MEDIA INFORMATION

Improving on Nature: The Environmental and Performance Merits of Engineered Wood

by Jim Petersen

Engineered wood is the future.
- Dr. Bruce Hoadley, University of Massachusetts, Amherst, “This Most Magical of Natural Fibers,” Evergreen, Summer, 1993

The whole design of a tree limb employs the yin and yang of good engineering - tension and compression, or pull and push. This allows saplings to become vertical again after being buried by snow. (When wind blows on a tree, the windward side of the tree is in tension and the leeward side is in compression.) In broad-leaved trees, the upper side of a limb normally grows faster than the lower side, and the cells on the upper side shrink longitudinally. When a branch bends under a load of snow, the cells on the tree limb’s upper side shrink to allow for recovery.
- Delta Willis, “Naturally Inspired,” Natural History, February, 1996

In 1850 the English architect, Joseph Paxton, designed what was surely the most impressive building of its era. Perhaps of any era. It was called The Crystal Palace, and was built to house showpieces of Victorian technology.

The structure was 1,848 feet long and 408 feet wide. Its superstructure supported 293,655 panes of glass. Hence its name.

More than six million people—roughly one-third of the entire population of the United Kingdom--strolled beneath the Palace’s glass ceiling. No doubt British historian Thomas Macaulay spoke for all of his countrymen when he called Paxton’s Palace “a most gorgeous site; vast; graceful; beyond the dreams of the Arabian romances.”

But Macaulay failed to note one important detail about the Palace. Its most awe inspiring feature—a great glass dome that stretched the length of the building—was framed in wood. Perhaps he did not notice because Paxton had wisely ordered the wood superstructure painted to look like steel. Otherwise, the public would never have entered the Palace, fearing its collapse. But Paxton knew the truth about wood’s enormous strength, and was willing to risk his reputation on its structural integrity.

The magazine, Natural History, attributed Paxton’s daring to his discovery of “a simple yet elegant design canon, discovered by plants millions of years ago - the principle of minimum weight. Because every material used to stiffen or support a structure also adds to the total load the structure must bear, adding height unavoidably means trading off between a material’s strength and its weight.”

What Paxton knew was that, pound for pound, wood is stronger than steel because it has a more favorable strength-to-weight ratio.

The secret to wood’s enormous strength lies in cellulose, the basic ingredient in all plant cell walls. You can’t see this cellular structure with the naked eye, but it is stiffer and stronger than nylon, silk, chitin, collagen, tendon or bone - a fact that goes a long way toward explaining why the largest living organisms are trees, and why wood is a near perfect building material.

Lorna Gibson, a professor of engineering at Massachusetts Institute of Technology, attributes wood’s mechanical efficiency to its unique-in-nature combination of composite and cellular structure.

“Wood’s exceptional performance in bending reflects the fact that the trunk and branches of tree are often loaded in bending; the trunk by the wind and the branches by their own weight. It arises from the honeycomb-like structure of the wood cells as well as the great stiffness and strength of the cellulose fibers.”

James Gordon, a leading biomimetrician and retired materials science professor at England’s University of Reading, calls cellulose “a tensile material without peer.” (Biomimetricians study successful patterns in nature, looking for ways to improve the design of everyday products. Increasingly, their attention is focused on how trees overcome stress. Recently Claus Mattheck, a German physicist, redesigned the threads on a spinal screw to mimic the way a tree limb is reinforced by the trunk. Elsewhere, biomimetics has been used to improve the designs of artificial joints, electric razors, automobile parts and washing machines.)

Few have spoken more eloquently about wood’s amazing mechanical properties than Dr. Bruce Hoadley, a long-time wood technology professor at the University of Massachusetts, Amherst campus.

