What's New in Precast/Prestressed Concrete

Tornado Cannon Tests Precast Wall of Solar Decathlon House

Shooting 12-foot, 2x4 studs from a tornado cannon at wall sections sounds like fun. It is. And it’s loud. It’s also a serious way to demonstrate the durability and resiliency of precast concrete and showcase how to construct buildings to withstand wind-blown debris and the destructive force of high wind event storms, especially hurricanes and tornados.

In late June, Dukane Precast conducted such a demonstration at its headquarters in Naperville, IL, firing a series of high speed projectiles at wood framed, metal stud, brick-clad and precast concrete exterior wall sections. (See Note 1 below).

For the current test, to simulate flying debris that often become deadly missiles during a tornado or hurricane, 12-foot, 15-pound 2x4s were shot at three wall sections:

  1. A typical, residential vinyl-sided, wood-framed wall with ¾-inch exterior sheathening, R-19 interior insulation and ½-inch drywall. This wall section was shot with a stud projectile traveling at approximately 60 mph (equivalent to only an EF-1 or straight line winds). Just for fun, the cannon also fired a cabbage at the wall. These projectiles fully penetrated the wood framed wall section.
  1. A typical commercial building brick wall with 2x6 wood framing, 16-inches-on-centers, with ¾-inch sheathening, R-19 insulation, and ½-inch drywall. Again, the projectile sliced right through the wall.
  1. A duplicate of the precast concrete wall section being used on the Crete Solar Decathlon 2017 House (see below). This stud was shot at 100 mph, a speed that emulates an EF5 tornado with a 260 mph vortex (matching the FEMA 320 live wind test for a tornado shelter).

The projectile shot at the precast concrete wall shattered without penetrating or cracking the wall and barely leaving a mark.

A PCI Foundation Studio project

Attendees at the demonstration included several students and faculty from the International Center for Energy, Environment and Sustainability (InCEES) at Washington University in St. Louis, Mo. As part of a PCI Foundation Studio, these students are participating in the U.S. Department of Energy’s (DOE) Solar Decathlon 2017 program. (See Note 2 below).

A major reason for the Dukane demonstration, in fact, was to showcase the resiliency and durability of the precast concrete wall system being utilized for the University’s Solar Decathlon Crete House.

The DOE Decathlon program challenges collegiate teams to design and build full-size solar-powered houses. The Washington University team is designing a residence in Eureka, Mo. – the Crete House – as part of a master-planned net zero-energy village at Tyson Research Center in St. Louis. The home will first be built in St. Louis this summer. It will be de-constructed in October and re-constructed at the Solar Decathlon Village in Denver, Colorado, for the competition against 13 other university teams.

This all precast concrete demonstration home consists of precast concrete strip footing, a composite precast floor slab, precast wall panels, structural concrete roof panels and precast concrete gutters.

The home’s exterior wall featured in the tornado cannon demonstration consists of a thin wythe of Ductal, ultra high performance concrete (UHPC), a layer of expanded polystyrene insulation with Thermomass carbonfiber connectors, and an interior structural, reinforced concrete layer. Specially designed dry connection methods using bolts rather than welds will be used in the house construction to reduce field labor.

A primary goal of the student-designed home is to demonstrate how prefabricated, self-sustaining , and resilient homes can mitigate climate change. The home will also showcase the resiliency of precast concrete. As the Crete House promotion pamphlet states: "Precast concrete structures are inherently resilient, protecting against fire, moisture and mold, insects, seismic events and extreme weather conditions such as storms, strong winds and man-made phenomena such as blasts, force protection and acoustic mitigation."

Influencing the industry

Also attending the tornado cannon demonstration among the crowd of 100-plus persons were several dozen construction professionals, experts from the property insurance industry, and building and code officials from nearby Illinois cities and villages, including Naperville, Elgin, Oak Brook, Warrenville, Berkeley and Woodridge.

A secondary reason for the tornado cannon demonstration, according to Brian Bock, VP of Sales & Marketing for Dukane Precast, was to show these building industry representatives how buildings can be constructed to withstand the destructive forces of nature and provide resiliency in design.

The demonstration was effective, according to one attendee, Bill Novack, Director of Transportation, Engineering and Development (TED) for the City of Naperville, IL.

"It’s a fun demonstration to watch," said Novak following the stud cannon firings. "I think it’s great to actually see different products side by side. It’s also great to see that college students are looking at alternative materials and alternative ways of constructing the homes that we live in so that we can protect ourselves better in the future.

"We’re in an area where it [tornado damage] can definitely happen to us. So it’s good to see better building materials. Look at [recent deadly tornadoes in] Plainfield, Utica, Washington, and Coal City, Illinois.

"We often encounter new sorts of materials to consider for building," Novack added. "We update our building code every four to five years and it’s because of experiments [like this] and the hard work that these people put in that we have great alternatives to choose from and to specify going into the future."

 

 

NOTE 1. A similar tornado cannon test to demonstrate the storm resistance of precast concrete walls was conducted by Dukane Precast in 2007 at the Fortified Home project in Bolingbrook, IL. That test was held in cooperation with the Safe Home Illinois partnership, American Red Cross of Greater Chicago, and the Illinois Emergency Management Agency, with funding from PCI, Dukane and the Portland Cement Association. (See the video at: https://www.pci.org/Design_Resources/Building_Engineering_Resources/Design_for_Storm_Resistance/?terms=wind%20resistance).

NOTE 2. Participation by the University in the DOE program is being funded in part by PCI-IW, Dukane Precast, St. Louis Prestress, Lombard Architectural Precast Products, and US Formliner through a Studio of the PCI Foundation, as well as several contributors in PCI Central, PCI Midwest and PCI Mountain States regions. Sponsors of the Decathlon house include PCI, the PCI Foundation, Dukane Precast, Gate Precast, St. Mary’s Cement, LafargeHolcim, Ductal®, Enterprise Precast Concrete Inc., Lappco (Lombard Architectural Precast Products Co.), St. Louis Prestress Inc., US Formliner, Nawkaw, and Chicago Contractor’s Supply.

 

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