| 340 on the Park|
Condo's Structural Design Could Help Cement Buyers
The downtown Chicago condominium market is among
the hottest in the nation, with abundant choices for buyers.
Gail Lissner, vice president of Chicago-based Appraisal Research
Counselors, said about 4,700 units are expected to be delivered in the Loop in
2006, up more than 50 percent from 2005's 3,100 units.
The structural design
of the $250 million 340 on the Park condominium in Chicago's East Loop might help
give the building sales advantages.
The building with curtain-wall cladding
will have striking views. Overlooking Randolph Street, 340 on the Park is immediately
north of Daley Bicentennial Plaza, northeast of the nationally famous Millennium
Park and west of Lake Shore Drive. In addition to those, the 69-story high-rise
will have vistas of Grant Park, Lake Michigan and the landmarked Michigan Avenue
The building had reached the 39th level in early May. Top-out
is expected in October, and the project should be finished the following October.
concrete structure features post-tensioning, said Ola Johansson, project manager
for Seattle-based Magnusson Klemencic Associates, the structural engineer.
key benefit of post-tensioning is improved floor-to-ceiling height due to thinner
but equally strong slabs over a conventional structure with "mild-steel"
slabs - not a small consideration for a developer in the Loop's superhot condominium
market. The floor-to-ceiling height in 340 is 9 ft. but would have been between
8 ft., 8 in. and 8 ft., 10 in. with a conventional system.
a potential buyer would compare with another building," Johansson added.
the column-to-column span in 340 on the Park is 27 ft., Johansson said. If the
building had been constructed with an 8-in.-thick mild steel slab, the column-to-column
span would have ranged between 22 and 25 ft.
The wide span is mimicked
in the building's first six levels where the parking is located, though those
levels have mild steel slabs. The 10-in.-thick floor slab is strong enough to
accommodate the wide span, whereas an 8-in.-thick floor slab in the tower has
sufficient strength because of the post-tensioning.
As a result, the building's
deeded 471 parking spaces are greater than would have otherwise been the case
if post-tensioning had not been used above.
"So the additional parking
stalls we were able to eke out with the post-tensioning system offset any construction
premium to install the post-tensioning," said Ron
of Magnusson Klemencic.
Klemencic, who is the immediate past chairman and
still a board member of the Council on Tall Buildings and Urban Habitat, an international
association of architects and engineers headquartered in Chicago, added that the
building is possibly the world's tallest post-tensioned concrete building and
definitely Chicago's tallest such structure.
"I believe this is going
to be the tallest post-tensioned concrete building in North America," he
said. "If there is a taller one, I don't know what it is."
The post-tensioning process involves hydraulically tensioning
each concrete floor slab.
Steel tendons that are anchored to posts and
sheathed in green plastic are laid in the metal deck, and the concrete is poured,
Brandt said. After the concrete has hardened, the cables are stressed hydraulically.
than one cable band is involved per floor, and the number of tendons per floor
ranges between 100 and 1,000.
A key issue is coordinating the layout of
the cables and the lines for the electrical, plumbing and other utility systems.
Sometimes, a conflict can arise between the two.
cabling has to go where it has to go to allow the building to act as it needs
to for structural reasons," Brandt said. "At the same time, plumbing
piping has to go where it has to go to service a bathroom or kitchen."
a conflict arises, every party involved is assembled to find a solution, and conflicts
between post-tensioning and utility lines arise "quite a bit," Brandt
said. A cable could be swept in a new direction to accommodate a utility line
or a utility line redirected.
Typically, the post-tensioning cable gets
priority over utility lines "to allow the building to stand up at the end
of the day," Brandt said. In some cases, however, the post-tensioning cables
are moved and extra reinforcing steel is added in that area for stiffness. Cost-effectiveness
and owner's requirements are considered in making the decision.
have been post-tensioned in Midwest before, but Klemencic said the process is
more common on the West Coast and Southeast partly because of building tradition.
a result, crews on the 340 project were a little apprehensive about the process
because they wanted to maintain a three-day pour cycle per floor.
the beginning, they were talking about maybe four or even five days per floor,
but they've been executing it three days per floor," Klemencic said. That
means the project is ahead of schedule.
The project is on a previously unused lot between the Blue Cross Blue Shield
office on the west and The Buckingham condominium on the east.
Only a half-story
is below grade in landfilled area, and the first six levels will hold the parking
and face Lower Lower and Lower Randolph Street. The first condominium level is
two floors above Upper Randolph Street - or the eighth level overall.
975,000-sq.-ft. building will hold 344 condominium units that range between about
1,000 and 5,000 sq. ft. in one-, two- and three-bedroom layouts, said Don Biernacki,
senior vice president of Chicago-based LR Development Co., the developer. Customizable
penthouse units start on level 57.
Neither the percentage of units sold
nor unit costs was released.
About 4,000 sq. ft. of space on the seventh
floor, which is flush with Upper Randolph Street, will hold retail. The building
will feature an amenity floor on the 25th level, including a pool and fitness
A "signature" building was sought, so a quality aesthetic
design and finishes were needed, Biernacki said.
Rather than just only
curtain wall, the exterior features variation with protruding and inset balconies
and horizontal and vertical lines. Inside, bamboo - a sustainable material - is
used for the typical unit flooring, and there will be high-end cabinets, faucets
and other items.
Lower, Lower Randolph
The maze of streets beneath Chicago's normal level
can be confusing for those drives not used to navigating the city's lower depths. Numerous obstructions
were encountered on the project, including a "forest of wood pilings"
probably used as retaining walls decades ago when Lake Michigan's shoreline was
west of its present location, Brandt said. Old boat docks and haul roads were
issue on the $250 million 340 on the Park condominium project was the access point
on Lower Lower Randolph Street.
Materials are coming from points all over
the country, and "the lower roads are difficult to explain to someone on
how to get there," said Bert Brandt, senior project in Chicago with Bovis
Lend Lease Inc., the general contractor.
MapQuest, the popular Internet
site often used for navigation, would prove useless if trying to map a route to
the lower depths of Randolph because it does not include the below normal grade
"More than a couple times" a delivery was expected but
went missing, and someone was dispatched to find the driver on the streets of
downtown Chicago, Brandt said.
Other times, deliveries meant for other
projects, such as those in the nearby Lakeshore East development, came into 340's
lot, he added.
As a result, drivers are instructed to call the field office
before making a delivery, and specific directions are given.
But the site
below the city's normal grade proved an advantage when it came to constructing
The large amount of space on grade has allowed large flying forms,
rather than stick-built forms, to be used on the project. A spillover benefit
is that flying forms allow the teams to maintain their three-day pour cycle.
Chicago, you don't see flying forms often because you're in boxed-in sites,"
Other issues arose on the project:
Backhoes were used to demolish most obstructions.
But some impediments, such as old retaining walls, were extracted with a chain.
Because of the project's closeness to the lake, groundwater infiltrated the site.
Water wells were drilled and pumped.
About 75 percent of construction
waste has been sorted because a goal to achieve Leadership in Energy and Environmental
Design certification. Also as part of certification, a percentage of materials
has been obtained from within 500 mi. of the site.
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