Bending, not breaking: Engineered wood products help rebuild Christchurch

 IUFRO Plenary 1: Modern Timber Buildings from Sustainable Forests

Andy Buchanan presents the first plenary session at the IUFRO World Congress.
Andy Buchanan presents the first plenary session at the IUFRO World Congress.

 

Just a few years ago, two major earthquakes struck Christchurch, New Zealand within six months. The first, a 7.1-magnitude quake, struck the Canterbury Plains to the west of the city in September 2010, but resulted in no deaths. The second, a 6.3-magnitude aftershock from the first earthquake, took place under downtown Christchurch in February 2011 and resulted in 182 deaths and extensive damage to commercial buildings and houses.

Because most of the buildings in Christchurch were constructed of steel and reinforced concrete, two materials that don’t stand up well to earthquakes, they could not be repaired. Instead, it was cheaper to demolish them and rebuild from the ground up.

This also presented an opportunity to reshape the future face of Christchurch, according to Andy Buchanan, who delivered the first plenary at the 2014 IUFRO World Congress.

 “What kind of city do we want?” he asked. “Why can’t we use wood to rebuild?”

In particular, Buchanan discussed using engineered wood products such as laminated veneer lumber (LVL) and cross-laminated timber (CLT), which unlike solid lumber are made of wood particles, veneer, or fibers held together with adhesive.

Using engineered wood to construct buildings has many benefits. The material is a renewable resource, can be carbon negative, is relatively lightweight, and is aesthetically pleasing.

Perhaps of most importance to the residents of Christchurch, however, is the fact that buildings made of engineered wood hold up better under earthquakes than structures built of steel and concrete. Engineered wood buildings can actually absorb energy from an earthquake and then return to form.

In other words, they bend but they don’t break.

In addition to providing a safer construction material for earthquake-prone areas, developing markets for engineered wood either domestically or as an export would make solid economic sense.

According to Buchanan, who earned a PhD in wood engineering from the University of British Columbia, forestry in New Zealand is heavily based on the cultivation of radiata pine. Approximately half the radiate pine harvested is exported as logs. More use or radiata pine in LVL and CLT for engineered wood products could transform it into a top-class engineering material.

The shift to engineered wood products and away from concrete and steel as construction material is not without challenges. Obstacles to more use of engineered wood in multi-story buildings include an entrenched building construction industry which would prefer to stick with “tried-and-true” steel and concrete structures instead of trying something new, as well as a strong political lobby supporting steel and concrete industries. Public perceptions about fire safety, durability, noise, and thermal insulation also factor into the slow adoption of engineered wood in the construction of tall commercial buildings.

Currently, according to Buchanan, wood represents approximately 10 percent of the construction market in New Zealand, where, because of the low cost, imported steel still dominates. The concept of tall wood buildings is new and will take time to gain wide acceptance. The long supply chain from the forest to the builder means that you have to convince everyone involved along the way that engineered wood is a preferable construction material. 

“If there’s just one person along that supply chain who says, ‘I’m a bit nervous about this,’ it won’t happen,” he said. “But the price goes down the more you manufacture something. As more are built, the price will drop and engineered wood buildings will gain in popularity.”

Despite the current higher cost of engineered wood products, using wood as a construction material for multi-story buildings is gaining traction around the world. Builders in Norway are currently planning a 20-story timber building, while others in Canada are planning a 30-story building. In the United States, plans are underway to design a 42-story building built of engineered wood in Chicago.

Because wider acceptance of engineered wood could use a bit of an economic kickstart, the Canadian government contributed funding to help design timber buildings in Ottawa, Quebec City, and Vancouver. In the United States, the U.S. Department of Agriculture and the U.S. Forest Service are promoting a prize competition for constructing a tall building out of engineered wood.

Buchanan concluded with an optimistic note. “The more trees we plant and grow and harvest and use for sustainable buildings, the better it is for our health and our wealth and for a sustainable planet.”

Read more about Andy Buchanan and his “seismic design” work with Christchurch.

Written by: Peter Gomben, U.S. Forest Service

blog comments powered by Disqus