field, a small deformation is produced in the PZT showed that the surface mounted PZT patches were very
wafer and the attached structure. Since the frequency of sensitive to the development of cracks in concrete in their
the excitation is very high, the dynamic response of the local vicinity, but were insensitive to those farther away.
structure reflects only that of a very local area near the sensor. Tseng and Wang [57] performed two sets of experimental
The response of that local area to mechanical vibration tests on the concrete beams (100 mm ×100 mm × 500 mm)
is transferred back to the PZT wafer in the form of an instrumented with PZT transducers. The root mean-square
electrical response. When a crack or damage causes change deviation (RMSD) of the real part of electric admittance
of the mechanical dynamic response, it is manifested in increased with the progression of damage on the surface of
the electrical impedance response of the PZT wafer [49]. the specimen or in the depth of the specimen. Lim et al. [58]
Therefore, structural damages can be monitored indirectly developed a new method for identifying equivalent structural
through measurement of the electrical impedance of the PZT parameters (stiffness, mass, and damper) from the measured
sensors. admittance signatures, whereby the identified parameters
Ayres et al. [50] bonded two PZT patches to a quarter- were used for damage characterization. The method has been
scale steel truss bridge joint for the acquisition of the applied to detect damages in a truss, a beam and a concrete
electrical impedance when the damage was simulated by cube successfully. Comparing with the conventional RMSD,
loosening bolts in the structure. The real part of admittance their method gave much better insight into the damage
(reciprocal of impedance) was extracted as a function of mechanism whereas RMSD gave little clue about the nature
the exciting frequency. Admittance was sensitive to the of the damage mechanism. While, Wen et al. [59] measured
local damage near the PZT, but was insensitive to damage the equivalent circuit parameters of PZT, such as the static
away from the sensor. Similar tests have been done by compliance, the static resistance, the dynamic inductance,
Park et al. [51]. However, besides the electrical impedance the dynamic resistance, and the dynamic compliance and
method, Park et al. have also used Lamb wave method to so forth, to monitor stress and temperature in concrete
detect damages in a steel bridge component. Park et al. structures.
[52] have monitored the cracking process of a small-scale The impedance method has used a self-sensing actuator
composite-reinforced masonry concrete wall under uniaxial concept: a single PZT acts both as actuator and sensor. The
compression using this method. Besides it, the stability of the qualitative nature of this technique makes it very accessible
impedance-based technique was examined with a civil pipe for everyone, since it does not require any background
joint under significant temperature variation in the range knowledge in order to interpret the simple output. Its sensing
of 25–75◦ C. The impedance changed as temperature varied. area is the vicinity of the sensor, which helps to isolate the
However, when damage was introduced, the temperature effect of damage from other far-field changes in loading, stiff-
made little influence on the qualitative detection result. They ness and boundary conditions. But, it is a qualitative method
[53] also developed a compensation technique to minimise because various types of damage such as cracks, corrosion
the effects of temperature on impedance measurement. The and delamination will all affect the mechanical impedance
compensation procedure was based on the reconstruction similarly, which makes the distinction between each type
of the damage metric, which minimised the impedance of damage very difficult. So, once the impedance-based
drifts due to temperature. Further, Yang et al. [54] studied technique detects damage, other quantitative techniques
the influence of environmental conditions, temperature and have to be used to determine the exact nature of the damage.
thickness of the bonding layer between PZT patches and Otherwise, the impedance analyzers employed are expensive
aluminum plate on the repeatability of electrical admittance until now, an efficient and inexpensive methodology for
signatures. Experimental investigations revealed that under electrical impedance measurement is necessary in the future.
various environmental conditions electrical admittance was
stable for a monitoring period of up to one and a half years.
The effect of bonding could be neglected even for thickness 3.2. Elastic Wave-Based SHM Method. Wang et al. [60] and
up to two-thirds of the PZT patch’s thickness, provided that Wu and Chang [61] conducted preliminary studies to detect
the excitation frequency did not exceed 100 kHz. Above this the debonding between the reinforcing bars and concrete
frequency, the adverse effect of thick (larger than one-third of with PZT patches bonded on the steel rebar. A 5-peak burst
the PZT thickness) bonding was obvious. By comparing the ultrasonic wave with peak value of 200V was applied on the
admittance at the high frequency range (200–1000 kHz), a actuator. Amplitude and time of arrival of the first peak were
temperature change triggered the shift of the PZT resonance recorded and analysed. They found that the amplitude of the
peaks. Some vital experimental observations in [54] have received signals increased in a linearly proportional manner
been successfully verified by means of simulation of the to the debonding size of the steel bar from the concrete. The
PZT–structure interaction using the commercially available arrival time remained constant while the rebar was elastic,
software, ANSYS version 8.1 [55]. but increased as the bar yielded. They [62] also used PZFlex
Soh et al. [56] carried out an impedance-based health software to simulate the response of the sensor as parameters
monitoring and damage detection using PZT patches on a in RC structures such as crack width, size of debonding and
prototype reinforced concrete (RC) bridge. The bridge was position of the rebar varied. Numerical simulation showed
instrumented with 11 PZT patches at key locations. The that cracks in RC structures did not affect the sensor output.
Advances in Civil Engineering 7

