Recent years have been characterized by the unveiling of
instrumental data under strongmotion earthquake
recordings. The empirical studies that were conducted
involved parameters like the peak ground acceleration.
The use of the peak ground acceleration produces poor
results in the estimation of losses because of lack of a
correlation to losses experienced in the structures as a
result of damage from the earthquake. The best measure
of losses in empirical studies is based on the intensities
linked to ground motion. In cases where the seismic
hazard is defined based on intensity, the form in which
building vulnerability is represented in for most cases is
the Damage Probability Matrix. This form is used to
indicate the discrete probabilities experienced with
certain classes of structures with respect to vulnerability
and proneness to suffer damage of a particular grade [5].
The indication is for a certain intensity. The available
scales are the Modified Mercalli Intensity Scale, the
Medvedev-Sponheuer-Karnik scale, the European
Macroseismic Scale and the Parameterless Scale of
Seismic Intensity [6]. The damage probability matrix
scales are provided to reflect levels such as lower and
upper bound estimations. Intensity scales employ
qualitative terminologies like few, many and most in
estimating the number of buildings within a particular
class that have suffered a damage grade [7]. The
qualitative nature of the terms makes them become
subjective which means that they are hard to translate
into a numerical value. Their definition spans across
three ranges of percentages. When the damage
probabilities and inventory data are combined, it
becomes possible to estimate upper and lower-bound
values of the damage expected. The damage grades have
connections to the objective ratios. The ratios are
obtained from the cost incurred in repair to the cost
incurred in replacement.
The Analytic Approach
The analytic method taken to assess the damage as a
result of earthquakes is done purely from theory. Its
approach has no observational basis on which to rely
with evidence [2]. It is a theoretical simulation such as
prediction of the damage on the structure because of
earthquake loading. The vulnerability of a building is
expressed using the capacity graph which is used to
represent how a structure behavior in a non-linear
manner when there is lateral displacement [3]. One
needs a non-linear structural analysis procedure like
pseudo-static analysis otherwise known as pushover in
identifying the capacity curve. The capacity curve is a
relationship obtained indicating the variation between
the shear force at the base and the lateral movement of
the structure’s control node. The postulation is for a
reliable model for a structure of a building being
considered where the pushover analysis is applicable.
The reliable structural model can be established using
finite elements.
The other component to consider is the seismic ground
motion represented using the response spectrum under
various physical parameters such as acceleration and
displacement. The ability to correlate the response
spectrum and the capacity of a building, it is necessary to
convert the parameters from their Sa-T or conventional
domain into a domain understood through the capacity
curve like the spectral acceleration – spectral
displacement (Sa-Sd)
When contrasted with empirical studies which represent
ground motion using one parameter like the shaking
intensity, a response spectrum makes it possible to
consider the spectral content due to ground movements
[7]. The earthquake demand can be mimicked based on
the procedure selected for correlating seismic demand
with the capacity of a building or based on the response
spectra used in its random shape. Predicting the damage
a structure experiences or produces using analytical
methods while considering the capacity of a building
under a seismic experience requires various approaches.
The methods in question are the Capacity Spectrum
method, Collapse-Based Methods, Displacement-Based
Methods, and Displacement Coefficient Methods and the
Incremental Dynamic Analysis.
The attention received by CSM and DCM is of a great
kind because of the publishing of some provisions made
by FEMA. The other is CSM because such a procedure
gave a reason to have the HAZUS method. The
procedures that have been obtained from the philosophy
that advocates for Performance-Based Seismic Design
while understanding that damages on a structure is
determined using the lateral displacement method.
REFERENCES
