Undergraduates explore use of mass timber

Students nervously pace the second-floor knuckle of Richardson Hall on a cool, spring day. Some flit to the walls to make sure their posters are perfectly secured and their models are ready to shine. Others nervously nibble on chips and watermelon.

It’s final exam time, and for students in assistant professor Mariapaola Riggio’s class, that means making a presentation in front of their classmates, other faculty members and industry professionals.

The class, Timber Tectonics in the Digital Age, examines how the design and construction of timber structural systems benefit from digital techniques. Architecture students from the University of Oregon’s School of Design are invited to enroll alongside Oregon State students studying renewable materials, wood science, civil engineering and construction engineering management.  All students work collaboratively, as part of a small team, thinking critically about how digital tools might be able to change the wood construction sector.

For their final project, the students were tasked with creating a ‘wood products pavilion’ that might represent the TallWood Design Institute at the International Mass Timber Conference in Portland in 2019. The institute is one of the nation’s top research collaboratives focusing exclusively on the advancement of advanced wood products. The students used parametric techniques to design adjustable forms, and then refined them according to structural analysis information. The final challenge has been to plan the construction process appropriate materials and detailing.

“We’ve had a great partnership,” says Nancy Yen-Wen Cheng, Architecture Department head at the University of Oregon. “And it has been a privilege to co-teach with [Riggio]. She brings knowledge of the latest advances in timber structures and has been insightful about how to employ my digital design specialization.”

Brent Stuntzner of CB Two Architects in Salem agrees. He served as one of the judges of the students’ final projects.

“I’m always really excited to go in and ask the students questions,” Stuntzner says.

Despite their nervousness, the students prevailed and presented thorough and exciting final projects.

“They are full of creative ideas,” says Stuntzner. “And after this class they are prepared to go into a variety of different environments within the construction and wood products industries.”

Putting CLT through the fire

“There’s a dirty little secret about wood,” says TallWood Design Institute researcher Lech Muszynski. “It burns.”

Muszynski studies the fire resistance of cross-laminated timber. When discussing this topic, he often refers to a photo from the great San Francisco fire in 1906. In the photo, two melted steel beams lay across a wooden beam.

The beam burned, while the steel softened. But Muszynski says the old photo proves the difference between flammability and fire safety.

“Materials that do not burn may be less fire safe than wood that does burn, but keeps its load bearing capacity much better,” he says. “In this case, the steel lost its load bearing capacity, while the wood, which didn’t burn completely, retains its ability to bear a load and saves the space below from being crushed.”

Despite this evidence from the early 1900s and recent research conducted in Europe, the American public is still concerned about fire when it comes to wooden buildings, and American construction companies don’t have enough data to ensure tall wooden buildings are up to code. Muszynski hopes to provide this data and put minds at ease with his latest research project, which tests the fire resistance of cross-laminated timber floors and walls.

“The point of my project is not to generate new science, but to provide a large-scale demonstration of how cross-laminated timber panels react to fire,” Muszynski says.

When Muszynski says “large scale,” he means it. Many of the panels he tested in a large furnace at the Western Fire Center in Kelso, Washington were too large to be transported in one piece, and had to be assembled on site.

The samples went into the furnace completely unprotected with any kind of fire-proofing materials typically used in wooden construction. Thermocouples, which measure temperature, were attached to the panels to collect data while the panels were exposed to fire.

Muszynski said that each panel experienced similar, gradual and predictable charring rates: the surface of the panels darkened within two minutes, caught fire and eventually a layer of char formed on the surface of the wood.

“Every floor panel we tested survived two hours of fire exposure,” Muszynski says. “After two hours we cut it off and inspected the sample. Only one wall sample failed after 90 minutes, and that’s still pretty good.”

The next step of the project is evaluating the charred samples. For this, Muszynski employed two Oregon State undergraduates.

“At first he tried to talk me out of the job,” says senior forestry student Cassie Holloway. “We were starting in the middle of summer, and doing this kind of heavy manual labor in the heat is pretty difficult.”

But Holloway and her partner prevailed. They cut each sample into one-foot by one-foot samples and evaluated the char depth to ensure consistency with data from the thermocouples.

Holloway first heard about CLT in her junior seminar class and was immediately intrigued.

“Growing up, I was very interested in conservation and sustainability,” Hollway says. “I think it’s awesome that people are using renewable materials to build up instead of out. I was really excited to be able to work on this project.”

Once sampling is completed, Muszynski says he will work to create a map of the char depth of each sample. Next, he hopes to test the fire resistance of connections used in CLT construction.

“Our ultimate goal is to make the TallWood Design Institute the one-stop place for testing anything mass-timber including CLT and glulam and whatever comes next,” Muszynski says. “This must include fire testing.”