When both debonding damage and cracks existed in the P

structures, debonding damage dominated the output signals.
And the depth of the concrete section did not affect the
detection of debonding damage. CFRP Notch
Kawiecki [63] studied the feasibility of nondestructive
damage detection by an array of piezotransducers bonded
(a)
to the surface of a concrete block. Structural damages
were simulated by placing objects with different mass at PZT
the surface of the tested specimens. Experimental results
indicated that there was a strong correlation between the CFRP
size and location of a simulated damage and the variation
of the magnitude of its transfer function and shift of
natural frequency. Anomalies in these signals were repeatable Zone 1 Zone 2 Zone 3
and had distinct characters when they were caused by (b)
damages.
Figure 3: Locations of PZT patches on CFRP bonded on concrete
Saafi and Sayyah [64] developed an active damage inter-
beam [64].
rogation (ADI) technique to detect delaminations between
the repaired concrete and CFRP. As shown in Figure 3,
an array of PZT transducers was attached on to the CFRP 14
laminate. The beam has dimensions of 100 × 150 × 900 mm
with a notch of 10 × 25 × 100 mm to initiate and accel- 12
erate the delamination process. The ADI system actively
10
interrogated the structure through broadband excitation of
Damage index

the transducers. The sensor signals were digitized and the 8

transfer function, cumulative average delta, and damage
index of actuator/sensor pairs were computed. Figure 4 6
shows the relationship between damage index and load. As 4
load increased, the increase of damage index was obvious in
Zone 1, while in Zone 2 and Zone 3 damage index started to 2
increase at 160 kN and 200 kN, respectively. So, the process of
0
delamination was detected. The damage was localized with
1 2 3
an error of 0.67%.
Zone
Sun et al. [65] used PZT patches as sensors or actuators
to initiate and receive Rayleigh waves propagating along No delamination 160 kN
the surface of concrete beam, and longitudinal waves, shear 130 kN 200 kN
waves propagating through internal concrete. Results showed
Figure 4: The variation of damage index for zone 1, 2 and 3 with
that from the velocity of Rayleigh waves and longitudinal applied load increasing [64].
waves, both the dynamic modulus of elasticity and dynamic
Poisson’s ratio of concrete could be calculated. Differences
in amplitude of received waves were highly sensitive to the
cracking process in concrete due to externally applied loads. in reinforced concrete beam were monitored by the encap-
Changes in the waveforms could thus reflect the effects of sulated PZT transducers by Zhao et al. [69]. The damage
internal microcracking in concrete. index calculated according to different central frequency
Song et al. [66] have embedded their smart aggregates elastic wave energy based on continuous wavelet analysis can
containing waterproof piezoelectric patches into different correctly express the initiation and development of crack in
types of concrete specimens. The sensor-history damage the reinforced concrete beam.
index matrix and the actuator-sensor damage index matrix Elastic wave-based approach can detect larger areas than
were obtained to monitor the time-history and location the impedance-based method. Further, the elastic wave-
information of damages in a two-story concrete frame. Their based method can take advantage of more information of the
system could also monitor strength of early concrete and wave propagation to identify damages, such as amplitude and
impact on the structures. Li et al. [67] reported their research phase of the transfer function, shift in frequencies, amplitude
on cement-based 0–3 piezoelectric composites, which had and the arrival time. This method as well as the electrical
good compatibility with concrete and good piezoelectric impedance-based method, is an active sensing method, while
properties. Recently, Lu and Li [68] employed sensors most of the SHM techniques are based on passive sensing
made with cement-based 0–3 piezoelectric composites and diagnostics that rely on passive sensor measurements to
cement-based 1–3 piezoelectric composites to detect the determine changes in the condition or environment of the
acoustic waves due to crack propagation in concrete. Both structure. However, further studies are needed to verify
of them provided good results on the accumulated events the feasibility of piezoelectric sensors monitoring methods
number of the acoustic emission and crack location. Cracks based on ultrasonic wave propagation to detect various
8 Advances in Civil Engineering

×10−3 Table 1: Components of self-diagnosing fibre reinforced compos-

0.6 ites.
0.4 Electrical conductive
Strain

materials and its

0.2
Name of composites Matrix materials
volume content in
the composites
0
0 100 200 300 400 500 Cement, Mortar,
Time (s) Carbon fibre Short carbon fibre concrete including
reinforced concrete (L< 10 mm, <0.5 vol admixtures
(a) (CFRC) %) (methylcellulose,
0.12 silica fume et al.)
0.09
Short carbon fibre
(R − R0 )/R0

Carbon fiber (L < 10 mm,

0.06 reinforced Polymer 10 vol %) Resin, curing agent
0.03
(CFRP) Continuous carbon
fibre (58 vol %)
0 Carbon fiber glass
0 100 200 300 400 500 Continuous carbon
fibre reinforced Resin, curing agent
Time (s) fibre (<0.5 vol %)
Polymer (CFGFRP)
(b) Carbon powder Graphite carbon
dispersed in glass- powders (0.15 vol%,
Figure 5: ΔR/R0 and compressive versus time obtained during fibre-reinforced average particle
Resin, curing agent
cyclic loading for CFRC [70]. plastics (CPGFRP) diameter = 5 μm)
high modulus
defects in real concrete elements and reinforced concrete hybrid carbon fiber (HM), medium
structures by combining other technologies such as wireless reinforced polymer modulus (MM) and Resin, curing agent
communication and algorithms for detection of the positions (HCFRP)sensors high-strength (HS)
carbon tows
of damages and the severity of damages.
L: length

