By Claude Goguen, P.E., LEED AP
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.
But what exactly is resiliency?
To those unfamiliar with this terminology, a familiar sports example might help. In the recent Kentucky Derby, “I’ll Have Another” was a 15-to-1-shot colt ridden by a rookie jockey, who resisted the turbulence and dangers of the mid-pack to emerge as the winner in the final stretch. This unheralded colt and jockey had the resiliency to bounce back in extreme adversity because of excellent anticipation, strategy and training for this singular event. Likewise, resiliency can be defined as the adaptability of a system (communities or buildings) to maintain its functions and structure in the face of turbulent internal and external change.
The key attributes of enhanced structural resiliency are improvements in:
1. Longevity (service life)
2. Robustness (minimized potential for structural progressive collapse)
4. Life safety
6. Adaptability for reuse
7. Resistance to disasters
Community resiliency has been defined as the “capability of a community to anticipate risk, limit impact, and recover rapidly through survival, adaptation, evolution and growth in the face of turbulent change.”1 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.
“Turbulent change” and “adversity” can refer to a range of various natural and man-made calamities including the following:
• 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)
A community’s ability to recover from these events depends on many factors. The effects of the first three categories can be minimized with conscientious construction methods using durable, strong materials. Precast concrete is an example of such a material that is designed to absorb large static and dynamic loads, and resist damage due to flooding and fires.
Local reaction preferable to government response
Historically, the United States has drawn on the strength of its citizens in times of crisis. However, as the threats have expanded and grown more complex, Americans have been moving to the sidelines, allowing government agencies to issue warnings, monitor threats and deploy resources. Many agree that this is a trend that must be reversed. Too much reliance on federal agencies such as the DHS, the Federal Emergency Management Agency (FEMA) and the military can be detrimental to a quick and thorough recovery. The reaction of local communities after a disaster can play a critical role and avoid overdependence on limited government resources. Further, local building codes can ensure resiliency by mandating resilient structural designs for new construction.
Who is at risk?
Nearly every part of the United States 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).
Some scientists believe that the frequency and intensity of extreme weather are likely to worsen with continued climate change (global warming).
How resilient communities differ from the status quo2
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 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 both 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.
Recommended post-disaster recovery times
The San Francisco Planning and Urban Research Association evaluated buildings in various categories from police and fire departments to hospitals to schools (see Figure 3). This evaluation shows recommended time lines (arrows) for reoccupation and functionality/service for a minimum level of community resilience after a disaster. Notice, for example, that hospitals and police and fire departments must be functional immediately after an adverse event in a resilient community.
Building codes: first line of defense against disaster
Floods: 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.
High winds: Damage from wind hazards is not only important for the performance of a building, but when failures occur, debris also can damage nearby structures and pose an increased threat to human life. The requirement for enhanced resiliency would require that basic wind speeds be increased by 20 mph for design purposes.
Fire sprinklers: Fire sprinklers, while not always capable of extinguishing or controlling fires, have clearly proven to increase evacuation time. In fact, the ICC4 codes now require automatic sprinkler systems in most occupancies and even in one- and two-family dwellings. The criteria for enhanced resiliency simply extend the requirement for sprinklers to all buildings except low-hazard factories and storage facilities.
Storm shelters: 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.
Shelter from tornadoes: federal standards for safe rooms
The horrific devastation in Tuscaloosa, Ala., and Joplin, Mo., with a loss of more than 400 people, made 2011 the deadliest year for tornadoes in the United States since 1936. More than 1,500 confirmed tornadoes took some 550 lives and caused billions of dollars in damages. There has to be a better way to protect people from these storms. Certified and approved precast concrete safe rooms and storm shelters provide a secure area and peace of mind for families and communities when severe weather threatens.
To ensure that safe rooms are structurally sound units that provide near-absolute protection from adverse elements, FEMA has developed design, construction and operation criteria for architects, engineers, building officials, local officials, emergency managers and prospective safe room owners/operators. Two design guidelines are FEMA 320 and FEMA 361. FEMA 320 outlines the design criteria for residential safe rooms (up to 16 occupants), while FEMA 361 covers the development of public and community safe rooms.
