to the HOT
TOPIC in Earthquake
Engineering # 8 !
DESIGN CODE and EARTHQUAKE
Earthquake design procedures and those of
structural evaluation for the earthquake insurance industry have been totally
incompatible. One of the main reasons for this is obvious: the insurance
industry is exclusively performance oriented while the seismic design is,
mostly, not .
The earthquake loss estimation is usually
performed in terms of a Damage Ratio,
or a ratio of the earthquake damage dollar amount to the total value of
the building. For a long time it was associated with a collection of mass
inventory data and was based, mostly, on experts' opinions. It looks, therefore,
more like an art than a science.
A considerable step forward was made lately,
with the completion of project called HAZUS
(1997) offering a fully computerized
procedure for loss estimation. However, inconsistencies in the direct
physical damage evaluation still require major improvements.
| Motion-Damage Relationships of the HAZUS
have two basic deficiencies:
1. They are
not written in the building code language and, therefore, cannot be adequately
quantified for a computerized design and analysis.
2. Those relationships
are based, at least partially, on experts' judgments valid for an average
construction. Besides, they are most applicable for a statistically large
number of facilities.
| On the contrary, a
Damage Ratio Charts Method or DRCM is
based on a consistent quantitative analysis targeting a prediction of the
damage ratios and employs a limited number of well-understood structural
and earthquake related parameters (Shustov, 1997).
It establishes a direct theoretical relationship between the standard structural
design procedure and the expected damage characteristics required by insurers.
The method is easy and user-friendly: its application, supported by a site-specific
evaluation, will not take more than a few days.
| System of sampling buildings per DRCM
is based on the following quantitative characteristics:
Factor Rw of
the building structural system, which is understood, irrespective of any
reevaluations, as a degree the system can be allowed to go to beyond the
of stories N.
Lateral Stiffness Ke/m
of the ground story where Ke
is the aggregate lateral stiffness of the story and m is its lumped mass.
value corresponds to the elastic range of horizontal deformations of the
vertical or horizontal load carrying elements, whichever is less.
Performance Rating R (Shustov,
1994) may be used as a fundamental criterion:
R = v/ve where v is an actual or
calculated inter-story drift and ve is
a drift at the assumed elastic limit of deformation (Topic
7). The ultimate allowable value of R will occur
when R = Rw = vu/ve
where Quality Factor Rw
understood as the ratio of the ultimate allowable story drift
that can be tolerated by the structure without a collapse to the maximum
elastic story drift ve.
Ratio R / Rw
called a Seismic Performance Ratio
the anticipated losses due to a seismic exposure. It is not the sole possible
measure of seismic performance. However, in a majority of cases it is the
most important one which would determine the Damage
| How to relate physical damage to economic losses
may constitute a separate topic. Meantime, as the first degree of approximation,
the following formula may apply: D.R. = 0.3(R/Rw)3100
%. The formula is represented graphically above and it demonstrates that
when R/Rw (the current building
standards' moment of truth: Demand
equals Ultimate Capacity), D.R.
= 30 %. When R value reaches 1.5 Rw,
the building's losses approach its replacement value.
Ratio Charts (DRC) is a graphical
environment that introduces a new, streamlined way of organizing a valuable
information on the anticipated performance of buildings. DRC
contours connect the points of the equal D.R. in the domain of Rw
R/Rw depends upon the type of structure,
number of stories, and earthquake intensity. Due to this, a system of DRC
is needed to account for a wide variety of design configurations.
| Such system constitutes a matrix called a
An element of the matrix, or a
a family of damage ratio isograms.
Unlike HAZUS 97, the DRCS
introduces all variety of different building types with the help of the
single parameter Rw
| Implementation of Damage Ratio
Charts Systems will decrease a need in lengthy preliminary computations
and will make unnecessary some costly services of risk management engineers.
| Shustov, V.,
1994, "Energy Absorbing Technique: Challenge of Proportioning", Proc. 3rd
Conf. on Structures under Shock and Impact, Madrid, Spain.
HAZUS 97, 1997, Loss Estimation
Product Package, developed by RMS under contract to
NIBS funded by FEMA, Washington, DC.
Shustov, V., 1997, "Future
Seismic Codes and Earthquake Insurance", Proc. 66th Annual
SEAOC Convention, San Diego, CA.
This page was last updated on
30 March 2000