Project
in Magnificent Mile
Two-in-One Building Holds Hotel, Parking
by Elaine Schmidt
Carefully phased concrete pours, an unusual crane placement
and a monorail system for hanging precast are some of the
innovative measures employed on the Magnificent Mile Courtyard
by Marriott in downtown Chicago.
The 23-story structure at Ontario and St. Clair streets, which
previously held parking, consists of a ground floor devoted
to lobby and restaurant space, eight floors of parking above
that and then the 14-story hotel tower. Kraig Ribock, project
manager for construction manager Bovis Lend Lease of Chicago,
estimated the total cost at about $40 million.
Hotel Above Parking
Lawrence Hodak, project manager with project architect Mann,
Gin, Dubin and Frazier Ltd. of Chicago, said the project entailed
putting the hotel's structural grid on top of a nine-story,
post-tensioned, double-helix parking ramp on a 100- by 300-ft.
site.
He added that the project's biggest hurdle was the structural
aspect of placing the hotel floors, with a footprint of 10,800
sq. ft., on top of the 13,000-sq.-ft. floor plate of the lower
floors.
"We had to transfer the weight of the columns from the
exterior to somewhere inside the structure, so we needed huge
transfer beams," said Phil Schwartz, superintendent with
Bovis. The beams are 6 ft. wide and 9 ft. deep.
Brian Pavlovec, senior associate with structural engineer Magnusson
Klemencic Associates in Seattle, added: "We looked at steel,
but that is really uncommon to do in hotels and residential
towers because you can often use the underside of a concrete
slab as a ceiling for the floor below.
"I think another reason these structures favor concrete
is the significant acoustic concerns in hotels and condos."
Pouring such large transfer girders in the tight confines of
the project required some careful planning.
"Originally those beams were to be poured all at once,"
Schwartz said. "We would have had to shore all the way
to the basement, which would have hurt us with all the ductwork
and electrical gear going in."
The solution was to pour the largest beam in multiple lifts,
using a higher-strength concrete than originally called for
and adding a little rebar.
"We poured 2 ft. and let it cure to the strength we needed,"
Schwartz said. "Then we poured 5 ft. and let it cure, and
then we poured the last 2 ft. along with the floor."
Timing is Everything
Bert Brandt, project manager with Bovis, said the parking
structure on the lower floors of the building opened at the
end of May, 13 months after construction began. The hotel portion
of the structure is scheduled to open in late autumn.
"The site was so small that we had to place a tower crane
in the middle of the building," Brandt added. Holes were
left in the deck slabs as the building went up to create room
for the crane, which remained inside the building for eight
months. It worked from three different levels within the structure,
reset twice as the building went up.
Brandt said the building had to be topped out and the tower
crane removed in time for crews to close up the deck slabs and
complete the finishes so that that the garage could open on
schedule. A 500-ton ground crane was used to remove the cab
and then pull out the remainder of the crane piece by piece.
A new Chicago regulation enacted for public safety after a crane
accident a couple of years ago added urgency to the crane removal,
Brandt said.
"The city requires that there cannot be a tower crane above
an occupied building," he added.
The city's crane requirement meant that all lifts for the construction
of the hotel floors had to be done before the structure's lower
garage floors could be occupied.
"We had to get the roof on and get all the systems in place
and elevators working and make sure the garage ownership was
able to move in and operate and manage this property while the
rest of construction continued," said Schwartz.
Logistics also dictated use of an exterior monorail system to
hang the precast concrete on the exterior of the structure's
lower 10 floors.
"The system was nothing more than a couple of beams that
cantilever out from the building," Schwartz added. He said
the beams carried a pulley system that lifted precast panels
from the ground and up to the point of installation. The pulleys
operated two floors above the point of installation.
"We could have used a ground crane, but we would have had
to close down the street," he said. Closing the street
would have been extremely costly.
Schwartz added that this type of precast installation has only
been used on a few - and smaller - Chicago projects.
Presenting a Unified Front
Hodak said the building is not a true Art Deco building, but
rather a structure with massing and interior detailing inspired
by architecture of that period.
"The vertical lines and the vertical streamlining all recall
that era, but it's not a true deco design and it's not overdone,"
he added.
A small snag was encountered in matching the color of the poured
concrete to the precast on the building's exterior.
"We had mock-ups set up, but we didn't have them in the
right locations," Hodak said.
Differences in texture between the two surfaces created a different
color, depending on the weather conditions and the time of day.
"We finally got a color that works well," he added.
Working in Close Quarters
Keeping the surrounding streets and building foundations unscathed
by construction required a system of corrugated sheeting around
the project's tight site.
In addition, because there was no storage space, all materials
had to brought onsite for just-in-time delivery.
"I had to manage hour slots when they could and couldn't
deliver," Schwartz said. He added that just getting trucks
on and off the site was tough in the close confines.
"Nobody could park onsite," he said.
With no room for trailers onsite, the trades set up shanties
on the garage level until the structure opened for business.
Brandt added that the building's post-tensioned concrete structure
required a lot of communication with the MEP trades because
of the enormous amount of embedded plumbing, conduit and so
on for mechanical systems.
"We brought the MEP contractors onboard very early,"
and the structural engineer was heavily involved with placing
piping and conduit in the floors, he said. |
print this page
e-mail this page
