Structural Health Monitoring Using Smart Sensors - ideals ...

equirements, appropriate middleware services will need to be adopted, modified, or
developed.
2.3 Structural Health Monitoring
Structural Health Monitoring (SHM) strategies measure structural response and aim
to effectively detect, locate, and assess damage produced by severe loading events and by
progressive environmental deterioration. Structural response reflects the structural
condition as well as the excitation force. By analyzing the response data, SHM strategies
are expected to reveal structural condition, such as the damage existence. SHM has seen
intense research efforts in mechanical, aerospace, and maritime, as well as civil
engineering applications. In particular, condition-based machinery maintenance utilizing
vibration monitoring has seen many applications (Al-Najjar, 2000; Collacott, 1977). Once
damage is detected, detailed Non-Destructive Testing (NDT), repair, and/or suspension of
service follow. Well-known NDT techniques include visual inspection, eddy current
testing, acoustic emission, ultrasonic testing, and radiographic inspection (Gros, 1997).
SHM leads to well-organized maintenance of structures.
Efficient and effective maintenance is among motivations to introduce SHM
strategies for various applications. The Electric Power Research Institute (EPRI) has
successfully demonstrated the use of diagnostic technology at its Eddystone Station fossilfuel
power plant outside of Philadelphia. Since the 1987 installation of a dual-purpose
vibration monitor and rotor-crack detector for bearing wear at the plant, EPRI says it has
saved $250,000 in costs for teardown of machinery. In military applications, SHM is
expected to reduce maintenance and manpower requirements by approximately 20 to 40
percent, increase combat sorties by 25 percent, and reduce the complexity of the logistics
trail by 50 percent, compared to current military strike aircraft (Becker et al., 1998). SHM
in these fields has been shown to be a practical and an attractive solution for maintenance.
From a civil engineering perspective, SHM is expected to provide an efficient and
effective tool for management of infrastructure. Civil infrastructure is a valuable asset,
which keeps the economy and people's life running. For example, a long-span bridge such
as the Akashi-Kaikyo Bridge in Japan costs billions of dollars, while the Golden Gate
Bridge in California has about 40 million crossings per year (Golden Gate Bridge,
Highway and Transportation District, 2005). These structures, however, deteriorate with
age. Many of the 1,100 major long-span bridges in the U.S. are over 50 years old and
several notable ones are over 100 years old. More than 800 of the long-span bridges in the
National Bridge Inventory are classified as fracture-critical (Pines & Aktan, 2002). The
structural integrity and serviceability of these structures are not necessarily apparent.
Because failure of such civil infrastructure can have significant negative impacts on
society at large, structures need to be managed based on the understanding of their current
structural conditions. The current practice, visual inspection, is expensive both in time and
cost. For example, the biennial visual inspection of a major bridge such as the Brooklyn
Bridge in New York is reported to last for over 3 months at a cost of $1 million (Dubin &
Yanev, 2001; Pines & Aktan, 2002); note that the reliability of such visual inspection is
17