Monitoring techniques based on fiber Bragg grating sensor have proved to exhibit meaningful benefits when compared
with the current solutions of an electric nature in recent years. In this study, several fiber Bragg grating (FBG) strain
sensors were embedded into a prestressed concrete dual-room box-girder when construction at a prefabrication workshop
to monitor strain of concrete girder during prestressing tension. All FBG sensors are alive during monitoring, which
shows the advantages of robust surviving capability and long-term on-line monitoring performance. From the monitoring
results it is found that the variances in strain at the measurement sites are small and almost is linear with time in certain
one tension process, and the strain at the measurement sites almost synchronously and linearly change with the increase
of the prestress. It is also found that the changes in strain at the measurement sites during the final tension are larger than
that during the early tension.
Piezoelectric material, such as, Lead Zirconate Titanate (PZT) can be use as sensing and/or actuating element for
structural health monitoring due to its direct and converse piezoelectric effects. In this study, several fabricated PZT
impedance transducers encapsulated by cement were embedded into a plain concrete beam to detect the surface crack
damage. By monitoring the electromechanical (EM) admittance spectra of the embedded transducers, the structural
surface crack damage was investigated. From the experimental results it is found that the shape of the electrical
admittance spectra curve of the embedded PZT transducers hardly changes before and after surface crack is of presence,
and the EM admittance spectra exhibits tiny change in amplitude with the increase of crack depth, which indicate that the
embedded PZT transducers into concrete are insensitive to surface crack damage.
Reinforced concrete (RC) structure is one of most familiar engineering structure styles in the civil engineering
community, which often suffer crack damage during their service life because of some factors such as overloading,
excessive use, and bad environmental conditions. Thus early detection of crack damage is of special concern for RC
structures. Piezoelectric materials have direct and converse piezoelectric effects and can serve as actuators or sensors. A
health monitoring method based on PZT admittance signals is addressed in this paper, which use the electromechanical
coupling property of piezoelectric materials. An experimental study on health monitoring of a RC beam is implemented
based on the PZT admittance signals. In this experiment, the electrical admittances of distributed PZT sheets are
measured when the host beams are suffering from variable loads. From the obtained PZT admittance curves one can find
that the presence of incipient crack can be captured and the cracking load of the RC beam can also generally determined.
By the experimental study it is concluded that the health monitoring technique is quite effective and sensitive for RC
structures, which indicates its favorable application foreground in civil engineering field.
The basic idea of a piezoelectric admittance (reciprocal of impedance) technique for structural health monitoring is
presented in this paper. An experimental study on damage detection of a steel frame structure is operated by the use of
the high-frequency piezoelectric admittance signals. In this experiment, three PZT active sensors are bonded to three
different components around a joint of the steel frame separately, and the looseness of bolts is identified by monitoring
the variations of piezoelectric admittance measurements. From the experimental results it is found that the PZT active
sensors hold the ability to detect structural local damage, i.e. they are insensitive to the damage in far fields.
Subsequently, two damage indexes, the covariance and the cross correlation coefficient between two real admittance data
sets are defined respectively, by which the extent of damage of the frame structure is evaluated. It is found that the cross
correlation coefficient index can correctly reflect the damage extent of the frame structure qualitatively in different
frequency ranges, but the covariance index can not.
Piezoelectric materials have direct and converse piezoelectric effects and can serve as actuators and/or sensors. A piezoelectric impedance technique for crack monitoring in concrete structures is addressed in this paper, which use the electromechanical coupling property of piezoelectric materials. The basic principle of the technique is that by measuring the electrical impedance of piezoelectric ceramic sheets (PZT) bonded to the surface of host structure, the changes in structural mechanical impedance resulted from the presence of crack damage are monitored because the electrical impedance of PZT is directly related to the mechanical impedance of host structure. The main features of the technique are that it is not based on any physical models and its high frequency characteristics. An experimental study on crack monitoring of concrete beams was implemented based on the piezoelectric impedance technique. In this experiment, the electrical admittances (inverse of electrical impedances) of PZT were measured when the host beam was suffering from cracks with variable depth. Subsequently, a damage index, the root-mean-square deviation of real admittance (RMSDR) was presented, by which the locations and extents of concrete cracks were determined. It was found experimentally that the piezoelectric impedance technique for crack monitoring in concrete beam was quite effective and sensitive, which indicated its favorable application views in civil infrastructure systems.