Recently a challenging project has been carried out for construction of a national network for safety management and
monitoring of civil infrastructures in Korea. As a part of the project, structural health monitoring (SHM) systems have
been established on railroad bridges employing various types of sensors such as accelerometers, optical fiber sensors,
and piezoelectric sensors. This paper presents the current status of railroad bridge health monitoring testbeds. Emerging
sensors and monitoring technologies are under investigation. They are local damage detection using PZT-based electro-mechanical
impedances; vibration-based global monitoring using accelerations, FBG-based dynamic strains; and
wireless sensor data acquisition systems. The monitoring systems provide real-time measurements under train-transit and
environmental loadings, and can be remotely accessible and controllable via the web. Long-term behaviors of the
railroad bridge testbeds are investigated, and guidelines for safety management are to be established by combining
numerical analysis and signal processing of the measured data.
In recent years, guided wave based structural health monitoring (SHM) techniques have attracted much attention,
because they are not only sensitive to small defects but also capable to cover a wide range in plate and pipe like
structures. The guided waves in a structure can be generated and sensed by a variety of techniques. This study proposes a
new wireless scheme for PZT excitation and sensing where power as well as data can be transmitted via laser. A
generated waveform by modulation of a laser is wirelessly transmitted to a photodiode connected to a PZT on the
structures. Then, the photodiode converts the light into an electrical signal and excite the PZT and the structure. Then,
the reflected response signal received at the sensing PZT is re-converted into a laser, which is wirelessly transmitted
back to another photodiode located in the data acquisition unit for damage diagnosis. The feasibility of the proposed
power and data transmission scheme has been experimentally investigated in a laboratory setup. Using the proposed
technology, a PZT transducer can be attached to a structure without complex electronic components and a power supply.
Structural health monitoring (SHM) techniques based on guided waves have been of great interests to many researchers.
Among various SHM devices used for guided wave generation and sensing, lead zirconate titanate (PZT) transducers and
fiber Bragg grating (FBG) sensors have been widely used because of their light weight, non-intrusive nature and
compactness. To best take advantage of their merits, combination of PZT-based guided wave excitation and FBG-based
sensing has been attempted by a few researchers. However, the PZT-based actuation and the FBG-based sensing are
basically two independent systems in the past studies. This study proposes an integrated PZT/FBG system using a single
laser source. Since power and data delivery is based on optical fibers, it may alleviate problems associated with
conventional wire cables such as electromagnetic interference (EMI) and power/data attenuation. The experimental
procedure for the proposed system is as follows. First, a tunable laser is used as the common power source for guided
wave generation and sensing. The tunable laser beam is modulated and amplified to contain an arbitrary waveform. Then,
it is transmitted to the PZT transducer node through an optical fiber for guided wave actuation. The transmitted laser
beam is also used with the FBG sensor to measure high-speed strain changes induced by guided waves. Feasibility of the
proposed technique has been experimentally demonstrated using aluminum plates. The results show that the proposed
system could properly generate and sense the guided waves compared to the conventional methods.
Guided waves based nondestructive testing (NDT) techniques have attracted many researchers' attentions for structural
health monitoring due to their relative long sensing range. These guided waves in a structure can be generated and sensed
by a variety of techniques. This study proposes a new wireless scheme for PZT excitation and sensing, where power as
well as measured data can be transmitted via laser. First, a generated waveform modulated by a laser is wirelessly
transmitted to a photodiode connected to a PZT on the structures. Then, the photodiode converts the light into an
electrical signal and excites the PZT and the structure. The reflected response signal received at the same PZT is reconverted
into a laser, which is transmitted back to another photodiode located at the data acquisition unit for diagnosis.
The feasibility of the proposed power transmission scheme has been experimentally demonstrated at a laboratory setup.
The wireless data transmission aspect is under verification. Since there is no need for a power supply and a signal
generator at the PZT transducer node, a self-sufficient PZT transducer unit can be realized with little additional
In recent years, nondestructive testing (NDT) has gained popularity for structural health monitoring and damage
detection applications. Among the NDT methods, guided wave based NDT techniques have attracted the attention of
many researchers due to their relatively long sensing range. These guided waves can be generated in a structure and
sensed by a variety of techniques. The present study proposes a new scheme for PZT excitation and sensing based on
laser and optoelectronic technologies, where power as well as data can be transmitted via laser. This paper mainly
focuses on the excitation aspect. An arbitrary waveform is generated using a light source and transmitted to the PZT. A
photodiode connected to the PZT then converts the light into an electrical signal and excites the PZT. The technique can
be configured either for wired or wireless PZT excitations. Finally, the feasibility of the proposed power transmission
scheme has been experimentally demonstrated in a laboratory setup.
The development of smart sensors for structural health monitoring and damage detection has been advanced remarkably
in recent years. Nowadays fiber optic sensors, especially fiber Bragg grating (FBG) sensors, have attracted many
researchers' interest for their attractive features, such as multiplexing capability, durability, lightweight and
electromagnetic interference immunity. In this paper, two damage detection approaches by dynamic strain
measurements using FBG sensors are presented. They are the modal strain-flexibility and the modal strain energy
methods. An experimental study was conducted to investigate the feasibility of the methods for damage detection and
localization. It has been found that the strain-based approaches using dynamic strain measurements from FBG sensors
can successfully detect and localize multiple small damages near the sensors. However, the damage detection range of
the present short-gage FBG sensors seems rather narrow. Long-gage FBG sensors would be a possible solution.