4. Self-Diagnosing Fibre Reinforced Composites

Self-diagnosing (or self-monitoring) fibre reinforced com- Until now, only some small-scale laboratory studies on
posites contain an electrical conductive phase such as carbon smart application of CFRC and CFRP have been conducted.
fibre and conductive powder in the cement or polymer Wen and Chung [75] applied CFRC coatings on the tension
matrix. Table 1 presents the commonly used self-diagnosing and the compression sides of a cement paste beam under
fibre reinforced composites and their components. They flexure. Under cyclic loading and unloading, the resistance
have the abilities to monitor their own strain, damage, and of the coating decreased reversibly on the compression face
temperature. Chen and Chung [70, 71] have reported that in every cycle, while the resistance increased reversibly on the
CFRC can sense strain and damage by its change in electrical tension face in every cycle except the first cycle. So, it appears
resistance. Figure 5 shows the fractional change in resistance that the CFRC strain-sensing coating was a possible usable
along the stress axis as well as the strain during repeated form for SHM of concrete structures. Wang et al. [76] found
compressive loading within the elastic region. Size of mortar the ultimate load and the stiffness of CFRC-strengthened
specimens was 5.1 × 5.1 × 5.1 cm, and the content of short reinforced concrete (RC) beam are slightly larger than that
carbon fibre was 0.24 vol%. As shown in Figure 5, during of the virgin RC beam. Through the measurement of the
the first loading, the irreversibly increasing ΔR/R0 is due electrical resistance change, RC beams with the thicker CFRC
to the weakening of the fibre-matrix interface; during the layer had higher sensitivity to stress and fatigue damage.
second and the subsequent loadings, reversibly decreasing Wang and Chung [77] also applied CFRP coating containing
ΔR/R0 during loading is due to fibre push-in, while reversibly short carbon fibre on cube specimens of mortar to measure
increasing ΔR/R0 during unloading is due to fibre pull-out. the strain. The sensing limits of this sensor were 0–
At high stress amplitude up to failure, resistance increases 420 με in tension and 0–1100 με in compression respectively.
greatly. CFRP has similar properties as CFRC [72]. Mao et Exceeding these limits was found to cause damages in the
al. [73] divided the resistance variation of CFRC with strain coating. It was thus clear that this CFRP coating could not
into three stages: reversible sensing stage, balancing stage satisfy the requirements for practical applications to monitor
(the resistance hardly changes in this phase), and rapidly the performance of concrete structures in real life.
increasing stage, which corresponded to different phases of CFGFRP was designed to be a hybrid of a conductive
crack development in CFRC during loading. Mingqing et carbon fibre with a small ultimate elongation value and an
al. [74] reported Seebeck effect of CFRC, which was the insulating glass fibre with a large ultimate elongation value.
basis of temperature sensing for CFRC and the cement-based As shown in Figure 6, during tensile loading, a distinct
thermoelectric materials. and significant change in electrical resistance indicated the
Advances in Civil Engineering 9

14 30 CFRC containing small volumes of short fibres possesses

12 25 higher stiffness, tensile strength and lower drying shrinkage
10 than plain concrete. Thus the incorporation of carbon fibres
20
R − R0 (Ω)

Load (kN)
8 has not only provided smart abilities, but also improved
15 the mechanical properties of concrete. Laboratory studies
6
10 have shown that they have the abilities to monitor their
4
own strain, damage and temperature. CPGFRP and HCFRP
2 5
have better sensitivity than CFGFRP. However, until now,
0 0 field applications of this kind of smart material in SHM
0 0.5 1 1.5 2
of civil engineering structures have not been developed.
Strain (%)
Further, the sensing repeatability of self-diagnosing fibre
Figure 6: Change in electrical resistance with strain increasing [78]. reinforced composites is needed to improve. There are many
factors that can affect the repeatability of self-diagnosing
fibre reinforced composites, including: (1) distribution state
of conductive materials in the matrix; (2) electrical resistance
failure of carbon tows. After that, CFGFRP does not fracture change due to temperature, moisture, and transversal effect;
suddenly since the load was sustained by the remaining (3) irreversible increase of resistance due to the damages of
high-elongation glass fibres. So CFGFRP had possibilities of the sensing materials and interfaces during cyclic loading;
self-diagnosing function without the occurrence of sudden and (4) methods of resistance measurement and preparation
failure. It can be used to give early-warnings of catastrophic of materials.
failure of structures, and monitor high values of strain
through the use of carbon fibres with different ultimate
elongation values. A CFGFRP grid has been embedded in 5. Magnetostrictive Sensors
the 20th floor slab of the skyscraper known as the Republic
Plaza in Singapore, to detect the occurrence of cracks in Ferromagnetic materials have the properties that, when
concrete. CFGFRP has also been used as a security system placed in a magnetic field, they are mechanically deformed.
for security walls with functions of both detecting and This phenomenon is called the magnetostrictive effect. The
preventing burglaries [78, 79]. reverse phenomenon, in which the magnetic induction of
However, the sensitivity of CFGFRP to strain is very low the material changes when the material is mechanically
in the strain range from zero to the point just before carbon deformed, is called the inverse magnetostrictive effect. Based
fibre fracture. After the breakage of carbon tows, CFGFRP on these phenomena, Kwun and Bartels [83] invented a
can not continue to sense strain or cracks. Therefore, type of magnetostrictive sensor (MsS) which could generate
CFGFRP is generally unsuitable for strain monitoring in the and detect guided waves in the ferromagnetic materials
small or medium strain range. However, CPGFRP (carbon under testing without direct physical contact to the material
powder dispersed in glass-fibre-reinforced plastics) prepared surface. Khazem et al. [84] utilized MsS to inspect suspender
by Muto et al. [80], was superior to CFGFRP with respect ropes on the George Washington Bridge in New York. They
to their capability of monitoring in the above-mentioned launched a pulse of 10 kHz longitudinal guided wave along
strain range. But CPFGRP suffered from difficulties of the length of the suspender, detected the reflected signals
mass production and high cost. While, Yang and Wu [81] from geometric features and defects in the suspender.
employed a new method to improve the sensing capability Na and Kundu [85] used MsS for internal inspection
of CFRP by pulling the impregnated carbon tows repeatedly of voids and inclusions in concrete-filled steel pipes. It was
through a roller with a diameter of 5 cm. Their aim was to shown that the MsS system could generate different guided
preset some microcracks to the carbon tows. Results showed wave modes propagating along the steel pipe; and these waves
that the pretreatment could enhance the sensitivity of CFRP were sensitive to the defects in the pipe. The received wave
to strain more than 100 times, especially in a low strain range. amplitudes decreased as the length of voids and inclusions
Above all, unlike CFGFRP, Yang et al. [82] used three types increased. To overcome the major disadvantage of MsS,
of carbon tows (high modulus, medium modulus, and high- that is, the relatively low ultrasonic energy transmitted, Na
strength carbon tows, resp.) to design hybrid carbon fiber and Kundu [86] developed a hybrid approach combining
reinforced polymer (HCFRP) sensors. HCFRP sensors could PZT and MsS. This method was very effective for steel
monitor the whole loading procedure of concrete structures bar-concrete interface inspection. Bouchilloux et al. [87]
with high sensitivity, including the elastic deformation, the measured the stress of the steel cable based on the reverse
yielding of reinforcing steel bars, and the initiation and magnetostrictive effect. The accuracy of the MsS was within
propagation of cracks in concrete. 3%; but the perturbation of temperature affected the accu-
The technique of SHM using self-diagnosing fibre rein- racy. The difference between two extremes of temperature,
forced composites as sensors is a simple technology. One of that is, between 10◦ C and 50◦ C, was 6%. Rizzo and Di
the most obvious advantages of this type of smart materials Scalea [88] used the discrete wavelet transform to extract
is that they work as both structural materials and sensing damage-sensitive features from the signals detected by MsS
materials. CFRP and GFRP can be used as reinforcing to construct a multidimensional damage index vector. The
elements for concrete, as shown in Section 2 of this paper. damage index vector was then fed to an artificial neural
10 Advances in Civil Engineering

