In a world where reinforced concrete and steel-framed buildings dominate in commercial construction, a timber tower may sound like an architectural oddity. But to Skidmore, Owings & Merrill (SOM), it represents a new type of high-rise that has a 60 to 75 percent smaller embodied carbon footprint than conventional structures. The Timber Tower Research Project, spearheaded by associate and engineer Benton Johnson, lays out a preliminary structural design of a hypothetical 42-story tower built of mass timber columns and panels alongside reinforced concrete wall joints, spandrel beams, and link beams. “It’s an engineering tour de force,” juror Bill Kreysler said. “With wood, you can select shapes that are optimized for the structure.”
Johnson contends that manufactured timber products such as cross-laminated timber (CLT) and glued laminated timber (glulam) are roughly as strong as reinforced concrete, provided that the timber is loaded correctly and used in conjunction with concrete or steel joints. “Wood is strongest when it’s loaded in compression, parallel to the grain,” he says.
The payoff is that timber is a more sustainable building material than the alternatives. It absorbs carbon while growing, takes significantly less energy to manufacture than concrete or steel, and it can be responsibly harvested and replenished. To underscore the point, Johnson modeled and estimated that the hypothetical timber tower would be 55 percent lighter and emit 78 percent less carbon than a comparable 42-story, conventionally constructed tower modeled after Chicago’s Dewitt Chestnut Apartments, also designed by SOM. Now called the Plaza on Dewitt, the concrete-tube structure was a benchmark of efficient construction at its 1965 completion.
Juror Mimi Love said the Timber Tower Research Project was a “strong proposal based on sustainable performance.” But, like the other jurors, she felt that the submission needed to address the crucial issue of fire safety and building codes. Johnson acknowledges that he is no fire engineer, but he believes that a timber tower could be designed to be sufficiently fire resistant. When exposed to fire, timber, unlike wood, chars on its surface and forms an insulating layer around the core material, retaining some structural integrity. In other words, he says, the timber structure wouldn’t even need an applied coat of fireproofing.
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Project Timber Tower Research Project
Design Firm Skidmore, Owings & Merrill
Primary Investigator Benton Johnson
Project Team Richard Tomlinson, FAIA, William Baker, David Horos, Joshua Schultz, Kevin Rodenkirch, AIA, Andrés Montaña, AIA, and My-Nga Lam, AIA
Client and Funding Softwood Lumber Board
Special Thanks Anthony Forest Products; American Wood Council; FPInnovations; Idaho Forest Group; Structurlam Products; Shen Milsom & Wilke; University of Queensland; WoodWorks; and Dr. Nick Isyumov