Architect 2014-07.pdf

95
HONORABLE
MENTION
SOM associate and
engineer Benton Johnson
estimates that a 42-story
timber tower would be 55
percent lighter and emit
78 percent less carbon
than its concrete-tube
constructed counterpart.
SKIDMORE, OWINGS & MERRILL BELIEVES THAT A HIGH-RISE MADE
OF ENGINEERED WOOD WOULD BE BETTER FOR THE ENVIRONMENT.
NOW THEY HAVE TO CONVINCE EVERYONE ELSE.
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
Floor System Model
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. Jonson 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.
Reinforced concrete
spandrel beam
Solid timber shear walls
Solid 8"-thick
floor panels
Reinforced linear concrete beams
Built-up timber
columns
Reinforced concrete
wall joint
Timber framing
within core
ARCHITECT JULY 2014 WWW.ARCHITECTMAGAZINE.COM