network to provide the automatic classification of the size of practical applications of this type of smart materials in civil
the notch and the location of the notch of multiwire strands. engineering structures are yet to be developed.
MsS can generate different guided wave modes by simply MsS can generate different guided wave modes by simply
changing the coil or magnet geometry. They can work changing the coil or magnet geometry. They can work
without any couplants. Guided waves have strong potentials without any couplants. Guided waves have strong potentials
for monitoring because of the capability for long-distance for structural health monitoring because of their long-
inspections. However, MsS is only suitable for ferromagnetic distance inspection capability. However, it is only suitable
materials. Relatively low ultrasonic energy with low signal for ferromagnetic materials. Relatively low ultrasonic energy
to noise ratio can be transmitted. And the induced energy with low signal to noise ratio can be transmitted.
is critically dependent on the probe proximity to the object SHM system must possess the comprehensive abilities
being tested. to detect positions and severity of damages. However, until
now lots of studies about applications of smart sensors/smart
materials in SHM of civil engineering are related to the basic
6. Concluding Remarks sensing abilities of smart sensors. That is, some damages
within structures can be monitored directly using data from
Smart materials/sensors are a new development with enor- sensors, while others can only be detected indirectly through
mous potential for SHM of civil engineering structures. special diagnostic methods. Important civil engineering
Some of them are currently being applied in the field, while structures are usually very large. So, many sensors are
others are being evaluated under laboratory conditions. equipped to make structures sense their health conditions.
FOS are versatile sensors for SHM applications in civil Wireless transmission and processing the data before trans-
engineering. Various applications of FOS in civil engineering mission will be a useful method to solve the problem of bulk
structures, such as monitoring of strain, displacement, data management in the practical SHM system. And SHM of
vibration, cracks, corrosion, and chloride ion concentration, the practical civil engineering structures will greatly depend
have been developed. In particular, field tests reported on on diagnostic algorithms such as inverse problem analysis,
bridges, hydroelectric projects, and some civil buildings artificial neural network, and the expert system. So, real
have been found to be effective. FOS can work in a harsh SHM system for civil engineering is the integration of smart
natural environment, and have large sensing scope, joining sensors/smart materials, data transmission, and advanced
with low transmission loss, antielectromagnetic interference diagnostic methods.
and distributed sensing, and so they are advantageous to
apply for SHM of civil engineering structures. However, the
long-term sensing ability of FOS under field experimental Acknowledgments
conditions due to aging has not been fully established, and
needs to be investigated further. They are fragile in some The authors would like to acknowledge the Chinese Schol-
configurations, and the damage is difficult to repair when arship Council (CSC) for the financial support to the first
embedded. The optical connection parts, which connect the author during his research study at Sheffield University in
embedded optical fibre with the outer data recording system, UK. The work is also supported by the National Natural
are also weak elements of the FOS system. Field examples Science Foundation of China (no. 50878170) partly.
using FOS to detect defects and damages have not yet been
fully investigated and reported.
References
Piezoelectric sensors can be used as an active sensing
technology in the SHM of civil engineering structures [1] K. P. Chong, “Health monitoring of civil structures,” Journal
based on electrical impedance and elastic wave methods. of Intelligent Material Systems and Structures, vol. 9, no. 11, pp.
The impedance method depends on the self-sensing actu- 892–898, 1999.
ator concept. It is a qualitative method. Elastic wave- [2] F. K. Chang, “Structural health monitoring: a summary report
based approaches can detect larger areas of damage than on the first international workshop on structural health
the impedance-based method, and this method can take monitoring,” in Proceedings of the 2rd International Workshop
advantage of additional information arising from the wave on Structural Health Monitoring, F. K. Chang, Ed., pp. 3–11,
propagation to identify damages. However, further studies Technomic Publishing Company, Lancaster, UK, September
1997.
have to be carried out to verify the feasibility of this method
[3] B. Culshaw and J. Dakin, Eds., Optical Fiber Sensors. Appli-
to detect various defects in real concrete structures and
cations, Analysis, and Future Trends, vol. 4, Artech House,
reinforced concrete structures. London, UK, 1996.
Self-diagnosing fibre reinforced composites are also [4] C. I. Merzbacher, A. D. Kersey, and E. J. Friebele, “Fiber optic
available as sensors and offer a very simple technology for the sensors in concrete structures: a review,” Smart Materials and
SHM of civil engineering structures. One of the most obvious Structures, vol. 5, no. 2, pp. 196–208, 1996.
advantages of this type of smart materials is that they work as [5] F. Ansari, “State-of-the-art in the applications of fiber-optic
both structural materials and sensing materials. Laboratory sensors to cementitious composites,” Cement and Concrete
studies have shown that they have the abilities to monitor Composites, vol. 19, no. 1, pp. 3–19, 1997.
their own strain, damage and temperature. CPGFRP and [6] C. K. Y. Leung, “Fiber optic sensors in concrete: the future?”
HCFRP have better sensitivity than CFGFRP. However, the NDT and E International, vol. 34, no. 2, pp. 85–94, 2001.
Advances in Civil Engineering 11