Using FEMA guidelines as a standard, design and construction professionals led by the ICC and the National Storm Shelter Association (NSSA) have joined forces to produce the first ICC/NSSA Standard for the Design and Construction of Storm Shelters (ICC-500). Manufacturers of products meeting this standard assure prospective owners that their safe rooms will be able to provide life-safety protection. While fully supporting this effort, FEMA has continued to promote FEMA 320 and FEMA 361 guidelines to communities and individuals seeking further guidance.
Precast concrete safe room design meets federal standards5
Precast concrete safe rooms and shelters are classified according to location: aboveground (stand-alone) or in-ground (internal safe room). Each has several inherent advantages.
When designing a precast concrete safe room, structural integrity is the primary design consideration. Although human safety and health are fundamental to design, the first consideration should be a structurally sound unit that can withstand the direct and secondary forces of wind and windblown debris.
FEMA 320, FEMA 361 and ICC-500 outline the design requirements for the main wind-resisting structural system and components as well as cladding of these precast units. Standards also cover safety and health considerations such as lighting, ventilation, sanitation, fire safety, means of egress and minimum floor space.
Since tornadoes are typically short-term events, comfort is not a major factor in design, although precast concrete safe rooms provide additional comfort over other safe room designs in terms of ventilation, insulation and ease of installation. FEMA and ICC state that safe rooms designed to withstand tornadoes must provide a minimum of 5 sq ft of floor area per person. For long-term events, a minimum of 7 sq ft to 20 sq ft of floor area per person is required.
Resilient rebound of Greensburg, Kansas
For a real-world example of how a community came together to bounce back from a disaster and adopt resilience in their rebuilding, one only has to look to Greensburg, Kansas.
At 9:50 p.m. on May 4, 2007, an EF56 tornado leveled the city of Greensburg, totally destroying its infrastructure and more than 90% of its homes and buildings. While the average tornado is less than 50 yds across, this monster storm produced a twister that was 1.7 miles wide as it barreled through town with gusts exceeding 250 mph. Fortunately, Greensburg’s citizens were given 20 minutes of warning that a big storm was coming, thanks to the National Weather Service, which upgraded the storm from a tornado warning to an “emergency,” emphasizing the magnitude of its power. Eleven people lost their lives in the Greensburg tornado. It was estimated that if the storm had occurred later that night, hundreds of casualties might have occurred.
Rebuilding with precast concrete resiliency
In the days immediately following the storm, several entities simultaneously had the notion to rebuild the community in a sustainable and resilient manner. Local leaders started meeting in a tent and residents came up with the idea to rebuild as “America’s model green community” and “Greensburg Greentown” was born.
The city’s public works building was rebuilt on the site of the old power plant after the tornado, earning LEED Gold certification. The building envelope is precast concrete.
The Twilight Theatre, originally built in 1917, will be rebuilt as the all-new “Twilight Theatre & Community Auditorium” and will make use of modern construction methods and materials including precast concrete that support long-term sustainability, exemplifying standards for energy efficiency and resource conservation.
Resiliency and the role of precast concrete
While the challenges facing communities wishing to improve their resilience to natural and man-made disasters are significant, the benefits, in terms of saving lives and property, can be immeasurable. As the new construction in Greensburg’s rebound illustrate, precast concrete systems are the preferred choice for resilient communities and structures.
Precast concrete has a solid track record for ensuring the fore-mentioned attributes of resiliency: long service life, robustness, sustainability, life safety, durability, recyclability and resistance to disasters. These are the many reasons communities across the United States are choosing precast concrete to protect their infrastructure, businesses, and homes and loved ones.
1 From the Community and Regional Resilience Institute (CARRI)
2 From the Community Resilience System Initiative (CRSI) Steering Committee Final Report by Community and Regional Resilience Institute (CARRI)
3 For more information, see “The Resilient City” at www.spur.org/files/u7/RC-overarching.pdf
4 International Code Council (ICC)
5 Visit http://precast.org/2011/09/shelter-from-the-storm for Evan Gurley’s article on precast concrete safe rooms in the September-October issue of Precast Inc. magazine.
6 Enhanced Fujita Scale (EF5)
NPCA is a member of the Concrete Joint Sustainability Initiative (CJSI) and is partnering with other concrete industry members to encourage enhanced resiliency. For questions about this article, please contact Claude Goguen, NPCA’s director of Technical Services, at (317) 571-9500 or [email protected]