Ashraf El Damatty is hoping a mesh of wire cables installed on the roof of a home will give it the strength to withstand severe windstorms – and possibly hurricanes. So far the tests have proven him right.
The Civil & Environmental engineering professor at The University of Western Ontario has partnered with M.A. Steelcon Engineering Ltd. to develop the “Hurricane Resistance System” for wood framed homes to help prevent them from collapsing during severe windstorms and hurricanes.
On Monday, June 27, El Damatty put his theories to the test using full-scale roof trusses outfitted with the Hurricane Resistance System in the Structural Laboratory at Western. The trusses were put under pressure by hydraulic jacks applied to the underside to simulate the vacuum-like uplift winds of a hurricane.
“We are trying to simulate the uplift force that happens to the roof of houses when they get subjected to a strong windstorm, says El Damatty. “What we expect is that once we put on this mesh … the house would become twice stronger in resisting the wind forces.”
During a previous test on the tresses conducted without the system installed, the roof was able to withstand about nine kilonewtons (equal to about 2,000 pounds) of force.
Although the nails on the trusses pulled away from the supporting wall structure creating a gap during Monday’s test, the wire mesh kept the roof intact, preventing it from flying off during a wind storm. The tests were stopped at 19 kilonewtons but the wire cables continued to hold tight.
This means, says El Damatty, the house could withstand more than 60 per cent stronger wind speeds it could without the Hurricane Resistance System. “If a house can sustain, let’s say 30 miles per hour, now it can go up to about 50 miles per hour,” he says.
“We started to get openings,” he says, pointing out the space created between the trusses and the supporting wall. “We have six connections. All of them were maintained and we have separation in only one connection.”
The design of the system includes several wire cables running parallel with the roof attached to a steel beam, which would be installed around the perimeter of the building and would help share the load equally across all the wires. The wires are then connected to the ground using piles (a post-like foundation).
The researchers are exploring the possibility of developing a mesh design with the wires, which would help protect against changing wind directions.
The system, which can be retrofitted to install on the roof of existing homes, would help prevent houses from collapsing during severe windstorms and hurricanes. Often in high winds, the roofs are lifted off buildings and the walls become laterally unsupported, causing them to collapse.
This system of protection is particularly marketable in areas of North America and several island nations ravaged by tornadoes and hurricanes each year.
Most of the homes built in North America use wooden frames, mainly due to its light weight, low cost and availability.
In areas subject to hurricanes, most new structures are built with a hurricane clip, which is a steel clip connected to the trusses and top plate of the wall. But this could not be applied as a retrofit to older homes. As well, building codes in Canada do not require a hurricane clip, notes Ryan Jacklin, a master’s student in civil and environmental engineering involved in the research.
“This connection is still vulnerable today in Canadian houses,” says Jacklin.
The president of St. Catherines-based M.A Steelcon Engineering Ltd., Michael Schor, visited Western to witness the test.
Schor dreamed up the idea after seeing the devastating destruction of Hurricane Katrina. He approached El Damatty and the pair developed a partnership to design, build and test the validity of the system.
“There must be something we can do to improve the structure of small houses,” says Schor, whose company mainly designs high-rise buildings. “Because most of the houses are made out of wood, this is why they need this.”
While Monday’s test was considered a success, the system is still not ready to go to market.
“We have applied vertical force consistently and that affected the weakest connection. But in reality, the way I see it, wind will change directions many times,” notes Schor.
The researchers would like to conduct a full-scale test of the system using Western’s Insurance Research Lab for Better Homes, otherwise known as the Three Little Pigs facility to see how the system reacts on a full-size housing structure.