[7] M. De Vries, M. Nasta, V. Bhatia et al., “Performance of [21] D. Inaudi, A. Rufenacht, B. Von Arx, H. P. Noher, S.
embedded short-gage-length optical fiber sensors in a fatigue- Vurpillot, and B. Glisic, “Monitoring of a concrete arch bridge
loaded reinforced concrete specimen,” Smart Materials and during construction,” in Smart Structures and Materials: Smart
Structures, vol. 4, no. 1A, pp. 107–113, 1995. Systems for Bridges, Structures, and Highways, vol. 4696 of
[8] M. Quirion and G. Ballivy, “Concrete strain monitoring with Proceedings of SPIE, pp. 146–153, San Diego, Calif, USA,
Fabry-Pérot fiber-optic sensor,” Journal of Materials in Civil March 2002.
Engineering, vol. 12, no. 3, pp. 254–261, 2000. [22] P. L. Fuhr, D. R. Huston, M. Nelson et al., “Fiber optic sensing
[9] M. Quirion and G. Ballivy, “Laboratory investigation on of a bridge in Waterbury, Vermont,” Journal of Intelligent Mate-
Fabry-Pérot sensor and conventional extensometers for strain rial Systems and Structures, vol. 10, no. 4, pp. 293–303, 2000.
measurement in high performance concrete,” Canadian Jour- [23] P. L. Fuhr and D. R. Huston, “Multiplexed fiber optic pressure
nal of Civil Engineering, vol. 27, no. 5, pp. 1088–1093, 2000. and vibration sensors for hydroelectric dam monitoring,”
[10] B. Zhang, B. Benmokrane, J.-F. Nicole, and R. Masmoudi, Smart Materials and Structures, vol. 2, no. 4, pp. 260–263,
“Evaluation of fibre optic sensors for structural condition 1993.
monitoring,” Materials and Structures, vol. 35, no. 250, pp. [24] D. R. Huston, P. L. Fuhr, T. P. Ambrose, and D. A. Barker,
357–364, 2002. “Intelligent civil structures—activities in Vermont,” Smart
[11] S. Delepine-Lesoille, E. Merliot, C. Boulay, L. Quétel, M. Materials and Structures, vol. 3, no. 2, pp. 129–139, 1994.
Delaveau, and A. Courteville, “Quasi-distributed optical [25] J. Ou and Z. Zhou, “Applications of optical fiber sensors
fibre extensometers for continuous embedding into concrete: of SHM in infrastructures,” in Smart Sensor Phenomena,
design and realization,” Smart Materials and Structures, vol. 15, Technology, Networks, and Systems, vol. 6933 of Proceedings of
no. 4, pp. 931–938, 2006. SPIE, p. 10, San Diego, Calif, USA, March 2008.
[12] X. Zeng, X. Bao, C. Y. Chhoa et al., “Strain measurement [26] C. Lan, Z. Zhou, S. Sun, and J. Ou, “FBG based intelligent
in a concrete beam by use of the Brillouin-scattering-based monitoring system of the Tianjin Yonghe Bridge,” in Smart
distributed fiber sensor with single-mode fibers embedded Sensor Phenomena, Technology, Networks, and Systems 2008,
in glass fiber reinforced polymer rods and bonded to steel vol. 6933, article 693312 of Proceedings of SPIE, p. 9, San
reinforcing bars,” Applied Optics, vol. 41, no. 24, pp. 5105– Diego, Calif, USA, March 2008.
5114, 2002.
[27] S. Liu and D. Jiang, “The application of structural health mon-
[13] G. Chen, B. Xu, R. D. McDaniel, X. Ying, D. J. Pommerenke,
itoring system technology FBG-based to no.2 Wuhan bridge
and Z. Wu, “Distributed strain measurement of a large-
over Yangtze river,” in Photonics and Optoelectronics Meetings:
scale reinforced concrete beam-column assembly under cyclic
Fiber Optic Communication and Sensors (POEM ’08), vol. 7278
loading,” in Smart Structures and Materials: Sensors and Smart
of Proceedings of SPIE, Wuhan, China, November 2008.
Structures Technologies for Civil, Mechanical, and Aerospace
[28] W. R. Habel, I. Feddersen, and C. Fitschen, “Embedded quasi-
