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Introduction
to Seismic
Rehabilitation
Process
Seismic
risk
evaluation
and
seismic
upgrading
is a
complex
and often
intimidating
task.
Planning
for a risk
that can
come at
any time,
but
happens
infrequently
is
difficult.
Earthquakes
are unique
in natural
disasters
in that
they can
occur
without
warning,
and thus
can place
people at
risk in
vulnerable
structures
who in
other
natural
hazards
would be
able to
retreat to
a safe
location.
This
places an
extra
burden on
building
owners,
and on
local
government,
to ensure
that
occupants
and other
users of
facilities
are not
unduly
exposed.
Thus, the
principle
purpose of
hazard
mitigation
is the
protection
of life,
even when
the risk
to a
single
individual
at any one
time is
comparatively
small.
To gain
an
understanding
of the
"seismic
rehabilitation
process,"
it is best
to
subdivide
the
endeavor
into a
series of
steps, and
identify
the
disciplines
required
for each
step -
from that
of the
building
ownership
and
management,
to that of
the
architect
and
structural
engineer.
The
seismic
rehabilitation
process is
not
entirely
concentrated
in the
discipline
of
structural
engineering.
It calls
on the
disciplines
of
Seismology,
Public
Administration,
Risk
Analysis,
Statistics,
Economics,
Building
Conservation
Technology,
and
Materials
Testing
and
Inspection,
to name
just a
few.
The
decision
for an
owner may
have to do
with an
evaluation
of the
risk and
economic
viability
of an
asset.
However,
for a
whole
community,
it is
difficult
decisions
over where
to place
public
investment
when
limited
resources
are
available.
One of
the most
important
things to
consider
is that
what may
seem
obvious at
first
glance may
become
less
obvious on
more
detailed
examination.
Buildings
that,
because of
their age
and the
nature of
their
structural
system,
may have
been
identified
in overall
surveys as
hazardous
(say,
because
they are
constructed
of
unreinforced
masonry,)
may on
closer
inspection,
be found
to be
comparatively
less risky
than
nearby
newer
structures
of
non-ductile
concrete
frame.
These
newer
buildings
may be
used by
many more
people in
any given
day, and
thus
placing a
far
greater
risk on
the
community
than the
older
masonry
building.
If this is
found to
be the
case, then
which do
you
upgrade?
A prudent
administrator
in such a
situation
may find
that the
route to
take is to
fix the
one which
combines
high
occupancy
with
collapse
potential
instead of
the one
with lower
occupancy
which
none-the-less
may also
be easily
damaged,
but may
not be
likely to
collapse.
Another
factor may
be the
need to
upgrade
facilities
that are
critically
important
use in a
post-earthquake
environment,
such as
fire
stations
and
hospitals.
All such
factors
must be
weighed
when
making the
kinds of
decisions
that
require
the
investment
of
comparatively
large sums
of money
to carry
out tasks
whose
value will
only
become
apparent
when and
if an
earthquake
indeed
does
happen.
It is
also
important
to
understand
one of the
lesser
known
facts
about the
structural
engineering
design
process
that can
have a
significant
impact on
the costs,
whether
they be
with
public
funds or
private
investment.
In many
cases
involving
the larger
more
complex
structures,
it has
proven to
be the
case that
any funds
beyond the
minimum
that is
invested
in
engineering
analysis
up front,
may have a
large
payoff in
the end in
terms of
money
saved on
construction
costs.
There are
even
examples
of
projects
that cost
one fifth
or less of
the
originally
estimated
costs as a
result of
in depth
engineering
analysis
leading to
a more
creative
design
solution.
The codes
often
prescribe
a set
procedure,
but these
same codes
allow
other more
time
consuming
and
sophisticated
analysis
techniques
to be used
in lieu of
that
procedure.
It is
important
for the
decision
makers to
understand
that the
difference
does not
mean that
such a
design
would fail
to meet
code, but
that the
standard
code
procedures
tend to be
over
conservative
by
comparison
because,
absent the
more
detailed
analysis,
one would
have no
scientifically
derived
basis for
the design
decisions
that are
specific
to the
subject
building.
In
light of
this, the
decision
maker on a
given
project is
on the
horns of a
dilemma.
He or she
must
decide if
the
further
investment
in
engineering
analysis
will bear
fruit
before it
can be
known that
it
will.
This
decision
comes at a
time when
access to
funding
for the
project
may be
extremely
difficult.
Once
construction
is
underway,
the
funding
sources
are, of
course,
already
identified,
and the
schedule
set, but
getting
funds in
place at
the design
stage can
be more
difficult.
The point
is made
only to
emphasize
the
importance
of careful
and
complete
analysis
in the
Seismic
Rehabilitation
Process if
scarce
resources
are to be
husbanded
for the
most cost
effective
results,
either on
an
individual
project,
or for a
whole
district
of
community.
Seismic
Review
Process
Steps
The
Seismic
Rehabilitation
process
can be
subdivided
into a
series of
steps.
The first
step is to
determine
the
rehabilitation
objective.
