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Concrete Homes - What the Research Says
Wind Testing Shows How Concrete Walls Hold Up in a Hurricane
by Jackie Craven
When hurricanes and typhoons
howl, the greatest danger to people and property is flying debris.
Carried at such intense
velocity, a 2 x 4 piece of lumber will become a missile that can slice through
walls.
When an EF2 tornado moved
through central Georgia in 2008, a board from an awning was ripped off, took
flight across the street, and impaled itself deep into an adjacent solid
concrete wall.
FEMA tells us this is a
common wind-related event and recommends the building of safe rooms.
Researchers at the National
Wind Institute of Texas Teach University in Lubbock have determined
that concrete walls are strong enough to withstand flying debris from
hurricanes and tornadoes.
According to their findings,
homes made of concrete are much more storm-resistant than houses constructed of
wood or even wood studs with steel plates. The ramifications of these research
studies are changing the way we build.
The Research Study
The Debris Impact Facility at Texas Tech is well-known for
its pneumatic cannon, a device capable of launching various materials of
different sizes at different speeds. The cannon is in a laboratory, a
controlled environment.
To duplicate hurricane-like
conditions in the laboratory, researchers shot wall sections with 15-pound 2 x
4 lumber "missiles" at up to 100 mph, simulating debris carried in a
250 mph wind.
These conditions cover all
but the most severe tornadoes. Hurricane wind speeds are less than the speeds
modeled here.
Missile tests designed to
demonstrate damage from hurricanes use a 9-pound missile traveling about 34
mph.
Researchers
tested 4 x 4-foot sections of concrete block, several types of insulating
concrete forms, steel studs, and wood studs to rate performance in high winds.
The sections were finished as
they would be in a completed home: drywall, fiberglass insulation, plywood
sheathing, and exterior finishes of vinyl siding, clay brick, or stucco.
All
of the concrete wall systems survived the tests with no structural damage.
Lightweight steel and wood stud walls, however, offered little or no resistance
to the "missile." The 2 x 4 ripped through them.
Intertek,
a commercial product and performance testing company, has also done research
with their own canon at Architectural Testing Inc.
They point out that the
safety of a "concrete home" can be deceptive if the house is built
with unreinforced concrete block, which offers some protections but not
total.
Recommendations
Reinforced concrete homes have proven their wind-resistance
in the field during tornadoes, hurricanes, and typhoons.
In Urbana, Illinois, a home
constructed with insulating concrete forms (ICFs) withstood a 1996 tornado with
minimal damage.
In the Liberty City area of
Miami, several concrete form homes survived Hurricane Andrew in 1992.
In both cases, neighboring
homes were destroyed. In the fall of 2012, Hurricane Sandy blew apart the older
wood construction homes on the New Jersey coast, leaving alone the newer
townhouses built with insulating concrete forms.
Monolithic domes, which are
made of concrete and rebar in one piece, have proven especially strong.
The sturdy concrete
construction combined with the dome shape make these innovative homes nearly
impervious to tornadoes, hurricanes, and earthquakes.
Many people cannot get over
the look of these homes, however, although some brave (and wealthy) homeowners
are experimenting with more modern designs.
One such futuristic design
has a hydraulic lift to actually move the structure below the ground
before a tornado strikes.
Researchers
at Texas Tech University recommend that houses in tornado-prone areas build
in-residence shelters of either concrete or heavy gauge sheet-metal.
Unlike hurricanes, tornadoes
come with little warning, and reinforced interior rooms can offer more safety
than an exterior storm shelter.
Other advice researchers
offer is to design your home with a hip roof instead of a gable roof, and
everyone should use hurricane straps to keep the roof on and the timbers
straight.
Concrete and Climate Change — More Research
To make concrete, you need cement, and it's well-known that the
manufacturing of cement releases great amounts of carbon dioxide into the
atmosphere during the heating process.
The building trade is one of
the largest contributors to climate change, and cement makers and the people
who purchase their product are some of the largest contributors to what we know
to be "greenhouse gas pollution."
Research on new production
methods will no doubt be met with resistance from a very conservative industry,
but at some point consumers and governments will make new processes affordable
and necessary.
One
company trying to find solutions is Calera Corporation of California.
They have focused on
recycling CO2 emissions
into the production of a calcium carbonate cement. Their process uses the
chemistry found in nature — what formed the White Cliffs of Dover and the
shells of marine organisms?
Researcher
David Stone accidentally discovered an iron carbonate-based concrete when he
was a graduate student at the University of Arizona.
IronKast Technologies, LLC is
in the process of commercializing Ferock and Ferrocrete, made from steel dust
and recycled glass.
Ultra-high-performance
concrete (UHPC) known as Ductal ® has been used successfully by
Frank Gehry in the Louis Vuitton Foundation Museum in Paris and by
architects Herzon & de Meuron in the Pérez
Art Museum Miami (PAMM).
The strong, thin concrete is
expensive, but it's a good idea to watch what the Ptizker Laureate architects
are using, as they are often the first experimenters.
Universities
and government entities continue to be the incubators for new materials,
researching and engineering composites with different properties and better
solutions.
And it's not just
concrete - the U.S. Naval Research Laboratory has invented a glass
substitute, a transparent, tough-as-armor ceramic called spinel (MgAl2O4).
Researchers at MIT's Concrete
Sustainability Hub are also concentrating their attention on cement and
its microtexture - as well as the cost-effectiveness of these new and
expensive products.
Why You Might Want to Hire an Architect
Building a home to withstand nature's fury is not a simple task.
The process is neither a construction nor design problem alone.
Custom builders can
specialize in insulated concrete rorms (ICF), and even give their end-products
safe-sounding names like Tornado Guard, but architects can design beautiful
buildings with evidence-based material specifications for builders to use.
Two questions to ask if you
are not working with an architect are
1.
Does the construction company have architects on staff? and
2.
Has the company financially sponsored any of the research testing?
The professional field of
architecture is more than sketches and floor plans. Texas Tech University even
offers a Ph.D. in Wind Science and Engineering.
Jackie Craven
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