Systems, vol. 5765, article 55 of Proceedings of SPIE, pp. 516–
distributed fiber-optic sensors for the long-term monitoring
527, San Diego, Calif, USA, March 2005.
of the grouting area of rock anchors in a large gravity dam,”
[14] Z. Wu, B. Xu, K. Hayashi, and A. Machida, “Distributed
Journal of Intelligent Material Systems and Structures, vol. 10,
optic fiber sensing for a full-scale PC girder strengthened with
no. 4, pp. 330–339, 2000.
prestressed PBO sheets,” Engineering Structures, vol. 28, no. 7,
pp. 1049–1059, 2006. [29] J. P. Newhook, B. Bakht, A. Mufti, and G. Tadros, “Monitoring
[15] R. M. Measures, A. T. Alavie, R. Maaskant, M. Ohn, S. Karr, of Hall’s harbour wharf,” in Health Monitoring and
and S. Huang, “A structurally integrated Bragg grating laser Management of Civil Infrastructure Systems, vol. 4337 of
sensing system for a carbon fiber prestressed concrete highway Proceedings of SPIE, pp. 234–244, March 2001.
bridge,” Smart Materials and Structures, vol. 4, no. 1, pp. 20– [30] P. L. Fuhr, D. R. Huston, P. J. Kajenski, and T. P. Ambrose,
30, 1995. “Performance and health monitoring of the Stafford Medical
[16] R. C. Tennyson, A. A. Mufti, S. Rizkalla, G. Tadros, and Building using embedded sensors,” Smart Materials and
B. Benmokrane, “Structural health monitoring of innovative Structures, vol. 1, no. 1, pp. 63–68, 1992.
bridges in Canada with fiber optic sensors,” Smart Materials [31] I. B. Kwon, C. Y. Kim, and M. Y. Choi, “Continuous
and Structures, vol. 10, no. 3, pp. 560–573, 2001. measurement of temperature distributed on a building
[17] B. Benmokrane, H. Rahman, P. Mukhopadhyaya et al., “Use construction,” in Smart Structures and Materials: Smart
of fibre reinforced polymer reinforcement integrated with Systems for Bridges, Structures, and Highways, vol. 4696 of
fibre optic sensors for concrete bridge deck slab construction,” Proceedings of SPIE, pp. 273–283, March 2002.
Canadian Journal of Civil Engineering, vol. 27, no. 5, pp. 928– [32] P. Rossi and F. Le Maou, “New method for detecting cracks in
940, 2000. concrete using fibre optics,” Materials and Structures, vol. 22,
[18] A. A. Mufti, G. Tadros, and P. R. Jones, “Field assessment of no. 6, pp. 437–442, 1989.
fibre-optic Bragg grating strain sensors in the confederation [33] C. K. Y. Leung, N. Elvin, N. Olson, T. F. Morse, and Y.-F.
bridge,” Canadian Journal of Civil Engineering, vol. 24, no. 6, He, “A novel distributed optical crack sensor for concrete
pp. 963–966, 1997. structures,” Engineering Fracture Mechanics, vol. 65, no. 2-3,
[19] R. Brönnimann, PH. M. Nellen, and U. Sennhauser, “Reli- pp. 133–148, 2000.
ability monitoring of CFRP structural elements in bridges [34] K. T. Wan and C. K. Y. Leung, “Applications of a distributed
with fiber optic Bragg grating sensors,” Journal of Intelligent fiber optic crack sensor for concrete structures,” Sensors and
Material Systems and Structures, vol. 10, no. 4, pp. 322–329, Actuators A, vol. 135, no. 2, pp. 458–464, 2007.
2000. [35] N. Elvin, C. K. Y. Leung, V. S. Sudarshanam, and S. Ezekiel,
[20] D. Inaudi and S. Vurpillot, “Monitoring of concrete bridges “Novel fiber optic delamination detection scheme: theoretical
with long-gage fiber optic sensors,” Journal of Intelligent and experimental feasibility studies,” Journal of Intelligent
Material Systems and Structures, vol. 10, no. 4, pp. 280–292, Material Systems and Structures, vol. 10, no. 4, pp. 314–321,
2000. 2000.
12 Advances in Civil Engineering

