By Claude Goguen, P.E., LEED AP | Graphics courtesy Community & Regional Resilience Initiative (CARRI) (www.resilientus.org)
We’ve been hearing a lot about sustainable construction over the past few years. Now “resiliency” is the new buzzword. Sustainability and resiliency are actually complementary concepts, where resiliency relates to a more short-term recovery from a recent crisis while sustainability describes a long-term balance between consumption and resources. Resilient construction and development may seem like a new trend, but the concept has been around for many years.
What exactly is resiliency? According to the Department of Homeland Security (DHS), resiliency is the ability of any system (infrastructure, government, business and citizenry) to resist, absorb and recover from or successfully adapt to an adversity.
An “adverse occurrence” can refer to a range of various natural and man-made calamities including:
• Extreme weather (tornadoes, hurricanes or flooding)
• Geological (earthquakes, tsunamis and volcanic eruptions)
• Man-made crises (terrorism, war, forest fires, pandemics or large-scale industrial accidents)
• Economic (company closing, recession or depression)
Identifying the risk
Nearly every part of the U.S. has been affected by severe weather conditions. In fact, for most of the country, there are a number of natural hazards to be concerned with from hurricanes to earthquakes (see Figure 1).
The Institute for Business and Home highlights how natural disasters affect Americans:
• In 2006, 34.9 million people were seriously threatened by Atlantic hurricanes, compared with 10.2 million in 1950.
• Approximately 40% of the population resides in counties that face medium-to-high seismic risk.
• One-quarter of residents live in a county that has been ravaged by wildfire during the past 25 years.
• In 2008 alone, there were 16 major tropical storms (eight of which were hurricanes), 1,700 tornadoes, and widespread flooding (due to winter and tropical storms, spring melts, and other severe weather).
In fact, according to the National Resource Defense Council, 3,251 monthly weather records were broken in 2011 by extreme events that struck U.S. communities. Both the frequency and intensity of some extreme events are likely to worsen with continued climate change.
How resilient communities differ from the status quo
The Resilience Loss Recovery Curve (see Figure 2) helps explain how community function is affected by an acute disturbance (earthquake, chemical spill or hurricane) and depicts response and recovery curves. Community functions decline precipitously (blue and pink areas) as citizens respond to a disaster.
A more resilient community can more quickly restart vital local services (utilities, businesses, schools) and chart a path to a “new normal.” The more resilient community incurs some losses (blue area) but avoids additional losses (pink area), because it has taken informed measures (anticipating threats, disaster response plans and recovery strategies) to minimize the impact of the disturbance. Mitigation efforts of resilient communities include: improved land-use decisions and building code implementation; construction of resilient infrastructure; improved business and household planning to minimize loss; and a better orchestrated response of citizens and local agencies.
Resilient communities may find opportunities to transform themselves and grow. Thus, a resilient community’s “new normal” may be a higher level of function (Line A) or it may be able to return to a level of function existing before the disturbance (Line B). The key to disaster recovery is not only to get essential services back up and running, but also to get people back to work. That means buildings not only must resist the damages caused by an adverse event, but must be in a condition suitable to occupancy as soon as possible.=
Attributes of resilience
Key attributes of enhanced resilience are:
• Increased longevity
• Increased robustness
• Improved sustainability
• Improved life safety
• Increased durability
• Increased adaptability for reuse
• Increased resistance to disasters
Precast concrete has an excellent track record in all these categories. It does not rot or burn. It resists damage from flooding. It is extremely durable under the most extreme conditions, and has a service life that far exceeds most other building materials.
One of the ways to achieve enhanced resiliency is with a few modifications to existing model building code requirements. For example, current international building codes set the base flood elevation as determined by FEMA or local jurisdiction. The requirement for enhanced resiliency would set the minimum elevation at no less than 3 ft above the base flood elevation as determined by FEMA Flood Insurance Rate Maps.
According to studies by the National Institute for Standards and Technology (NIST) and the National Fire Protection Association (NFPA), functioning sprinkler systems (all but those rendered inoperable by human intervention) fail to operate when called upon by fire (fire large enough to activate sprinklers) more than 15% of the time. Thus, trade-offs in passive fire protection are not an acceptable practice for achieving enhanced resilience. Although it sounds like an oxymoron, the international building codes permit fire walls to be made of combustible materials. For enhanced resilience, fire walls must be constructed of noncombustible materials, and reductions in fire resistance ratings due to the presence of sprinklers must be prohibited.
Storm shelters have clearly demonstrated their ability to provide life safety during high wind events. FEMA advises that even for most tornadoes, there is usually at least five minutes notice to seek shelter. The international building codes reference design and construction criteria for storm shelters where present, but unfortunately do not provide guidance as to where storm shelters should be placed. Enhanced resiliency simply requires storm shelters for all buildings unless there is adequate, accessible shelter within ¼ mile.
What does this mean for you, the producer?
Assuming you produce a quality precast concrete product, there’s nothing for you to do to make your product more resilient. It’s inherent in precast concrete. But you must encourage these forward-thinking communities to adopt resiliency into their building specifications.
NPCA is travelling across the country participating in disaster-resistance workshops to further help community leaders recognize and assess local disaster risks they may face, evaluate mitigation measures based on the consequences and potential of those risks, understand the importance of incorporating fortified building programs into construction techniques, and to solidify their knowledge of safe rooms, storm shelters and disaster-resilient concrete systems such as precast concrete.
NPCA is a member of the Concrete Joint Sustainability Initiative (CJSI) and is also partnering with other concrete industry members to encourage enhanced resiliency.
Claude Goguen, P.E., LEED AP, is NPCA’s director of Technical Services.