Vertical Extension

33-Story Blue Cross Tower Sprouting 24 More Floors

by Craig Barner

Like preteens everywhere, the 11-year-old Blue Cross-Blue Shield Tower in Chicago is experiencing growing pains.

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The metaphor is somewhat literal in the case of the East Randolph Street office building. The 33-story structure in the Loop is getting an additional 24 floors as part of a $270 million vertical extension.

Vertical extensions are “quite rare,” says David Scott, chairman of the Council on Tall Buildings and Urban Habitat in Chicago, an international organization of engineers and architects, and principal in New York of London-based Arup, an engineering, design and planning firm.

When they occur, they are usually done because of rezoning that allows for taller buildings or development in exceedingly building-dense areas that can grow only by going up, such as in Hong Kong. There, Arup recently oversaw a 30-story vertical extension of a 15-level building.

Back in Chicago the original architect of the Blue Cross-Blue Shield, Lohan Associates Inc.—now Goettsch Partners—designed the tower so that its owner, Health Care Service Corp., could expand the building if needed.

That time is now.

“We’ve outgrown the facility,” says Andy Pini, vice president of corporate real estate and development for HCSC, the operator of the Blue Cross insurance plans in Illinois and three other states. About 4,200 people work in the existing 1.4 million-sq-ft building. When the extension is done in November 2009, Pini says the lengthened, 2.3-million-sq-ft tower will hold about 8,000 people. Goettsch is serving as the architect on the extension project as well.

Pain of Logistics

Lou Rossetti has likely experienced the most pain of anyone associated with the Blue Cross project. As senior project manager for Chicago-based Walsh Construction Co., the contractor, he has overseen the project’s intricate logistics.

Excluding early project elements, five months were needed to carry the logistics of the extension. Planning involved the creation of a three-dimensional, color-coded model in scale to visualize the placement of 230 tons of steel, both temporary and permanent, to form a grillage system with platforms. The grillage is being used to support four different lifting systems: a 17-ton derrick, 35-ton derrick and two Potain 605 tower cranes.

“So 230 tons of steel was erected and [some of it] taken out and scrapped just to get the tower cranes in place,” adds Jim D’Amico, vice president of Chicago-based The John Buck Co., the project’s development manager.

In October the individual sections of the 17-ton derrick manufactured by Woodstock, Ontario, Canada-based Timberland Equipment Ltd. and some initial grillage were lugged 500 ft to the northwest corner of the roof via a service elevator with 6,000-lb lifting capacity, Rossetti says. About 30 to 40 loads were needed.

The derrick was constructed on the roof’s northwest corner so that building materials could be lifted from two ground-level staging areas: a plaza north of the building and a lane of Columbus Drive to the west.

Ensuing work gradually progressed east across the north half of the roof.

Once the derrick was in place, the grillage was extended, including a platform to hold the 35-ton derrick, Rossetti says. The platform, made up of temporary and permanent steel, was planted in the existing building columns that had previously been stubbed up.

“Once the grillage was in place, we erected the 35-ton derrick,” Rossetti adds.

The succession of derricks was necessary. Although the 17-ton derrick was the largest capable of being transported to the roof via the service elevator, it could not erect a tower crane.

After the 35-ton derrick was erected, it was used to disassemble the 17-ton derrick, whose pieces were returned to the ground. Then, more grillage was assembled to hold the first tower crane.

First Crane Erected

Once the grillage had been extended, the first tower crane was erected. A key issue was making sure the boom of the derrick could reach high enough to place the 160-ft-long boom of the tower crane.

The base of the derrick had been elevated an additional 3 to 4 ft via the platform to ensure the derrick could reach the connecting point on the crane for the boom. “It was close” but successful, Rossetti says.

But the mass and positioning of the steel members of the grillage required to support the east tower crane could not be set by the west tower crane or the remaining derrick as it was positioned. As a result, the west tower crane was used to build a second platform made of temporary and permanent steel as part of the grillage system and to reposition the derrick to the east side of the roof.

From the new position, the derrick was used to place more grillage to support the second tower crane.

Grillage Design

Seen from the sky, the grillage with platforms was rectangular and was seemingly continuous.

Accommodating the tight site on the roof and ensuring the lateral stability of the cranes against Lake Michigan’s brutal winds were major issues in the grillage design, says John Matuska, senior project manager of Farmington Hills, Mich.-based Ruby + Associates, the grillage structural engineer. As a result, the system featured heavy members, multiple splices due to the space constraints and 3-ft.-deep plate girders as connections between steel members.

“I would call those elements significant, both the frame work and the connections,” adds Charlie Carter, chief structural engineer with the Chicago-based American Institute of Steel Construction Inc., a national organization.

Another issue was working at an elevation of 500 ft adjacent to the lake shore with its fierce winds. Crews erecting the tower crane shut down for slightly more than 30 days.

“When erecting a crane, city of Chicago rules say you cannot continue when wind is in excess of 30 mph,” Rossetti adds.

When both tower cranes were assembled, the work to build the 24 floors could commence. In mid-March both cranes were functioning, the first new floors were being added to the tower and the Blue Cross-Blue Shield Tower was growing.

Building’s ‘Tu-Tu’

Prior to the start of work, crew members seeking tips had toured the Bentall Five tower, a 21-story building in Vancouver, British Columbia, Canada, that had received a 13-story addition. The Canadian team emphasized safety.

With this in mind, several unusual measures were incorporated in the Blue Cross project to minimize danger.

Below, a canopy on the sidewalk surrounding the building to protect pedestrians is so substantial that it cost more than $1 million. The canopy was clad in finished plywood to make it less unsightly to the building occupants. Above, a 10-ft-long safety platform—sometimes referred to as the “tu-tu”—will extend horizontally from the extension.

“We have several different levels of defense to make sure a bolt, wrench or something doesn’t come from the building onto the sidewalk,” Rossetti says.

Orange netting installed for safety reaches the length of two 30-floor atria being converted to elevator shafts to hold 16 new elevators.

SIDEBAR

Avoid Blues about Building Color

Color not only plays a prominent part in the name of the Blue Cross-Blue Shield Tower—it was foremost in the minds of the architects involved in the $270 million vertical extension of the building.

Designers were challenged to match precisely the curtain wall of the existing 33-story tower with that of the 24 levels to come. The existing blue-and-gray curtain wall was made up of an aluminum frame, low-emissivity glazing, vertical granite accents and horizontal stainless-steel accents.

“Consistency of exterior materials was essential,” says Andy Pini, vice president of corporate real estate and development of Chicago-based building owner Health Care Service Corp. Otherwise, a lack of precise match would be embarrassing, Pini adds.

A switch in curtain-wall suppliers compounded the challenge. The original supplier was Toronto-based Antemex International, but the supplier for the extension is Italy’s Permasteelisa Group SPA.

“Both were asked to submit proposals,” says Joseph Dolinar, partner with Chicago-based Goettsch Partners, the project architect. “It (the selection) had to do with Permasteelisa’s ability to support the building schedule.”

Complicating the issue further, the supplier of the original stainless-steel pattern is no longer in business. Samples from the new supplier were acquired for comparison.

“We put the samples next to the building, and they matched up well,” Dolinar says.

Taking the issue a step further, selected areas of the exterior were cleaned and compared with the samples. Dirt had built on sections of the building over the years.

“We could not tell any difference between the old and new,” Dolinar says.

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