[36] X. Gu, Z. Chen, and F. Ansari, “Method and theory for a [53] G. Park, K. Kabeya, H. H. Cudney, and D. J. Inman,
multi-gauge distributed fiber optic crack sensor,” Journal of “Impedance-based structural health monitoring for
Intelligent Material Systems and Structures, vol. 10, no. 4, pp. temperature varying applications,” JSME International
266–273, 2000. Journal, Series A, vol. 42, no. 2, pp. 249–258, 1999.
[37] X. Chen and F. Ansari, “Fiber optic stress wave sensor for [54] Y. Yang, Y. Y. Lim, and C. K. Soh, “Practical issues related to
detection of internal flaws in concrete structures,” Journal of the application of the electromechanical impedance technique
Intelligent Material Systems and Structures, vol. 10, no. 4, pp. in the structural health monitoring of civil structures. I.
274–279, 2000. Experiment,” Smart Materials and Structures, vol. 17, no. 3,
[38] Z. Chen and A. Farhad, “Embedded fiber optic sensors for Article ID 035008, p. 14, 2008.
detection of acoustic emissions in structures,” Acta Optica [55] Y. Yang, Y. Y. Lim, and C. K. Soh, “Practical issues related to
Sinica, vol. 20, no. 8, pp. 1060–1064, 2000. the application of the electromechanical impedance technique
[39] D. C. Betz, G. Thursby, B. Culshaw, and W. J. Staszewski, in the structural health monitoring of civil structures. II.
“Acousto-ultrasonic sensing using fiber Bragg gratings,” Smart Numerical verification,” Smart Materials and Structures, vol.
Materials and Structures, vol. 12, no. 1, pp. 122–128, 2003. 17, no. 3, Article ID 035008, p. 12, 2008.
[40] N. R. Swamy and R. M. Wan, “Use of dynamic nondestructive
[56] C. K. Soh, K. K.-H. Tseng, S. Bhalla, and A. Gupta,
test methods to monitor concrete deterioration due to alkali-
“Performance of smart piezoceramic patches in health
silica reaction,” Cement, Concrete and Aggregates, vol. 15, no.
monitoring of a RC bridge,” Smart Materials and Structures,
1, pp. 32–49, 1993.
vol. 9, no. 4, pp. 533–542, 2000.
[41] M. Sansalone, J.-M. Lin, and W. B. Streett, “Determining the
depth of surface-opening cracks using impact-generated stress [57] K. K. Tseng and L. Wang, “Smart piezoelectric transducers for
waves and time-of-flight techniques,” ACI Materials Journal, in situ health monitoring of concrete,” Smart Materials and
vol. 95, no. 2, pp. 168–177, 1998. Structures, vol. 13, no. 5, pp. 1017–1024, 2004.
[42] Y.-C. Jung, T. Kundu, and M. R. Ehsani, “A new nondestructive [58] Y. Y. Lim, S. Bhalla, and C. K. Soh, “Structural identification
inspection technique for reinforced concrete beams,” ACI and damage diagnosis using self-sensing piezo-impedance
Materials Journal, vol. 99, no. 3, pp. 292–299, 2002. transducers,” Smart Materials and Structures, vol. 15, no. 4,
[43] P. L. Fuhr and D. R. Huston, “Corrosion detection in pp. 987–995, 2006.
reinforced concrete roadways and bridges via embedded fiber [59] Y. Wen, Y. Chen, P. Li, D. Jiang, and H. Guo, “Smart concrete
optic sensors,” Smart Materials and Structures, vol. 7, no. 2, with embedded piezoelectric devices: implementation and
pp. 217–228, 1998. characterization,” Journal of Intelligent Material Systems and
[44] R. C. Tennyson, T. Coroy, G. Duck et al., “Fibre optic sensors Structures, vol. 18, no. 3, pp. 265–274, 2007.
in civil engineering structures,” Canadian Journal of Civil [60] C. S. Wang, F. Wu, and F.-K. Chang, “Structural health
Engineering, vol. 27, no. 5, pp. 880–889, 2000. monitoring from fiber-reinforced composites to steel-
[45] Y. Wang, D.-K. Liang, and B. Zhou, “Measurement of steel reinforced concrete,” Smart Materials and Structures, vol. 10,
corrosion in concrete structures by analyzing long-period no. 3, pp. 548–552, 2001.
fiber grating spectrum character,” Spectroscopy and Spectral [61] F. Wu and F.-K. Chang, “A built-in active sensing diagnostic
Analysis, vol. 28, no. 11, pp. 2660–2664, 2008 (Chinese). system for civil infrastructure systems,” in Smart Systems
[46] P. Cosentino, B. Grossman, C. Shieh, S. Doi, H. Xi, and P. for Bridges, Structures, and Highways-Smart Structures and
Erbland, “Fiber-optic chloride sensor development,” Journal Materials, vol. 4330 of Proceedings of SPIE, pp. 27–35,
of Geotechnical Engineering, vol. 121, no. 8, pp. 610–617, 1995. March 2001.
[47] W. C. Michie, B. Culshaw, M. Konstantaki et al., “Distributed [62] F. Wu and F. K. Chang, “Diagnosis of debonding in steel-
pH and water detection using fiber-optic sensors and reinforced concrete with embedded piezoelectric elements,”
hydrogels,” Journal of Lightwave Technology, vol. 13, no. 7, pp. in Proceedings of the 3rd International Workshop on Structural
1415–1420, 1995. Health Monitoring: The Demands and Challenges, F. K. Chang,
[48] W. Grahn, P. Makedonski, J. Wichern, W. Kowalsky, and Ed., pp. 670–679, CRC Press, New York, NY, USA, 2001.
S. Wiese, “Fiberoptical sensors for in-situ monitoring of
[63] G. Kawiecki, “Feasibility of applying distributed piezotrans-
moisture and pH-value in reinforced concrete,” in Imaging
ducers to structural damage detection,” Journal of Intelligent
Spectrometry VII, vol. 4480 of Proceedings of SPIE, pp.
Material Systems and Structures, vol. 9, no. 3, pp. 189–197,
395–403, August 2001.
1998.
[49] C. Liang, F. P. Sun, and C. A. Rogers, “Coupled electro-
mechanical analysis of adaptive material systems— [64] M. Saafi and T. Sayyah, “Health monitoring of concrete
determination of the actuator power consumption and structures strengthened with advanced composite materials
system energy transfer,” Journal of Intelligent Material Systems using piezoelectric transducers,” Composites Part B, vol. 32,
and Structures, vol. 5, no. 1, pp. 12–20, 1994. no. 4, pp. 333–342, 2001.
[50] J. W. Ayres, F. Lalande, Z. Chaudhry, and C. A. Rogers, [65] M. Q. Sun, W. J. Staszewski, R. N. Swamy, and Z. Q. Li,
“Qualitative impedance-based health monitoring of civil “Application of low-profile piezoceramic transducers for
infrastructures,” Smart Materials and Structures, vol. 7, no. 5, health monitoring of concrete structures,” NDT and E
pp. 599–605, 1998. International, vol. 41, no. 8, pp. 589–595, 2008.
[51] S. Park, C.-B. Yun, Y. Roh, and J.-J. Lee, “PZT-based active [66] G. B. Song, H. C. Gu, and Y.-L. Mo, “Smart aggregates:
damage detection techniques for steel bridge components,” multi-functional sensors for concrete structures—a tutorial
Smart Materials and Structures, vol. 15, no. 4, pp. 957–966, and a review,” Smart Materials and Structures, vol. 17, no. 3,
2006. Article ID 033001, 2008.
[52] G. Park, H. H. Cudney, and D. J. Inman, “Impedance-based [67] Z. Li, D. Zhang, and K. Wu, “Cement-based 0–3 piezoelectric
health monitoring of civil structural components,” Journal of composites,” Journal of the American Ceramic Society, vol. 85,
Infrastructure Systems, vol. 6, no. 4, pp. 153–160, 2000. no. 2, pp. 305–313, 2002.
Advances in Civil Engineering 13