In order
to do
this, the
subject
building(s)
need to be
evaluated
not only
in terms
of
engineering,
but also
in terms
of the
societal
issues,
from which
one can
determine
the value
of the
rehabilitated
structure
in both
monetary
and
non-monetary
terms.
Considerations
such as
whether or
not the
building
is
historic,
is
architecturally
significant
(which can
be
affected
by the
rehabilitation
design),
is used by
many
people all
the time,
or for a
short
period of
time (such
as a
church on
Sundays,
which is
empty
during the
week),
etc.
This
evaluation
also must
cover the
technical
issues -
both the
safety of
the
structure
and the
safety of
the
building's
non-structural
features
and
contents.
Following
the
evaluation
of all of
these
elements,
a
"Rehabilitation
Objective"
can be
defined.
This
Rehabilitation
Objective
is an
expectation
of the
performance
of a
building
after a
seismic
event of a
particular
magnitude.
Building
performance
can be
described
qualitatively
in terms
of the
safety
afforded
building
occupants
during and
after the
event; the
cost and
feasibility
of
restoring
the
building
to
pre-earthquake
condition;
the length
of time
the
building
is removed
from
service to
effect
repairs;
and
economic,
architectural,
or
historic
impacts on
the larger
community.
These
performance
characteristics
are
directly
related to
the extent
of damage
that would
be
sustained
by the
building.
A
more
detailed
discussion
of the
determination
of a
Rehabilitation
Objective
can be
found in FEMA
356.
In
summary,
the
objective
can be to
achieve a
performance
level
after
rehabilitation
that lies
somewhere
on a
continuum
from
"Collapse
Prevention,"
through
"Life
Safety"
and
"Damage
Control"
to
"Immediate
Occupancy."
Above that
- reserved
for the
most
critical
or
hazardous
facilities,
would be
"Operational"
level.
For almost
all
buildings
in
ordinary
public and
private
use, a
performance
level that
presumes
no damage
is
economically
impractical,
and not
necessary
to meet
public
responsibilities
and
balance
the risks
of damage
with the
costs of
construction
or
upgrading.
In
reference
to this,
it is
important
to
understand
that the
current
codes for
new
construction
are based
on an
acceptance
of damage
from
earthquake
forces in
a moderate
to large
earthquake.
In a large
earthquake,
that
damage
could be
extensive.
The code
objective
is to
prevent
collapse
and
minimize
falling
debris,
not to
prevent
damage.
On the
issue of
codes, it
is also
important
to
understand
that most
local
codes are
written to
deal with
new
construction.
As such,
their
provisions
may not be
appropriate
for the
seismic
rehabilitation
of
existing
buildings.
Existing
buildings,
particularly
those
constructed
using
technologies
and
construction
methods
which have
since gone
out of
use, are
not
suitable
for
redesign
following
the
detailed
proscriptive
provisions
of new
building
codes.
This does
not mean
that they
cannot be
made to
meet the
objectives
of the
current
code in
terms of
safety and
performance
as
described
in the
previous
paragraph,
only that
they
cannot be
assumed to
be able to
do it in
the same
way as is
done for
new
construction.
In recent
years,
there have
been a
number of
important
codes, and
guidance
documents
prepared
specifically
to aid in
the
rehabilitation
and
seismic
upgrading
of
existing
buildings
of
different
types,
including those
prepared
and
published
by FEMA
used as
sources
for this
Handbook.
In
California,
and other
states,
the Uniform
Code for
Building
Conservation
has been
incorporated
into the
state's
model
code.
All of
these
sources
are likely
to be more
appropriate
for
rehabilitation
design
than are
the
standard
codes for
new
construction.
This
Handbook
The
balance of
this
section on
buildings
in this
Handbook
is divided
into three
parts: (1)
an
introduction
to
structural
concepts,
intended
to help
the
non-structural
engineer
understand
how the
structural
engineering
design
process
can impact
a project
overall,
(2) the
assessment
step, in
which a
facility
is
evaluated
according
to a
series of
major
seismic
risk
variables,
and (3) a
brief
description
of
different
seismic
upgrade
solutions.
These are
divided
into
categories
under the
different
structural
types that
are likely
to be
encountered
in most
projects.
These
illustrated
solutions
are not
intended
to be
comprehensive
or
detailed,
but rather
to provide
a simple
identification
of the
most basic
different
solutions
that are
often
carried
out for
the
representative
structural
deficiencies.
This
handbook
has
condensed
and
excerpted
materials
from the FEMA
publications
listed
above,
as well as
other
sources.
It is
intended
to provide
a basic
introduction
to what is
involved
in making
a decision
to
undertake
seismic
upgrading
of
buildings
of
differing
structural
types and
sizes.
The
following
section
provides a
description
of the
different
technical
items to
consider
in
evaluating
different
facilities,
and then
provides a
Microsoft
Excel
Spreadsheet
that can
be used to
develop a
comparative
assessment
based on
the
"Rapid
Visual
Screening"
methodology
developed
by FEMA,
and
published
in FEMA
154.
This was
first
published
in 1988,
and has
recently
been
modified
and
updated,
and is
currently
in-press.
The
numbers
used in
this
spreadsheet
are the
ones from
the
updated
2002
version.
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