How wood is making a comeback in construction

We have been using wood to build things for a very long time. According to recently discovered remains of a half-million-year-old wooden structure in Africa, we were building with wood before we were fully human. From these beginnings to the stave churches of Scandinavia to Lincoln’s log cabin, wood as a building material was favored for its abundance, workability, and beauty.

Yet over the past 150 years, as cities and skyscrapers boomed, wood was eclipsed by new materials such as concrete and steel. These materials can support more weight, allowing taller buildings to be constructed, and are not as susceptible to fires, earthquakes, and moisture damage. However, they cost more to produce, are non-renewable and have a heavy carbon footprint; steel and concrete production accounts for more than 10% of global emissions.

But talk to Chris Pantelides, an engineering professor at the University of Utah, and he’ll tell you we shouldn’t accept the domination of the steel and concrete jungle just yet. Thanks to the work of civil engineers like Pantelides, our oldest building material is experiencing a revival, even able to withstand earthquakes.

Wood represents both the past and the future of construction

Sitting in his office in the civil and environmental engineering department at the John and Marcia Price College of Engineering, he held up a block of composite wood about 12 inches long and 10 inches wide and smiled.

“What you’re looking at here is the future,” Pantelides said.

This deceptively simple piece of wood is an example of “mass timber” technology, a category of “engineered wood products” set to revolutionize the construction industry, which Pantelides has spent the last seven years to study and develop.

On the desk in front of him, among other pieces of wood and long metal dowels, was his latest research paper, titled “Design and Cyclic Experiments of a Mass Timber Frame with Reinforcement Retained by Wooden Buckling” , published in the Journal of Structural Engineering. It explores the best ways to build a buckling restrained brace (BRB), a type of building support that protects against seismic damage, with mass timber.

As a construction technique, mass timber is defined by the use of columns, beams and boards, made of several layers or pieces of wood tightly laminated or bonded together. The two types of mass timber that Pantelides works with are known as mass plywood and mass lamella, which have several advantages, environmental and structural, over typical building materials.

“The wood we’re talking about is very strong. It can replace steel or concrete in many building frames, but it’s much lighter,” Pantelides explained. “A mass timber building is also a quarter of the weight of a concrete building, requiring much smaller foundations.”

Thanks to its super-compressed composition, solid wood is effectively fire-retardant, resistant to moisture damage and very durable. With today’s sustainable forestry techniques, the use of wood is more sustainable and “renewable” than ever before.

Wood sequesters carbon while concrete emits it

“It only takes seven seconds for European forests to produce enough wood needed to build a three-bedroom apartment,” Pantelides said. “Canada alone has enough wood to house a billion people in perpetuity, with forest trees recovering faster than the population.”

Each ton of wood grown removes 1.8 tons of carbon dioxide from the atmosphere. A mass timber building could be 25% faster to construct than a concrete building and would result in 90% less construction traffic. Once the structure is completed, the wood goes from being a natural benefit to being a natural benefit.

“People just like to be in buildings with a lot of exposed wood,” Pantelides said. “The feeling of being connected to nature, biophilic design, creates healthier living and working environments.”

Thanks to its ability to bend and not break under pressure, steel remains the gold standard for high-rise buildings, especially in areas at high risk of earthquakes or hurricanes. Maintaining the structural integrity of a building relies on a thorough understanding of these properties, an understanding we don’t have with stiffer mass timber. This is where Pantelides’ research comes into play.

With its varied compositions, solid wood is far from being universal; the type of wood used, the size and shape of the wood particles, how they are glued together or even whether individual layers are stacked parallel or perpendicular to each other will greatly influence how the finished product reacts under constraint.

Since he began studying solid wood, Pantelides has troubleshooted and experimented with different “recipes”, finally arriving at one that involves shaving dark fir wood into shavings, compressing the shavings tightly together into boards or planks , then laminating these layers together with solid wood. ultra-strong glue. The resulting plywood can then be securely attached to other pieces of wood with joints made of steel dowels and plates.

Using this formula, Pantelides and his team experimented with mass timber versions of earthquake-resistant architectural elements, including the Timber Buckling Restraint Bracket (T-BRB), the focus of the most recent publication of Pantelides.

How to Make Solid Wood Resistant to Natural Disasters

In traditional architecture, wood-free BRBs absorb the seismic force of an earthquake away from the building frame and redirect it to a steel core inside the reinforcement, which is usually encased in a steel tube filled with concrete. Instead of the structural integrity of an entire building being threatened, only the supports will suffer significant damage and need to be replaced. Pantelides focused on developing a BRB which, while still using a steel strip for the core, is made from solid wood and suitable for solid wood frames.

This concentration requires specialized equipment. In one of the college’s hangar-style labs, in the Layton Building, a towering rectangular metal tower, an actuator, extends from the ceiling to below the concrete floor. This gigantic red contraption simulates the effects of seismic activity on anything placed inside by rocking it back and forth. This is where Pantelides and his team can test “lateral force resisting systems” (LFRS), like the T-BRB.

He and his graduate student Emily Williamson, co-author of the new paper, developed several different configurations of this T-BRB before inserting them individually into a wooden frame, which was then placed into the actuator. Then horizontal shaking, and lots of it, with forces equivalent to a magnitude 7.0 earthquake, for nine tests. Sensors attached to the T-BRB and frame recorded how different elements warped or moved as testing progressed.

Next, the frame and reinforcements were dismantled, inspected and measured. Pantelides’ study, co-authored by industry researchers Hans-Erik Blomgren of Timberland and Douglas Rammer of the Forest Products Laboratory, presents the resulting data, analyzed, graphed and compared between the different subsets. This information will help accelerate the use of solid wood, allowing it to become stronger and taller.

While mass timber construction has been used in Europe for several decades, the United States has been slower to adopt it, in part because strict building codes focused on steel and concrete, treating with caution any use of wood to construct tall buildings.

But today, thanks to recent changes to these codes, as well as research into components such as Pantelides’ T-BRB, mass timber is expected to proliferate even in disaster-prone areas, meeting growing demand more sustainable building materials. The most recent version of the International Building Code, the central body of building regulations in the United States, included a construction type for buildings up to 18 stories. A record-breaking 25-story hybrid mass-timber-concrete building has been built in Wisconsin, and Utah has a five-story building under construction in Draper.

“The whole world is waking up. People are going to look back and say, ‘Hey, why didn’t we build this with mass timber?'” he said. “I think in the next 20 years there won’t be many buildings under 12 stories, or even 18 stories, built of steel and concrete. It’s just not going to be feasible anymore. In the near future, we We will even see skyscrapers, more than 50 stories high, built from solid wood.