Making magic with wood UM professor engineers feats with composites
By Susan Young
Carefully perched on a rock, Habib Dagher tapped away at the keys of a laptop computer balanced on steel rods protruding from a small wooden bridge. A piece of plastic shower curtain, decorated with a colorful children’s motif, shielded him from the pouring rain.
Not exactly the glamorous life some would expect of the head of a nationally renowned research program. But for Dagher, director of the University of Maine’s Advanced Engineered Wood Composites Center, it’s just another day of data collection.
What is out of the ordinary is the 16-foot bridge on Washington Street in Milbridge that Dagher is inspecting. Although it is short and doesn’t look like much to the casual passer-by, it is one of a growing number of timber bridges in Maine.
The bridges, some as long as the 192-foot span from nearby Addison to Crowley Island, are made of low-grade wood which has been reinforced with a composite material. The wood beams, which are reinforced with a thin strip of fiberglass reinforced man-made polyfibers, are significantly stronger than plain wood, especially such low grades as Eastern hemlock and red maple.
What is unusual about the Washington Street bridge is that it is the only timber bridge in the world that is held together by composite rods. Previous bridges have had steel rods.
A dozen narrow rods run the width of the bridge. Both ends of the rod are capped with a composite plate that is held on by a metal bolt. The bolts are tightened to exert 10,000 pounds of pressure thereby squeezing the bundles of composite reinforced planks together.
This eliminates the need for nails to hold the planks together. Nail holes create openings where water can enter and rot the wood. Nails also work their way out of their wood holes over time. Eliminating steel rods also gets rid of another part of the bridge that would be susceptible to corrosion.
The composite rods on this bridge are temporarily capped with lengths of steel because the bolts cannot be threaded onto the composite material. The lengths of steel, which are not integral to the bridge, will eventually be cut off.
For now they provide the perfect place for Dagher to balance his computer. On a recent rainy afternoon, he and two graduate students visited the bridge to gather data to determine if it is performing as expected.
Sensors measure the amount of stress placed on three of the rods. That information, along with the temperature of the wood and the surrounding air, is automatically fed into a brown metal box every hour. Dagher and his students visit the bridge periodically to feed the stored data into a laptop computer. The data is analyzed back at the Orono campus where Dagher teaches civil engineering courses when he isn’t designing and testing wooden bridges.
UM’s leadership role
The bridges have become an almost all-consuming passion for Dagher. He talks about them to Rotary Clubs and engineering conferences around the world. He flies across the country almost monthly to meet with wood and composite industry officials to learn how to improve the university’s product.
His diligence has paid off. The university’s Advanced Engineered Wood Composites Center, which Dagher oversees, was recently awarded a $4.2 million grant from the National Science Foundation. The money will be used to buy equipment and hire personnel. Two new professors who were hired with the grant money are arriving on campus this month.
In addition, the center received $2.2 million from the U.S. Department of Commerce to build a laboratory to test full-sized bridges. Ground will be broken for construction of the building, which, naturally, will be made of wood-composite material, early this fall. To date, testing has been done in an aged steel frame in the engineering building, in the basement of other campus buildings and in a cramped wooden shed next to the university dump.
The grants have propelled the university into a national leadership role in wood composite research. That’s no small feat considering the industry leaders and most of the other universities involved with wood composites are located on the West Coast.
“The U.S. industry looks at the University of Maine as one of two focal points for this technology,” said Tom Williamson, executive director of the American Plywood Association in Tacoma, Wash. The other focal point is Oregon State University, home of a leading professor in the development of wood composites.
He admitted he originally thought it was a bit “bizarre” that the country’s leading wood composite research facility would be on the East Coast while the major industry players are in Washington and Oregon. But, he said, he has come around.
“The University of Maine is extremely important,” Williamson said. He said a year ago he wouldn’t have considered the university as a major player but because of its continuing work and the NSF grant, the Orono campus is now a leader in the drive to help the wood product industry remain competitive with steel and other building materials.
On Friday, a meeting will be held on the Orono campus to interest local business and community leaders in the fledgling industry. UM has two patents pending for the wood composite technology and hopes to license commercial manufacturing rights to private companies in the area.
In October, wood and composite industry officials and researchers will convene at UM for a wood composite summit.
During its years of financial hardship, UM almost lost the federal wood composite funding because the campus was unable to come up with the necessary matching money. University of Maine System Chancellor Terry MacTaggart, recognizing the project’s potential, stepped in and came up with the needed funds.
He and others point to the timber bridge project as an example of research that has clear-cut economic benefits for the state of Maine.
“Habib’s stuff is the way things ought to be,” said Dan Dwyer, UM’s vice provost for research. He said the timber bridge project has the potential to spark a lot of economic development in Maine. He said it would be great to see several wood laminating plants in the state. The only one in Maine now is in Mechanic Falls.
In addition, the wood composite project allows students to gain first-hand experience in a growing industry.
“It’s a win-win situation when it comes to research,” Dwyer said.
The project began a few years ago when Dagher and several colleagues looked for ways to strengthen Maine’s low-grade woods so they could be used for industrial projects.
“We wanted to make stronger wood. We can’t grow stronger trees,” Dagher said.
The idea of making wood stronger is not new. Early navies, for example, used metal plates over their ships’ wooden hulls to deflect cannon balls. The problem with wood-metal composites is that they eventually separate.
So the first problem the researchers confronted was how to make the wood stick to the material used to strenghten it. Starting in 1991, they undertook thousands of tests to find the best mix.
The beauty of composites, Dagher said, is that you can engineer them to have exactly the properties you want. In this case, to add strength, to adhere to wood and to not corrode or weaken when exposed to the elements.
Peter Lammert, a utilization and marketing forester with the Maine Forest Service, sees the project as a back-to-basics movement.
The first timber bridge, which was put in place in Gray in 1991, was made of Eastern hemlock which was harvested within 25 miles of the bridge. The wood was cut at a sawmill just a couple of miles away and laminated at the nearby Mechanic Falls plant.
Using local products and local labor is preferable to importing concrete and steel that is also more difficult and time consuming to repair, Lammert said.
The national recognition is also good news.
“Maine, being way up on the end hairs on the tail of the dog, tended to get only fleas and not much else,” Lammert said.
Now, the tail’s wagging the dog.