A New Material Developed at UMaine Could Withstand more Hurricane Damage
The researchers began exploring ways to safeguard buildings soon after Hurricane Andrew ripped Florida apart in 1992 and caused $20 billion in damages.
Professor Habib J. Dagher and Associate Professor William Davids at UMaine’s Advanced Engineered Wood Composites Center hold two patents on a product they developed there that they say will help keep houses together through hurricanes and even through other disasters like earthquakes.
They call the disaster-resistant material “advanced oriented strand board,” or “AOSB,” and Dagher and Davids are now working with a leading industry group to test the material further and see about getting it into high-volume manufacturing and, ultimately, into the marketplace.
Simply put, the professors and their students developed a resin- and-fiberglass composite strip that can be layered into oriented strand board, a common building material normally referred to as “OSB.”
In tests at UMaine, the AOSB has shown a 125 percent increase in strength for one type of failure during a hurricane over traditional OSB, and a 73 percent increase in a building’s ability to absorb energy and not shake apart during an earthquake.
For the engineers, the project offered a chance to go beyond existing materials in a new way, to actually create something new that may keep people safe from the harshness of nature.
“Engineering is an inherently creative profession. It tends to be viewed as a very geek-centric, black-and-white, mathematic type of thing, but the creative comes in new designs, (building) better mousetraps,” said Davids. “This particular project involved a lot of really interesting engineering, thinking outside the box. We hold the patents, so it kind of crosses the line to inventor, but I don’t think of myself as an inventor.”
To come up with a solution, Dagher and Davids first had to understand the problem – exactly what happens to houses in a hurricane? They found two major building failures.
The first is that the panels of OSB get sucked off the roof by negative pressure. The wind whipping over the roof creates a negative pressure that pulls the panels right off. The nails that hold the panels to the joists stay embedded in the joists – the nail heads pull right through the OSB as it goes flying into the storm.
That particular failure leaves the house vulnerable to the torrential rains of a hurricane, ruining the contents of the home.
The second failure is more structural in nature.
Picture a home as a box. Winds pushing on one side of the box will put pressure on the two adjacent sides – the ones parallel to the wind – which are called “shear walls.” The square shear walls basically try to become parallelograms under the pressure. It’s called “racking.”
The 2-by-4 framing alone would allow this racking to happen, which would mean a collapse of the whole structure. But the OSB sheathing panels nailed to the house frame keep the walls square; they don’t rack like the framing would.
However, under hurricane-force wind, the racking of the frame can actually cause the nails holding the frame to the panels to tear through the OSB.
The OSB itself, as a material, isn’t the problem, said Dagher.
There are several factors at play that exacerbate the problems with both types of failure. The first is the common use of high- impact nail guns in carpentry today. The force of the nails being shot into the OSB actually breaks the wood fiber around each nail, severely weakening the material.
On the shear wall problem, the OSB panels are nailed onto the 1 1/ 2-inch-wide edges of studs. There are two panels nailed onto each stud; the nails must be put into the panels about 3/8 of an inch from the edge to hit the stud. That little bit of distance from the edge makes it even easier for the nails to tear through the OSB, Dagher said.
In the case of the roof problem, or the “nail head pull-through” failure, rain poses a particular issue. Before the panels are sucked off, the roof shingles normally fly away. That leaves the OSB open to the soaking rain, which weakens the wood, making it that much easier for the panels to pull through the nails.
But the primary issue with both types of failure is simply a lack of nails, said Dagher. In hurricane-prone areas, contractors are supposed to use about 100 nails per panel of OSB – that would put a nail every 3 inches around the edges.
“How many contractors are going to do that?” Dagher asked.
The average is between 20 and 30 nails per panel, Dagher said.
But it’s impossible to address the problem of too-few nails head- on, said Dagher. There’s no real way to assure that contractors put 100 nails into each panel.
‘LIKE DUCT TAPE’
So Dagher and Davids approached the problem sideways – by making OSB stronger.
They experimented with a number of resins and fibers before settling on the current combination. The fibers are geometrically arranged in the resin to provide the greatest tensile strength, or resistance to lengthwise stress. OSB is made of wood chips that are oriented in different ways to improve various strengths, infused with a resin, heated and pressed together.
The AOSB looks the same, but a cross section of a 1/2-inch- thick piece of the board reveals an 1/8-of-an-inch layer of the resin-and-fiber composite sandwiched in the middle.
The material can be punctured by a nail with ease, but has a tensile strength greater than steel, Dagher said. It limits the damage from a nail gun, and forces nails to bend and stretch during heavy winds, rather than rip through.
The strips only run a few inches along the edge, where the extra reinforcement is needed. They tested the AOSB repeatedly on the massive measuring equipment at the wood lab at UMaine, putting not only individual pieces through their paces, but entire walls made of the material, as well.
They have two patents on the product. One involves using a roll of the composite to reinforce an existing house when contractors are reshingling or putting new siding on.
“It’s like duct tape – but it’s a duct tape stronger than steel,” said Dagher.
The other patent deals with using the material for new construction.
Dagher and Davids have signed an agreement with the Engineered Wood Association, an industry trade group, to get the product tested outside of UMaine’s labs, and to try to introduce it into a production line. The integration into OSB production must be seamless – adding virtually no time to the manufacturing process.
“The issue is the cost, and how to (put the) product into production, how to make it in a commodity type of production,” said Borjen Yeh, director of technical services at the association. “The market will decide whether the material is needed; the technology itself certainly has its merit.”
Davids said they’ve estimated using AOSB on a 3,000-square-foot home would add between $800 and $1,000 onto the total cost.
“That’s a good guess, but it’s a guess,” Davids cautioned.
A MILITARY ANGLE
The ultimate goal would be to have some company license the technology from UMaine, with the fees coming back to the school, said Dagher. There may be some chance to transfer the technology to a Maine company, but there are few OSB plants in the state, and costs to ship AOSB to disaster-prone areas may make it economically unsound.
But even if AOSB isn’t made in Maine, there’s still a value to the state, suggested Janet Yancey-Wrona, director of the state Office of Innovation.
“If you have some company using this technology down in Louisiana, but it’s University of Maine technology, it starts to get the word out that we have this world-class research facility,” said Yancey-Wrona. “Even if it doesn’t directly create jobs at a company in Maine, there are other economic development benefits.”
The military is also looking at the AOSB, said Dagher, and has funded the center with a $2 million grant for a one-year project to explore using the material to develop portable temporary shelters for troops that are blast- and ballistics-resistant.
The engineers and their students have done some work on the military project already; Dagher has a sheet of the composite material, 16 layers thick, that stopped five 9mm bullets traveling at 1,350 feet per second. The disaster-resistant AOSB uses only one or two layers of the composite, for comparison.
The military would like to have shelter kits made with such building materials, and that could provide opportunity for Maine companies, said Dagher. The kits would essentially be a shelter-in- a-box, easily assembled and taken down, and they could be made anywhere and sold to the military.
They’ve got a prototype shelter set up in the lab, made with traditional OSB. Now that they’ve figured out how to make the shelter, they’re going to make one with AOSB.
The project is one of many at the Advanced Engineered Wood Composites Center that is in a pipeline toward commercialization.
“One of the top recommendations from the Sustainable Forestry Study and the Future Forest Study is better connection between the Maine wood industry and the research and development going on at UMaine – this is an example of those kinds of connections,” said Yancey-Wrona.
An added benefit of the AOSB project, said Davids, is that there’s a real potential the material could save property, and possibly lives.
“The economic development in the state is always a primary consideration, but equally important would be the benefit to society,” said Davids. “Any engineer always works with that in mind.”