Structural Health Monitoring Using Smart Sensors - ideals ...

Chapter 1
INTRODUCTION
1.1 Monitoring of civil infrastructure
Our lives rely heavily on the pervasive civil infrastructure in which industrialized
nations have huge investments. Malfunctioning of civil infrastructure has caused
tremendous economic loss and claimed numerous human lives. Civil infrastructure is,
thus, critical to keep our economy running, while the infrastructure itself is an important
asset to be managed.
To properly manage civil infrastructure, its condition, or serviceability, must be
assessed. Many variables can be monitored and used for the assessment. For instance,
Intelligent Transportation Systems make use of traffic surveillance information to
efficiently manage the transportation system. Tunnels are monitored for traffic accidents
and air quality. The Urgent Earthquake Detection and Alarm System (Nakamura, 2004)
detects primary seismic waves and stops trains before severe secondary waves approach.
Measurement and proper data processing are expected to give a reasonable assessment of
serviceability that can then be improved based on the assessment.
The physical state of a structural system, for example, applied load, vibration level,
and existence of structural damage, is among the factors that determine serviceability.
Sensing physical quantities in detail offers the potential to better estimate structural
conditions. For river bank protection, for instance, water level may be monitored and the
associated load estimated. Precipitation rate and groundwater level are important
indicators to predict slope failure. Strain and temperature measurements can be utilized to
monitor concrete gravity or arch dams. Engineers, owners, and users can make better
decisions based on the measured information.
Structural condition assessment is, however, not always straightforward as in the case
of the Structural Health Monitoring (SHM) of buildings, bridges, and towers. The
structural condition is oftentimes sought in terms of structural characteristics, i.e., mass,
damping, stiffness matrices, damage existence, and/or applied load to the system. These
structures are large and consist of many members, which makes such structural condition
assessment difficult and/or prohibitively expensive. One approach in SHM to alleviate this
difficulty is based on vibration measurement. Though structural characteristics and
applied load are difficult to assess directly, dynamic behavior, which is a function of the
structural characteristics and applied load, can be measured. The structural characteristics
and applied load information lurk in the dynamic behavior. Structural soundness is
expected to be estimated by inverse analyses of the dynamic behavior.
Because buildings, bridges, and towers are typically large and complex, information
from just a few sensors is inadequate to accurately assess the structural condition. The
dynamic behavior of these structures is complex in both spatial and time scale. Moreover,
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