Civil Engineering Reference
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deployment, customized wireless sensor nodes with dedicated communication
software have been designed. The WSN-based SHM system installed in the tower
consists of 16 sensor nodes, among them are two fiber-optic strain gauges, three
accelerometers, and 11 temperature sensors. These sensor nodes, in together with
one sink node, are distributed in the five floors of the tower and constitute a multi-
hop wireless communication network. The system, which has been operating since
September 2008, can run for four months without changing batteries, which is a
good performance when compared with other WSN-based SHM systems. Also, the
data loss ratio was estimated to be less than 0.01%. However, this system only
contains 16 sensors, and the performance of the system is unclear if more sensor
nodes are included. In addition, the long lifetime of the system is at the expense of
long working interval: only three sensor nodes are equipped with accelerometers
and they only work for about six minutes every day.
11.1.5 The challenges for WSN-based SHM
In this section, the main challenges for WSN-based SHM are summarized. As
mentioned in the previous sections, energy consumption, fast and reliable data
delivery through a wireless link, and implementing energy efficient and effective
SHM algorithms are the three main challenges for a WSN-based SHM system.
Another interesting as well as challenging problem in WSN-based SHM is sensor
node deployment. Optimal sensor node deployment in WSN-based SHM should
consider concerns from both computer science engineering (e.g., connectivity,
routing, and energy consumption) and civil engineering (damage detection
capability). This problem is first considered by Li
et al
. (2010), but it assumes a
static WSN with disk communication model. More practical deployment strategy
needs to be designed to handle the dynamic nature of WSN.
The last point to mention is associated with the middleware framework for
WSN-based SHM applications. SHM application programmers, particularly civil
engineers are generally not familiar with the operating system of WSN
(i.e. TinyOS), and may not like to be exposed to the intricacies of WSNs, such
as wireless communication and energy management. Therefore, middleware
framework that is able to provide programming abstractions is quite important.
However, developing middleware framework for WSN-based SHM system is not a
trivial task. The main difficulty comes from the diversity of SHM applications. How
to design a versatile middleware framework that can be adopted for different SHM
applications is a challenging task.
In this chapter, five key challenges of WSN-based SHM are identified. They are
(1) How to realize long-term monitoring using battery-powered wireless sensor
nodes.
(2) How to design and implement simple and effective SHM algorithms.
(3) How to realize fast and reliable data delivery through the wireless link.
(4) How to deploy wireless sensor nodes in a WSN-based SHM system.
(5) How to establish a general middleware framework for various WSN-based
SHM applications.
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