II. How Could System
Identification Be Applied to Earthquake
Engineering?
damage detection. For earthquake engineering
in general, system identification, which is based on
real-world dynamic data
measurements, facilitates structural modeling for earthquake
simulation,
analysis
and design. Apart from this, many analytic and numerical tools in
system
identification that are
powerful in data processing and data interpretation are
invaluable to the earthquake engineering
community.
techniques in system identification to
earthquake engineering may be summarized in the following aspects:
2.
Introducing nonlinearities
into structural modeling;
3.
Applying probabilistic
methods for performance-based design and seismic risk assessment;
4.
Analyzing and simulating
earthquake responses;
5.
Monitoring structural
health for seismic protection, and
1. In
system identification, models are derived from real-world dynamic
measurements.
Thus the models are supposed to reflect the real status of
structures rather than being derived from
assumed and/or idealized values of
the key parameters. Although tremendous challenges exist in
correctly modeling structures based on input-output data sets, for
existing structures especially
those
aging infrastructures, being able to capture the current properties of
the structures is critical in predicting
their earthquake performance and
survivability.
2.
Nonlinearities are considered in some system identification
techniques.
Under a strong ground shaking caused by an earthquake, it is
possible for a structure to behave
in an inelastic and nonlinear range. Powerful
tools in handling linear vibrations, such as Fourier transform
and modal
analysis are normally not applicable to nonlinear problems. The need of
evaluating and
considering inelastic seismic analysis procedures has been
pointed out by the ACT-55
report
(which can be downloaded from the Applied
Technology Council website).
System identification
offers tools to model and analyze nonlinearities for the
applications in earthquake engineering. See details.
3.
Probabilistic methods are applied widely in system identification
techniques.
Probabilistic
methods play an important role in
earthquake engineering due to the random nature of
earthquake excitations and the
uncertainties involved in structural systems due to construction
errors,
material aging, and environmental changes. Similarly, probabilistic
methods are
widely studied in
system identification to deal with the complexities of the
real-world uncertainties in systems and loads.
The applications of
probabilistic methods in earthquake engineering include running
generating artificial ground motions, producing fragility curves, and
performing earthquake risk assessment.
See details.
4. Models
can be used to simulate global earthquake response of a
structure for a given/specified
earthquake ground motion.
are collected, system identification provides mathematical models
of structures. Earthquake simulation
thus becomes a forward problem utilizing a
specified ground motion time history and the model of
the structure obtained
from system identification.
5. Paired
with sensor technology, system identification can provide an
efficient means in monitoring
structural health for seismic protection. See details.
6. Various
numerical schemes and signal processing methods developed or
applied in system identification
are highly relevant to earthquake engineering
applications. Earthquake excitations and responses can be
simulated numerically
or measured from a laboratory setting or from site. It can become a
routine to
handle
long data sets in earthquake engineering. System identification
provides
various powerful tools in
data processing and data interpretation. Apart from the
widely applied modal analysis based approaches,
there are various techniques
handling nonlinear systems and non-stationary data measurements
associated
with
strong earthquake motions. Among them, there are artificial
neural networks,
wavelets, and
Hilbert
Huang transform. The last one is an emerging technique, and
the first two are considered as
black-box methods. Clicks the links for details.