“Think about this for a moment,” Dr. Hoadley declared in a 1993 Evergreen Magazine interview. “Here we have this natural material, created by nature out of free solar energy, water and carbon dioxide. Put this stuff under a microscope and you see millions of wood cells joined together in ways that allow them to transfer and share load-bearing stresses. As trees, these cellular structures engineered in nature make perfect columns and beams. And what are the roof, wall and floor systems found in houses? They are systems of columns and beams. This is why wood is an ideal building material, and it is why engineered wood is the future.”

Over the last 15 years, engineering technology has changed the forest products industry in ways unimagined 25 years ago, altering not only the way wood products are made, but the products themselves. The implications are profound, for builders, for consumers, and most certainly for those who are trying to shape the nation’s forest policy.

Engineered wood is not new. One of the first such products—plywood—was introduced nearly a century ago, and gained wide acceptance during the post-World War II housing boom. It revolutionized the way homes are constructed, all but eliminating tongue-and-groove boards traditionally used as flooring, sheathing and roofing material.

But the real story behind plywood’s half-century of success is still not well understood. Plywood manufacturing technology—the manner in which thin layers of wood were cut from logs—increased log recovery by about 50 percent. In so doing, this new technology stretched the fiber supply without increasing manufacturing cost. In fact, competition between manufacturers drove costs down, which put more, lower cost plywood in the hands of post-war homebuyers.

But plywood manufacturing technology did something else for which it has never received due credit. Because more wood could be recovered from each log, fewer logs were needed to meet soaring demand, which meant less harvesting than would otherwise have been necessary to satisfy the nation’s seemingly insatiable appetite for wood. Older Americans will recognize this act, and call it by its real name: conservation.

The basic technology used in early plywood manufacturing remains the same: long, razor-sharp knives peel the log from the outside to its core—the peeling occurring as the log rotated on a fast-moving spindle. Today, though, computers are added to the process. Linked to laser-guided scanners, they calculate the best way to peel the log for maximum wood fiber recovery. Less wood is wasted, and more goes into the finished product, benefiting both consumers and manufacturers.

The technological revolution that began with plywood has soared to new heights, thanks in large measure to huge investments by the nation’s forest products manufacturers. Where once there was only plywood, there are now four families of structural engineered wood products: structural wood panels, including oriented strand board (OSB), structural composite panels and plywood itself; glued laminated timbers, often called glulam; structural composite lumber, including laminated veneer lumber (LVL), parallel strand lumber (PSL), and oriented strand lumber (OSL); and prefabricated wood I-joists, or I-beams, which require 50 percent less wood than is needed to make a solid wood beam of the same strength.

Most of these products define themselves. For example, oriented strand lumber is made from flaked strands of wood laid in directions (oriented) that maximize strength. OSL is assembled in large mats or “billets” that can then be cut into many different dimensions, depending on use. Common uses include wall studs, beams, joists, and door and window frames.

Laminated veneer lumber (LVL) and parallel strand lumber (PSL) also define themselves by their names. PSL is made from long veneer strands laid in parallel, then glued to form beams. LVL, which is widely used as lumber, is made by bonding thin wood veneers with the grain of all veneers running parallel. LVL can be assembled in billets 6-foot wide and 60-feet long before sawing begins. Imagine an old-growth timber of the same dimension, only stronger and more uniform. Now imagine sawing this timber into beams, headers, rafters, or planking. And the scraps that are left over will be fashioned into beautiful wooden salad bowls.

While each of these product lines is a technological marvel in its own right, their collective impact has had as much to do with their effect on forests and forest communities as it has had on improved structural integrity. Perhaps most significant is the fact this new generation of technology has made it possible for many western manufacturers to make a transition from years of dependence on federally-owned old growth timber now generally off-limits to harvesting. Structural timbers and large dimension lumber, which could only be manufactured from large, old trees, have given way to engineered products made from smaller, faster growing second and third growth wood grown on industrial and family-owned tree farms. An enormous amount of this same type of wood can also be found in diseased timber stands in the West’s national forests, but since 1990 more of it has burned up in wildfires than has been harvested, a result of environmental industry litigation aimed at blocking salvage logging, which many scientists believe is an essential first step in the process of restarting ecological processes long dormant in western national forests.

