Belltown high-rise won't be imploded
If the McGuire Apartments high-rise in Belltown is indeed demolished next year, it couldn't be imploded like the Kingdome in 2000. Instead, each floor would need to be cut apart, their concrete slabs gingerly lowered by crane, from the top down.
Seattle Times staff reporter
If the McGuire Apartments high-rise in Belltown is indeed demolished next year, it couldn't be imploded like the Kingdome in 2000.
Instead, each floor would need to be cut apart, their concrete slabs gingerly lowered by crane, from the top down. By then, appliances would have been removed, windows dislodged, wiring yanked out, support steel carefully extracted. This wouldn't quite look like a reverse video of the 25-story building's erection in 2001, but a memorable scene nonetheless.
The project could employ 100 workers and take 12 to 15 months, said Dave Whitley, chief operating officer of Nuprecon, a leading demolition firm that considers itself a contender to raze the McGuire.
This would be the first high-rise in Seattle, and among the first in the nation, to be deconstructed under 21st-century conditions that add to the challenge.
Three modern challenges:
• The concrete floors are laced with about 5,000 steel reinforcing tendons, under high pressure. Cut them the wrong way, and pieces of the structure could become lethal projectiles.
• Belltown is a dense urban area with pedestrians, buildings and traffic only a few feet from the shell of the high-rise.
• Most of the material probably would be recycled.
Fewer than a handful of demolition firms are capable of tackling the McGuire, said Whitley.
The McGuire's owners announced last week that the building must be vacated this year, then demolished, because construction defects will gradually make it vulnerable to earthquake or deterioration. The final outcome is still under dispute — the high-rise's builders say that areas of corroded steel, woven horizontally through the concrete floors, could be fixed.
The building's agent, Kennedy Associates, is just beginning to explore a strategy for deconstruction. At least one other firm, NRC Environmental Services of Kent, considers itself a potential candidate for a McGuire demolition contract.
The company would try to resell or reuse appliances, such as ranges and dishwashers. Tenants have been chuckling at managers' request that they avoid moving-out parties that involve taking out their frustrations on the contents.
A number of local businesses, such as Earthwise and the REstore, resell building materials, fixtures, doors and molding. Sound Transit was able to save plants, faucets, even 13 claw-foot bathtubs when it razed buildings at its future Capitol Hill rail station. There ought to be valuable copper wiring inside the McGuire, said Saeed Daniali, professor of construction management at the University of Washington.
But the trim and fixtures are mainly "composites" rather than classic hardwood floors, metal wash basins, granite countertops and such, said 21st-floor tenants Sol De La Cruz and Gena Borriotti.
Still, about 80 percent of materials could be recycled or reused, said Daniali. About 50 percent of all demolition materials in the Seattle area are recycled.
Owners are generally not required to recycle a building, said Joel Benslaben, green-building specialist for Seattle Public Utilities. But it's often done, he said, because concrete costs around $75 a ton to recycle but $125 a ton to send to a landfill.
An intriguing question is whether about 1,000 windows would have a second life. Daniali thinks they could be marketed to another builder, but Whitley suspects the resale value is far less than the cost to preserve them.
Once the salvageable pieces were out, the tear-down could begin.
A spectacular implosion isn't possible because or problems with vibration, dust and debris, experts say. Instead, a variety of methods would be used.
Whitley said only very few buildings are ever imploded. He can't foresee using explosives at all in the McGuire. Once the shell was down to a five- to seven-story height, tall machines could knock down walls and floors, he said.
The most delicate task would be with high-pressure steel that was used to "post-tension" the concrete floors.
In post-tensioning, steel tendons are laced through a concrete beam or floor, then tightened like a rubber band. This compresses the concrete, adding strength and making cracks less likely. The steel bands also help the concrete floor support more weight, so less concrete is needed.
A spectacular example is the 2007 Tacoma Narrows Bridge, whose concrete struts were post-tensioned — to 56 million pounds across two of the three horizontal struts, adding seismic strength.
Typical high-rises require a mere 200,000 to 300,000 pounds per square inch, still enough to hang a semi-truck off the side of a building, said Ken Carper, a Washington State University professor and forensic engineer.
How serious a threat is this stored energy? In 1980, the roof of Congress Hall in Berlin suddenly broke apart and buried a man when steel tendons failed.
Before cutting apart the floors at the McGuire, engineers would need to devise an orderly sequence to loosen the steel tendons.
A healthy level of respect is called for to avoid a whiplash, Whitley said.
Post-tensioning was initially applied to bridges, but wasn't commonly used in high-rise buildings until the latter 20th century. Few have been deconstructed this way; among them is a Nuprecon project in Portland.
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org