Designing with concrete masonry can give buildings a chance to resist storms.
Throughout history, nature has impacted the way humans design our communities and buildings. From relatively routine considerations such as water tables and soil properties, to large events such as flooding and tornadoes, natural forces can easily overcome man-made designs. These design challenges have been most evident during large-scale events such as Hurricane Katrina, Superstorm Sandy, and the Northridge earthquake. In these types of events, the damage typically occurs quickly: lives lost, buildings collapsed, roads and infrastructure destroyed, utilities and basic services shut down. But the damage continues as these communities struggle for months and even years to try to regain what they had before the disaster.
In response, the term ‘resiliency’ has entered into our daily lexicon. The Federal Emergency Management Agency (FEMA) defines resilience as the ability to adapt to changing conditions and prepare for, withstand, and rapidly recover from disruption. Resilient communities proactively protect themselves from hazards, build self-sufficiency, and become more sustainable. Put simply, resilience is the ability to weather and “bounce back” from a disruptive event – as a neighborhood, community, or region.
The term is used in the context of mitigating social and economic disruptions in a community, as well as establishing programs and policies that attract businesses, reduce operating costs, and protect the environment through sustainable design and construction practices.
The focus on community resilience has been steadily increasing in recent years. Traditionally, community development has been guided by building code requirements. These provide a structure of provisions intended to protect the public’s health and safety. And as part of a larger strategy, they have succeeded–having a rigorous building code in place, combined with strong public policy programs, emergency response infrastructure, and advances in predicting and quickly responding to events has had a significant positive impact on the number of lives lost annually worldwide to natural disasters.
- Create strategies for local communities that are region and location specific
- Design and construct resilient buildings that are sustainable within the context of the larger community
- Refer to software programs and prediction models that anticipate the likelihood of risks at a specific location.
However, while the number of lives lost to natural disasters has continued to trend down, the cost associated with these events is trending up. According to data compiled by the National Weather Service and the Insurance Information Institute, the top ten costliest natural disasters since 1980 have caused more than $500 billion in damage (in 2013 dollars). In addition, we are seeing an increase in the number of natural disasters in recent years that cause more damage and impact larger populations. Part of this is due to our population distribution: in 1913, about 10 percent of the world’s population lived in cities. Today that figure is 50 percent, and by 2050, it is expected to be 75 percent. So, even if the same level of natural disaster occurs today as occurred in 1913, many more people are likely to be impacted. As a result, many communities are unable to recover from an extreme event without government support and intervention.
This is leading to a shift in societal expectations. Although building codes continue to become more comprehensive and rigorous, there is a growing awareness that the minimum requirements in the codes need to be augmented with policies and programs to protect personal property and the future viability of our communities.
While major natural disasters such as Katrina, Sandy, and Northridge do not occur every year, they do occur frequently enough and across a large enough geographic area that few communities remain unaffected. When we factor in wildland fires and extreme storms, everyone within the U.S. is subject to the whims of nature’s wrath. It is clear we need to re-evaluate how we respond to disasters on a community level. The built environment
True community resiliency encompasses a broad spectrum of social and policy components, including land use and urban planning, robustness, redundancy, a sense of community, response procedures and technologies, and strategies for recovery. From a building and infrastructure perspective, resiliency addresses several key attributes, including increased:
- Life safety
- Adaptability and reuse, and Disaster resistance.
The Institute for Business and Home Safety has developed the FORTIFIED programs that identify specific risks in a given location and tailor design and/or construction recommendations to mitigate the impact of the event. There are currently three programs in use:
- FORTIFIED Home – for existing residential construction
- FORTIFIED for Safer Living – for new residential construction, and
- FORTIFIED for Safer Business – for new commercial construction.
Thirteen homes on the Bolivar Peninsula in Texas designed and built using FORTIFIED concepts and strategies survived Hurricane Ike, which slammed into the peninsula along with a nearly 20-foot (6.1 m) storm surge in September 2008. The homes designed under the FORTIFIED approach were the only structures left standing on Bolivar Peninsula for miles around, precisely because they were specifically designed and built to withstand extreme wind and water damage.