Though federal harvest levels have declined by more than 80 percent since 1990, the emergence of new engineered wood manufacturing processes has also saved thousands of jobs that would otherwise have been lost in the wake of the closure of more than 100 old growth-dependent lumber and plywood manufacturing plants.

Early fears engineered wood was structurally inferior to products cut from old growth timber have given way to the realization that even greater strength can be “engineered” or built into wood products by mimicking or replicating structural properties inherent in wood. Here, a deceptively simple explanation masks an incredibly complex engineering feat many years and millions of dollars in the making: By bonding or gluing together wood strands, strips of veneer, pieces of lumber or chips of wood, larger pieces of wood are created that are stronger than their parts.

Some examples: laminated veneer lumber is stronger in bending strength than traditional lumber of equivalent size by a factor of two or more. Thus, a given thickness of LVL can either span greater distances for the same load, or the same load can be carried with smaller sections of LVL. Glulam beams and wood I-joists can carry greater loads over longer spans than is possible with solid sawn wood of the same relative size. And oriented strand board and cross-laminated plywood distribute the loads they carry in all directions, while lumber distributes its load in only two directions.

In a word, performance.

“If you are an architect, engineer, building material specifier or building contractor, product performance is of paramount importance,” says Thomas Williamson, executive vice president of Engineered Wood Systems, APA’s nonprofit corporation. “Engineered wood products have set new, higher performance standards by minimizing both resource and manufacturing defects while enhancing structural integrity.”

Leonard Guss, a Woodinville, Washington engineering consultant described the performance advantages of engineered wood in an article published in the Forest Products Journal.

“In engineered wood, the range of performance is much narrower,” he wrote. “Our expectations of performance are much more likely to be realized. This is because the very process of making engineered wood products homogenizes the raw material, eliminating defects and weak points, or at least spreading and mitigating their impact.”

Apart from more predictable performance, there lies the matter of more predictable cost, a fact both Mr. Williamson and Mr. Guss attribute to advantages engineered wood products hold over their more traditional counterparts.

“Dimension softwood lumber is manufactured and sold only in two-foot increments,” Mr. Guss explains. “If a piece needed is one inch over the two-foot increment, 23 inches is discarded. (But) LVL can be purchased in one-inch increments, or less. There is no job-site cutting and no consequent waste that is expensive to buy and expensive to dispose of.”

Wood I-joists hold a similar advantage over lumber joists which have been a staple in the floor framing business for years.

“The logic in wood I-joists is impeccable,” writes Mr. Guss. “Long and wide dimension lumber, expensive and difficult or impossible to get, is replaced by inexpensive commodities: 2 by 4 or 2 by 3 lumber or LVL for the flanges, OSB or plywood for the webs. The result is a replacement product that performs much better than dimension lumber. Total costs are comparable because fewer wood I-joists are needed compared to dimension lumber, and call-backs due to complaints about squeaky floors are considerably decreased.”

Mr. Williamson adds yet another cost-related advantage, one with implications that seem certain to reverberate through the entire forest products industry.

“Engineered wood products can be made from a variety of wood species and grades,” he explains. “As a result manufacturers aren’t dependent on one or two species or grades. They can use whatever is most abundant, mixing both species and grade, and still produce a superior structural material. Thus, builders are less vulnerable to price volatility caused by environmentalist litigation and declining federal harvest levels.”

How this fact ultimately will reshape the nation’s wood manufacturing complex is difficult to predict, but it is worth remembering that engineered wood products can now be made by mixing western softwood species, including Douglas-fir, hemlock, ponderosa pine or spruce, with eastern hardwoods, like aspen or yellow poplar; or by mixing eastern hardwoods with southern pine.

