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City Slicker

Chicago's latest Class A spec office tower is winning big in a tough market, thanks to the well-executed efforts of its Building Team.

May 01, 2006 |

At a time when many developers are fleeing the stagnant office market for more profitable sectors like multifamily residential and retail, Chicago developer John Buck continues to churn out winning speculative office buildings.

Buck's latest success story, the 1.46 million-sf, 53-story 111 S. Wacker Dr. tower in Chicago's West Loop, which opened last May, is more than 90% occupied and is commanding premium lease rates in a local office market that's overripe at best. It's practically déjà vu for the developer, who overcame similar odds in 2001 in selling out his last major project: the 50-story UBS Tower at One N. Wacker Dr.

"Everything John Buck touches seems to turn into gold," said Building Team Awards judge Daniel Murphy, PE, LEED, with Environmental Systems Design, Chicago, referring to the success of 111 S. Wacker Dr. and UBS Tower.

Murphy and the other members of Building Design & Construction's 2006 Building Team Awards judging panel praised the Building Team for 111 S. Wacker for finding a way to win in Chicago's tough spec office market, while creating a bold modern structure that more than holds its own architecturally among the giants, notably Sears Tower and UBS Tower, along Wacker Drive.

The judges also commended the Building Team's efforts in achieving a Gold rating in the U.S. Green Building Council's LEED Core and Shell program—the first building to earn such an honor.

For that, the project earned a Silver Award in BD&C's 2006 Building Team Awards.

Like many great office buildings, 111 S. Wacker features a showpiece lobby finished with high-end materials and lively design elements.

The concrete core is clad with a textured, white Carrara marble that contrasts with a solid wall of red Rossa Verona enclosing the lobby on two sides. The spiraling form of the parking ramp directly above the lobby is expressed in the ceiling, which spirals and steps in 10-foot increments, eventually reaching its full, two-story height on the north-facing side of the building.

The site measures just one-fourth of a block and abuts a 14-story building on the east side. To compensate for the extremely tight site, the Building Team had to go through great pains to keep the building open and spacious at the lobby level. "We wanted to make sure that when you're in the lobby, it didn't feel like you're in a quarter-block building," says Steve Nilles, AIA, LEED AP, partner-in-charge for the project with Goettsch Partners.

To minimize columns at ground level, Seattle-based structural engineer Magnusson Klemencic Associates designed six massive V-shaped column transfers at the 10th level that diagonally transfer loads from the building's typical perimeter columns, spaced 40 feet apart, to six mega-columns spaced 80 feet apart. The transfers are expressed in the building's façade as a design element.

Execution involved temporarily shoring the building until construction reached the 10th floor, "when we could gather all that load and get it into the mega-columns," says Kraig Riebock, senior project manager and VP with construction manager Bovis Lend Lease. "All the temporary structural steel shoring had to be carefully incorporated into the design."

Construction of the lobby's glass cable wall system was even more complicated, according to Riebock. The wall is composed of 68 1¼-inch-diameter stainless steel cables that extend from the plaza level to the underside of the third floor. Each cable had to be carefully tensioned during the various sequences of construction based on the amount of building load at any given time.

Because not all permanent dead loads were in place at the time of installation, the construction team had to coordinate with subcontractor Mero Structures and Magnusson Klemencic to make sure the tension on the cables was the right amount at the end of the day, says Riebock. This tedious process involved tensioning and then re-tensioning each cable numerous times during a five-month span.

"For instance, when the stone paving at the plaza level was installed we had to adjust each cable to accommodate the added load from the weight of the stone," says Riebock. "Timing, sequencing, and having the correct load information were key to the success of this project."

Once the cables were installed, five-foot-square glass panes had to be attached to the tensioned strands with stainless-steel patch fittings. The entire system deflects nearly seven inches and is rated for winds loads of up to 25 psf. The low-iron panes are covered with anti-reflective coating to maximize transparency. "It's totally transparent during the day and at night," says Nilles.

The Building Team worked closely with anchor tenant Deloitte & Touche (floors 12–28 and 31) to ensure the office space would suit the tenant's needs.

Deloitte wanted a flexible, open-floor plan that would allow the firm to maximize the space and support office "hoteling," whereby employees who travel frequently share workstations with other staff members. Private executive offices would be positioned around the core of the building, with the remainder of the floor space left open for workstations and small meeting areas.

The team responded with 27,500-sf, column-free floor plates wrapped in floor-to-ceiling low-e glass to maximize daylight in the space. Perimeter columns are spaced 40 feet apart to accommodate four standard-size workstations between each column along the glass.

Designed on a five-foot module, the floor plate is also ideal for perimeter office users, says Nilles. This was key to attracting law firms like Lord, Bissell & Brook (floors 41–46). The floor plates can accommodate any combination of 10, 15-, and 20-foot offices with minimal column interference at the perimeter.

To achieve column-free spans of 50 feet in the east-west direction and 61 feet in the north-south direction, Magnusson Klemencic designed massive steel girders that extend from the building's core to the corners; these girders collect all intermediate steel members.

This approach made the coordination of construction efforts even more complicated, says Riebock. "They're deep members, and they required a lot of mechanical/electrical coordination to install the building systems in that steel framing without interfering with the tenant ceiling heights," he says.

Deloitte & Touche mandated features such as a 10,000-sf fitness center (located on the 10th floor) and a 250-seat auditorium in the conference center. The accounting firm also received goodies like a direct network connection in the conference center and additional closed-circuit TVs and entry control points throughout the building.

"We gave Deloitte & Touche the ability to in-corporate into the base building any of their tenant improvement work that we could do less expensively," says Daniel B. Jenkins, principal with John Buck who managed the design and construction of 111 S. Wacker. "That's one of the advantages to being an anchor tenant."

The team shaved at least a month off the construction schedule by reusing existing caissons from a 20-story 1960s office tower that previously occupied the site.

"It was during the latter stages of design that we realized that we were able to reuse the caissons and the majority of the existing foundation walls," says Riebock. "We were able to save on grout retention systems, and we reduced construction time by not having to form and pour new foundation walls and set as many new caissons before we could erect steel."

Of the 84 existing caissons, 81 were found to be salvageable following extensive testing of the strength and bearing capacity of the foundation elements. Testing also showed that more than 125,000 cubic feet of concrete foundation walls could be re-used.

The existing foundation system had to be beefed up, as it was originally designed to support a 20-story structure, not a 53-story skyscraper. This involved installing 24 new caissons and 28 micro-piles and pouring a 10-foot-thick concrete mat to integrate the old and new foundation elements. Over an 11-hour span, 3,600 cubic yards of concrete were poured using three concrete pumps. Each pump emptied two trucks every five minutes. Trucks were staged a block away, and drivers were notified via radio of which pump to drive to.

"At the time, it was one of the largest continuous concrete pours in Chicago history," says Reibock.

For more on 111 S. Wacker, visit: www.bdcnetwork.com/article/CA6316268.html.

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