North America is now at the forefront of blast testing, with research labs in the United States and Canada putting timber samples to the test.
Earlier this month, Wood Central revealed that the US Department of Defence and the State Department were “blast testing” mass timber construction systems amid growing interest from both departments to use cross-laminated timber in various building applications.
“Surprisingly, cross-laminated timber is pretty blast resistant,” according to Kevin Naranjo, the National Program Manager for Mass Timber at the US Forest Service Wood Innovations Program, who spoke to Wood Central about the future of timber construction in North America. “Blast testing will be a game-changer, not just for the military but for construction more generally.”
However, not to be outdone by their southern counterparts, Canadian researchers at the University of Northern British Columbia’s (UNBC) Innovation Research Lab are also busy learning how timber reacts under planned (and unplanned) blast scenarios.
That includes a day in August last year (August 22, to be precise) when the UNBC’s Wood Innovation Research Laboratory was in the wrong place at the wrong time (or perhaps the right place at the right time) – when the neighbouring Achillion Restaurant exploded.
The blast would later be blamed on people trying to steal copper that ruptured a natural gas line that was subsequently ignited by a cigarette lighter.
The ensuing fireball injured three people and shot burning debris at lightning speed into the west-facing side of the wood innovation building with enough force to pierce the wall of the research lab, causing it to burst into flames.
Despite the intensity of the explosion and heat from the fire, the state-of-the-art mass timber structure – built to airtight Passive House energy efficiency standards – bent but did not break, proving the flexibility and strength of the wood mechanics that went into its construction, the university reported.
“It’s pretty rare that you get to see a building that you designed to go through something as extreme as an explosion next door,” according to Adam Gerber, CEO/principal of Aspect Structural Engineers.
The building, beside the Wood Innovation and Design Centre, is used by UNBC students to test cutting-edge design advancements in wood construction technology.
How well it withstood the explosion from the triggered sprinkler system was an unplanned experiment that produced positive results.
“Overall, the building performed better than anyone could have predicted or expected based on the severity of the events that occurred,” he said.
The wall that bore the brunt of the massive pressure wave of an explosion strong enough to sway window curtains of suburban houses kilometres away in College Heights was torn away from the steel brackets that anchored it to the base of the building, leaving a two-inch gap at the bottom.
The self-supporting wall facing the blast was independent of the load-bearing post-and-beam main structure of the building, which was left undamaged.
The prefabricated exterior wall panels were strengthened by floor joists and filled with ground-up rock insulation, which acted as a barrier to the fire and did not burn.
Because of its modular prefabricated design, a Winton Global construction crew found it relatively easy to follow the original design plans to replace each of the panels burned in the fire and refinish the wall with its water vapour membrane and corrugated steel skin.
“A big part of Passive House is the energy standard, but it’s also the comfort of the occupants, and as we’ve discovered, it’s about resiliency and designing a building where the unexpected will happen,” said David Claus, UNBC’s director of facilities management and capital planning.
“Eventually, a wall will get wet, and when it gets wet, how will you ensure it dries itself and doesn’t sit there and rot or grow mould? In some ways, the building is self-healing, which I like.”
Located at 1153 Fourth Ave., the 1,070-square-metre Wood Innovation Research Lab opened in 2018 at a cost of $2 million. The damage to that building and contents attributed to the explosion was pegged at $1.3 million.
According to Mr Claus, most of that insurance claim was to replace the computerized load-bearing testing equipment that was flooded by the sprinkler head activated by the heat of the fire that got through a small section of the wall.
The lab is large enough to build a two-storey structure that can then be tested for earthquake resistance using hydraulic machines. The hydraulic pump, cylinders, and computer system suffered the brunt of the water damage.
“The sprinkler system caused most of the damage; the fire inside was pretty small,” said Mr Claus. “The sprinkler came on and put out the fire like it’s supposed to, and there was a bit of charring on a couple of pieces of wood. But the water (which ran for more than a full day) got some equipment wet, and unfortunately, some of the most expensive equipment was right where the fire came through.
“That’s the stuff we’ve been looking to restore; it’s pretty specialized equipment. We still don’t have the equipment back.”
Mr Claus said some of the WIRL’s contributions to wood construction research are included in the latest Canadian Wood Design Standards publication, which will be released later this year.
“A lot of the changes in this version are based on research done in this facility,” said Claus. “We’re helping to shape how buildings across Canada and potentially other parts of the world are designed.”
- To learn more about blast testing and how it could lead to greater use of mass timber in building projects, click on Wood Central’s exclusive interview with Kevin Naranjo from the US Forest Service Wood Innovation Program.