One thing seems certain. Thanks to engineered wood technology, there will be less pressure to harvest large old trees the public reveres, and there will be markets for undersized dead and dying trees that crowd national forests, endangering both wildlife habitat and old forests the public wants preserved. Heretofore, few manufacturers have wanted to buy these trees, in part because the technology needed to turn them into finished products did not exist. Now it does. Now it is possible to rescue sick forests and their timber-starved communities, all in one motion. But Congress must gather the political will needed to tackle the forest health problem head-on.

There are also some profound sociological implications tucked away somewhere in this still unfolding story. Because engineered wood products are made from many different tree species that can be grown in controlled, plantation settings—and harvested earlier than wood grown in the wilds—look for the price of wood to decline in years to come. As it does, home ownership is going to fall within reach of more people. Forestry and technology will have made yet another priceless contribution to the American experience.

Meanwhile, thanks to advancements in both forestry and wood manufacturing technology, the nation’s timber industry is moving forward, proving the doomsayers and weepers and wailers wrong again.

Indeed, engineered wood is used today in scores of construction and industrial applications: in floor, wall and roof assemblies, as flooring and siding, as furniture framing and in boat construction, as concrete forming and scaffolding material, and in pallets, crates, bins and shipping containers.

Among the more spectacular applications of engineered wood technology: the Tacoma Dome, where a glulam framing system spans 530 feet, the Kibbe Dome at the University of Idaho, which uses laminated veneer lumber to span the school’s indoor football arena; and the glulam beam-engineered wood truss superstructure that bridges the protective cover on a 15-acre water reservoir in Los Angeles.

Certainly less exciting but no less important is the increased use of engineered wood in the federal government’s bridge replacement program. According to an inspection by the Federal Highway Administration, nearly 250,000 or the nation’s 600,000 short span bridges need replacing. “Timber used in today’s bridges is different from the materials with which many engineers are familiar,” Dr. Hota GangaRao, a University of West Virginia engineering researcher has noted. “New assembly methods, timber products or components made with glues, and preservative treatments, have made timber a feasible alternative to steel or concrete.”

Apart from clear technological advantages held by engineered wood products, there lies the fact that wood products hold inherent environmental advantages over their non-renewable competitors, including concrete, aluminum, steel and plastic.

Chief among these advantages is the fact that far less carbon dioxide producing fossil fuel is consumed in the manufacture and use of wood products than is consumed in the manufacture and use of comparable products manufactured from non-renewable natural resources. One scientific study compared the amount of energy required to build 10x100-foot walls constructed from wood and steel. The results were startling:

• The wood wall required 25 percent less raw material than the steel wall.
• In the extraction, manufacturing and construction stages, the steel wall required three times as much energy.
• Carbon dioxide emissions, which contribute to global warming, were also three times as great for the steel wall.
• Emissions of sulfur dioxide, methane, and nitrous oxide were also higher for the steel wall.
• Perhaps most revealing of all, it took 25 times more water to manufacture the steel wall than was needed for the wood wall, greatly increasing the risk of water pollution.

Forest products manufacturers have finally begun to capitalize on wood’s inherent environmental properties, and the strategy is producing the desired result, especially among consumers who fret about the environmental impacts of their buying decisions. The fact that wood is an environmentally friendly product is undeniably important to an increasing number of consumers, especially those living in politically powerful urban centers far removed from forests they love. Here, where technology is commonplace and forest conservation and recycling are near-religions, there is a growing appreciation for what engineered wood is doing for people and forests alike, which brings us full circle, to a natural law that is fundamental to engineered wood technology.

“Trees are smart,” says Claus Mattheck, inventor of the re-designed spinal screw that borrows its strength from the intersection of a tree limb with its trunk. “They grow wood in a load-adapted way; they use the strongest wood where the highest internal stresses are. They also optimize their external shape.”

So it is with engineered wood products. In both form and function, the objective is to use wood fiber in ways that replicate the strength and integrity of the original design: a tree standing in a forest.

Jim Petersen is executive director of the Evergreen Foundation and editor of its Evergreen Magazine. He can be reached via the Foundation’s website at www.evergreenmagazine.com.