Mass-timber-frame enthusiasts extoll the virtues of the structural material not only because it is renewable but also because building with timber is typically speedier, safer, simpler and quieter than building with concrete or steel. Still, most timber experts say hybrid structural systems are their choice for tall mass-timber frames because they take advantage of the best features of timber in combination with steel and concrete.
For the University of British Columbia’s 174-ft-tall Brock Commons dormitory—which, when it opens in September, will rank as the world’s tallest timber frame—the design team developed a hybrid approach for gravity and lateral loads, said Thomas Tannert, a University of Northern British Columbia professor of integrated wood engineering, at the 2017 Structures Congress, held in Denver on April 6-9. There were 1,377 attendees at the conference, hosted by the American Society of Civil Engineers’ Structural Engineering Institute.
The 18-story Brock building, sited in a seismic zone, consists of a one-story concrete base topped by 17 floors of mass-timber framing around a structural-concrete shear-wall core. Cross-laminated timber (CLT) floor panels, with a concrete topping slab only for acoustical insulation, span from the core to the glue-laminated-timber (GLT) column lines, creating 14-ft x 10-ft bays.
“There are no structural beams,” Paul Fast, founding partner of the project’s engineer, Fast + Epp Structural Engineers, tells ENR. “The [beamless] post-and-panel system is the key to the price point and the success of the system.”
Fast notes that CLT’s advantages include accuracy of member sizes—thanks to computer-controlled fabrication—and ease of construction. A crew can simply drop a panel, with an embedded steel connector, onto a steel stud that protrudes from the column. “You don’t even need carpenters to erect the timber elements,” says Fast.