[68] Y. Y. Lu and Z. J. Li, “Cement-based piezoelectric sensor magnetostrictive sensor technology,” in Proceedings of the 3rd
for acoustic emission detection in concrete structures,” International Workshop on Structural Health Monitoring: The
in Proceedings of the 11th Aerospace Division International Demands and Challenges, F.-K. Chung, Ed., pp. 384–392, CRC
Conference on Engineering, Science, Construction, and Opera- Press, New York, NY, USA, 2001.
tions in Challenging Environments, vol. 323, March 2008. [85] W.-B. Na and T. Kundu, “EMAT-based inspection of concrete-
[69] X. Y. Zhao, H. N. Li, D. Du, and J. L. Wang, “Concrete filled steel pipes for internal voids and inclusions,” Journal of
structure monitoring based on built-in piezoelectric ceramic Pressure Vessel Technology, vol. 124, no. 3, pp. 265–272, 2002.
transducers,” in Sensors and Smart Structures Technologies [86] W.-B. Na and T. Kundu, “A combination of PZT and EMAT
for Civil, Mechanical, and Aerospace Systems, vol. 6932 of transducers for interface inspection,” Journal of the Acoustical
Proceedings of SPIE, p. 8, March 2008. Society of America, vol. 111, no. 5 I, pp. 2128–2139, 2002.
[70] P.-W. Chen and D. D. L. Chung, “Carbon fiber reinforced [87] P. Bouchilloux, N. Lhermet, and F. Claeyssen,
concrete for smart structures capable of non-destructive flaw “Electromagnetic stress sensor for bridge cables and
detection,” Smart Materials and Structures, vol. 2, no. 1, pp. prestressed concrete structures,” Journal of Intelligent Material
22–30, 1993. Systems and Structures, vol. 10, no. 5, pp. 397–401, 2000.
[71] P. Chen and D. D. L. Chung, “Carbon-fiber-reinforced [88] P. Rizzo and F. L. Di Scalea, “Wavelet-based feature extraction
concrete as an intrinsically smart concrete for damage for automatic defect classification in strands by ultrasonic
assessment during dynamic loading,” Journal of the American structural monitoring,” Smart Structures and Systems, vol. 2,
Ceramic Society, vol. 78, no. 3, pp. 816–818, 1995. no. 3, pp. 253–274, 2006.
[72] D. D. L. Chung, “Self-monitoring structural materials,” Mate-
rials Science and Engineering, vol. 22, no. 2, pp. 57–78, 1998.
[73] Q. Mao, B. Zhao, D. Sheng, and Z. Li, “Resistance changement
of compression sensible cement speciment under different
stresses,” Journal Wuhan University of Technology, vol. 11, no.
3, pp. 41–45, 1996.
[74] M. Sun, Z. Li, Q. Mao, and D. Shen, “A study on thermal
self-monitoring of carbon fiber reinforced concrete,” Cement
and Concrete Research, vol. 9, no. 5, pp. 769–771, 1999.
[75] S. Wen and D. D. L. Chung, “Carbon fiber-reinforced cement
as a strain-sensing coating,” Cement and Concrete Research,
vol. 31, no. 4, pp. 665–667, 2001.
[76] W. Wang, H. Dai, and S. Wu, “Mechanical behavior and
electrical property of CFRC-strengthened RC beams under
fatigue and monotonic loading,” Materials Science and
Engineering A, vol. 479, no. 1-2, pp. 191–196, 2008.
[77] X. Wang and D. D. L. Chung, “Short carbon fiber reinforced
epoxy coating as a piezoresistive strain sensor for cement mor-
tar,” Sensors and Actuators, A, vol. 71, no. 3, pp. 208–212, 1998.
[78] N. Muto, H. Yangagida, T. Nakatsuji et al., “Self-diagnosing
performance for fracture in CFGRP-reinforced concrete,”
Journal of the Ceramic Society of Japan, vol. 101, no. 1176, pp.
860–866, 1993.
[79] M. Sugita, H. Yanagida, and N. Muto, “Materials design for
self-diagnosis of fracture in CFGFRP composite reinforce-
ment,” Smart Materials and Structures, vol. 4, no. 1A, pp.
52–57, 1995.
[80] N. Muto, Y. Arai, S. G. Shin et al., “Hybrid composites
with self-diagnosing function for preventing fatal fracture,”
Composites Science and Technology, vol. 61, no. 6, pp. 875–883,
2001.
[81] C. Q. Yang and Z. S. Wu, “Self-structural health monitoring
function of RC structures with HCFRP sensors,” Journal of
Intelligent Material Systems and Structures, vol. 17, no. 10, pp.
895–906, 2006.
[82] C. Yang, Z. Wu, and Y. Zhang, “Structural health monitoring
of an existing PC box girder bridge with distributed HCFRP
sensors in a destructive test,” Smart Materials and Structures,
vol. 17, no. 3, Article ID 035032, p. 10, 2008.
[83] H. Kwun and K. A. Bartels, “Magnetostrictive sensor
technology and its applications,” Ultrasonics, vol. 36, no. 1–5,
pp. 171–178, 1998.
[84] D. A. Khazem, H. Kwun, S. Y. Kim, and C. Dynes, “Long-range
inspection of suspender ropes in suspension bridges using the