Concrete masonry for resilient communities
What role can building materials play? Concrete masonry construction has inherent strength, durability, fire resistance, impact resistance, longevity and rodent resistance all of which contribute to the resiliency of the built environment. In short, it offers inherent resiliency at an economical cost: a look at more than 40 metropolitan cities around the country showed the cost of loadbearing masonry to be between -4 percent and +5 percent of the next lowest cost alternative (www.pafscac.org).
For these reasons, concrete masonry has been the traditional choice for hospitals, police departments, schools, storm shelters and other essential buildings. Concrete masonry buildings have weathered earthquakes, hurricanes, fires and floods.
In May 2011, the tornado that ripped through Joplin, MO, left a path of destruction about 1 mile (1.6-km) wide and 6 miles (9.7 km) long, killing 161 people and destroying thousands of buildings. The National Weather Service classified the Joplin tornado as an EF-5, with peak winds of more than 200 mph (90 m/s). According to the National Institute of Standards and Technology, over 80 percent of the deaths were attributed to building collapse. Economic losses were estimated at over $2.8 billion.
Extreme windstorms in many parts of the country, such as hurricanes and tornadoes, pose a serious threat to buildings and their occupants. Although current building codes do a good job addressing the effects of earthquakes, fires and hurricanes on buildings, the extreme wind speeds and accompanying debris from tornadoes are not currently covered. Beginning with the 2015 International Building Code, however, storm shelters will be required for most educational facilities in high-risk tornado regions.
Tornadoes produce wind pressures and generate flying debris at much higher levels than those used to design most commercial and residential buildings. Although it is possible to build tornado-proof buildings, doing so on a communitywide scale is not economically feasible. The approach is to design storm shelters to provide life safety and accept the loss of buildings and property in the event of a tornado.
Storm shelters are buildings or parts of buildings designed and built specifically to provide a highly protected space where community members or occupants can safely ride out the storm. There are two types of shelters: community shelters, buildings specifically dedicated to provide temporary shelter during a storm, and residential shelters, which are typically reinforced rooms within a home, where the occupants can safely seek refuge during a hurricane or tornado.
General design considerations for storm shelters include:
- Adequate wall and roof anchorage to resist overturning and uplift
- Walls and ceilings, as well as openings such as doors and windows, that withstand design wind pressures and penetration by flying debris
- Connections between building elements that are strong enough to resist the design wind loads
- Foundations that are sized to resist the design overturning and uplift forces.
Typical concrete masonry storm shelter walls are constructed of fully grouted 8-inch (203-mm) concrete masonry with vertical reinforcement at least every 48 inches (1220 mm) on center. The fully grouted masonry provides impact protection from flying debris, and is heavy enough to resist overturning for the most severe tornado loading, based on a 250 mph (112 m/s) wind speed. For smaller shelters, such as 8 ft x 8 ft (2.4 m x 2.4 m) or lower design wind speeds, solidly grouted 6-inch (152-mm) walls are adequate. An impact-rated door is used, whose frame is grouted into the adjacent masonry. The masonry walls are anchored into concrete floor and roof systems to provide structural continuity. Wildfires Masonry’s inherent redundancy and fire resistance has also been tested in extreme events. For example, the 90 West Street Building, a designated New York City landmark, was built in 1907 to house offices for shipping and rail companies. It was still in use as an office building on September 11, 2001, and close enough to the World Trade Center that debris from the South Tower destroyed the roof, damaged the façade and led to a fire that raged uncontrolled for five days. And yet the building not only survived, renovation was possible. The office building was converted into 410 apartments and, four years after the disaster, the building was reopened.
In areas prone to wildfires, buildings may be subject to extremely high temperatures, but typically only for short periods of time. Protection of these structures focuses on providing buffers around the building, such as driveways and other areas clear of vegetation, using ignition-resistant exterior materials and limiting vent locations. For exterior walls, the FORTIFIED program calls for a noncombustible building envelope with a minimum fire resistance rating of one hour. This is an easy requirement for concrete masonry to meet: all hollow units at least 6 inches (152-mm) thick will exceed a one-hour rating, and many 4- inch (102-mm) thick units will as well. Summary The concept of functional resilience encompasses a broad range of social, political, and legislative topics. However, choices made when designing our homes and commercial buildings can impact a community’s functional resilience by helping ensure our buildings perform well and remain functional during and after natural disasters.