Healthy cities continuously grow by driving
economic development while protecting cultural heritage. Success, in
part, depends on a healthy built environment that is rooted in
contemporary urban planning, sustainability and disaster resilience. Our
job, as design professionals, is to provide a built environment that
supports all of those goals. Our designs need to be efficient,
economical, adaptive, sustainable, and disaster resilient. We are doing
well on all fronts except for the last. We need to develop, and include
in the code, provisions that will provide the buildings and lifelines
needed to support disaster resilience.
Resilient communities have a credible disaster
response plan that assures a place and ability to govern after a
disaster has struck. Their power, water, and communication networks
begin operating again shortly after a disaster and people can stay in
their homes, travel to where they need to be, and resume a fairly normal
living routine within weeks. The return to a "new" normal can then
occur within a few years. While every building should protect its
occupants from harm, a select few buildings need to remain operational
and a larger group needs to be at least usable during repair. Lifeline
systems must be restored quickly to support response and reconstruction.
San Francisco is already moving in this
direction. The San Francisco Planning and Urban Research Association
(SPUR at www.spur.org) recently published four policy papers related to
what San Francisco needs from its seismic mitigation policies. Called
the Resilient City Initiative, these papers define resiliency in a
deterministic manner based on what the city needs from its buildings and
lifelines to support response, recovery and rebuilding post-disaster.
It is a set of goals that can be applied to any community facing any
natural disaster. At the heart of the recommendations are the need for
clarity in the hazard level and the expected damage from a disaster.
Engineers have used a variety of measures to
define the size of earthquakes they design to. The first, and one held
in high regard by the media, is the Richter Magnitude. Unfortunately, it
means little to earthquake engineers and is not referenced in the code.
These days, we prefer to talk about earthquakes in terms of their
probabilities of occurrence. The favorites are the 10/50 and 2/50. That
is an earthquake that will have a 10% or 2% chance of exceedence in 50
years. In the SPUR Initiative, a combined track was taken by suggesting
that every city faced three characteristic sizes of earthquakes,
(routine, expected, and extreme), and that the design for disaster
resilience should accommodate the expected earthquake defined as the
event that could occur once in the life of the building under
consideration. Urban planners and city policy makers are more
comfortable planning for "expected" events rather than "extreme" events
in all aspects of their work. For San Francisco’s buildings, it’s an
M=7.2 on San Andreas Fault located as close to the city as possible. For
lifelines, other scenario events need to be defined.
Earthquake Professionals are rarely clear about
the level of damage that can occur to their buildings and lifeline
systems in the expected earthquakes they are designing for. While this
is a comfortable position to take because of the concern about
liability, it has led to a significant misconception on the part of the
public. Because they are generally not told that their building was only
designed to keep the people safe and may actually be seriously damaged,
they believe that their buildings are "earthquake proof". SPUR decided
to tackle that misconception head on and defined eight states of damage
that clearly state whether people are safe inside and how soon the
building can be used after the shaking stops. Table 1, taken from the
SPUR Urbanist, defines these transparent performance measures that are
key to the public’s understanding of the problem and interest in the
proposed solution. These categories of damage need to become part of the
design and construction vocabulary.
Table 1: Performance Measures that Support Disaster Resilient Cities.
Cities do not need to resist disaster without
damage. In fact, history shows that, most often, recovery can occur even
though significant damage occurs. The key to success is at the heart of
disaster resilience. SPUR defines response and recovery in three
phases, the same often used by emergency planners. Table 2 defines the
needed condition of the built environment to properly support the
recovery. In the first phase, the weeklong response and rescue period,
only the emergency response centers are needed. These buildings need to
be capable of Category A performance, Safe and Operational, and the
supporting lifelines capable of Category I performance. These are the
Occupancy Category IV buildings specified in the 2006 International
Building Code (IBC), though there is no code requirement for the
lifelines.
Table 2: Resilient performance requirements for the built Environment.
The second phase of recovery focuses on restoring
the neighborhoods within 30 to 60 days so that the workforce can be
reestablished, their communities restored, and people are able to return
to a normal life style and back to work. This is a new idea that grew
out of the Katrina experience. People need to have a place to live, send
their kids to school, do their shopping, and create community if they
are to participate in the cities economic recovery. The buildings they
depend on need to be capable of Category B performance, safe and usable
during repairs, and the lifelines that serve them capable of Category II
performance. This is a new performance level, not covered by the IBC
today, though it does look a lot like the requirements for Occupancy III
buildings. There are no such requirements for lifelines.
The third phase of recovery covers the repair and
reconstruction of the affected area. Buildings need only be safe while
they are repaired or replaced within the target period. The current IBC
requirements for Occupancy I and II buildings should meet this goal,
although the extent and cost of repair needs to be planned for if the 3
year time frame is to be achieved. Funding for the repairs is a key
consideration, as are the standards that the repair needs to follow.
Pre-event planning and insurance should be given serious consideration.
In many ways, we have the tools and procedures to
create disaster resilient cities. It will require some modification to
the current IBC, significant alignment of the lifeline systems around
common performance objectives, and strong community support for adopting
the policies needed to mitigate the deficient buildings, build new
buildings to the performance levels needed, and insist that the lifeline
systems they depend on can deliver as needed. Making such a shift to
updated codes, and generating community support for new policies, is not
possible without solid, unified support from the science and
engineering communities that support design. We as design professionals
need to take the time to understand this issue, join the conversation
about how to achieve resiliency, build it into our research programs,
convince our owners to incorporate it in their projects, and be a part
of the common voice from our profession on how to change the codes. We
need to do this.▪
About the author:
Chris Poland, S.E. is the Chairman and CEO of Degenkolb Engineers. A passionate seismic safety advocate, he actively participates in the academic, ethical and social advancement of his field. He is the 2006 recipient of the Alfred E. Alquist award from the California Earthquake Safety Foundation and is a member of the National Academy of Engineering. He can be reached at cpoland@degenkolb.com.
This article is available in PDF format:
Building Disaster Resilient Communities
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