Office with Design Ellipse Adds Twist to Construction

Impurities removed, wetlands preserved on site of Northwestern Mutual's office
May 2003

by Elaine Schmidt

The $125 million Northwestern Mutual office building and parking structure under construction in the Milwaukee suburb of Franklin features a distinctive design, flexible HVAC system and an infrastructure designed to accommodate three additional construction phases over the next 20 to 25 years.

The geometry of the structure's elliptical focal point, a tight schedule and a site that required some demolition, soil removal, dewatering and careful handling of wetland areas make it an "intriguing" project, said Matt Bratzke, project manager for construction manager and general contractor Opus North Corp. of Milwaukee. Work began on the site in March 2002 and is slated for completion in March 2004.

Designing an Ellipse

The biggest construction issue has been the elliptical shape of the entry structure, which ties the two main wings of the building together, Bratzke said. Protruding from the "elbow" of the L-shaped, five-story building, the structure will house a two-story lobby, with conference spaces on the upper floors.

Its glass facade, which will be lit at night, will be the focal point of the campus.

"This is actually a quasi-ellipse," said T. J. Morely, design architect on the project for Eppstein Uhen Architects of Milwaukee and Chicago. "Everyone thinks it is an ellipse, but it is far from a true ellipse."

Morely said the drafting program his company uses makes a distinction between a true ellipse and a polyline ellipse.

"The choice was to draw a bona fide ellipse or to use the drafting program," he said. "The feeling was, let's just use the drafting tools. Little did we know that would cause a bit of confusion, especially for the trades who were in the midst of having this thing described as an ellipse and laying it out mathematically only find that it was not working."

All of the interior walls of the structure follow the quasi-elliptical shape, meaning that every trade from the glaziers to the fabricators and installers of the hand rails, window mullions and exterior stone panels needed clear, precise drawings.

"We developed about 10 drawings that documented the geometry and shared computer files with the subcontractors," Morely said.

Shane Denison, design drafter for subcontractor Concrete Technology Inc. of Springboro, Ohio, said things went smoothly. "The architect provided quite a bit of information on architectural drawings that we used as work points around the ellipse," he added. "The computer files provided a way for us to double check that our work points were overlaying correctly."

Overcoming Site Issues

Several site concerns were addressed before work could begin.

Bratzke said the site is a compilation of several parcels of land, one that previously held a 19th-Century school building and the other a drive-in theater.

The drive-in presented a few demolition issues.

"There was transite siding on the movie screens," Bratzke said. "This is an asbestos product, like a cement board, that was used in the '50s. It was durable and fire-resistant."

Although the asbestos in the transite siding is nonfriable, Bratzke said that once it has been broken, the Wisconsin Department of Natural Resources requires special handling. It was hauled to a landfill approved to accept such potentially hazardous materials.

The old school also contained some asbestos.

Cars had parked on the drive-in's gravel lot for 50 years, leaving a residue of petroleum products.
Bratzke said the lot had also been sprayed periodically with oil to keep dust to minimum.

"We spent a few hundred thousand dollars removing these types of materials," he added.

Additional site concerns arose when the DNR and the Army Corps of Engineers found several pockets of wetlands on the site.

"It took a lot of effort planning for four buildings and four parking garages in the master plan and working around these wetlands, which were not in the most convenient places," Bratzke said.

Morely called wetlands "sacrosanct" and added that they had to be preserved in the project's design and protected throughout construction.

"We put up a silt fence to protect the areas and a very visible, orange construction fence to keep contractors from taking a shortcut," he added. The worry about shortcuts stems from the fact that in winter, the wetlands do not appear to be wetlands and can easily be missed.

Morely said the wetlands are tied into the site's design via a water feature, a flowing river and waterfall, which will connect the largest of the wetlands visually but not physically.

Once construction began, high water levels became an issue.

"The water levels really impacted foundation installations," Bratzke said. Solutions included sinking a well a few feet from footings to drop the water level.

He said that initial soil testing indicated some spotty conditions, with water in some areas. What wasn't expected was a pocket of purged water trapped between layers of underground soil that crews broke into.

"We had water just spouting out of the ground," Bratzke added. "It happened right before a pour, with trucks on the way. At that point you stop everything and try to get rid of that water."

Spotty conditions included soil with a limited bearing capacity.

"In some places we had to remove soil until we got to good soil that met the bearing requirements," Bratzke said. He said that in some areas, workers had to excavate and pour a lean, 1,000-psi concrete mix to seal off the footings from water. Soil and water issues consumed several weeks.

Meeting Deadlines

The schedule provided an obstacle.

"We started this project toward the end of November or the beginning of December 2001," Morely said. "Northwestern Mutual and Opus North challenged us not only to develop a building design, but also to create a master plan for the roughly 2 million sq. ft. on the site."

He added that the schedule dictated the first bid package, for site grading and utility footings, be sent out while the entire site plan was finalized so the utilities could be put in place for all the buildings planned on the site over the next 20 to 25 years.

"We developed a series of design and production teams where master planning, programming and building design were three components that ran on parallel tracks and fed into each other," he said. Teams toured 50 to 60 different buildings around the country and constructed numerous models and computer animations.

"The challenge was that we had to make decisions and then live with them," Morely said.

Planning for the Future

To facilitate the master plan for the site's future development, a central utility plan had to be constructed with this first phase of development.

"The central plant is to the north of this building, and we have to run all the piping, which is sized for those future buildings, through this building," Bratzke said.

The huge pipes will be put in place and capped off until future construction is ready to tie into the system.

The central plant includes two generators that will prevent data loss during power-source interruptions and allows the owner to generate energy to offset peak electrical demand.

Within the structure, a 14-in. raised flooring allows HVAC systems, electrical wiring, phone, data and computer cables to be run beneath the flooring., simplifying climate control and future shifts in work-space usage.

"We are distributing air through pressurized plenums under the raised-access flooring," Bratzke said. Air will flow through more than 2,000 9-in. holes in the floor, capped by metal diffusers that can be easily opened or closed by individual occupants.

The plenums take up far less space than traditional forced-air ducts. Mini reheat boxes on the perimeter of the building will wash the windows with air, preventing cold spots along the windows.

The site is as much a part of the project as the structures. An exposed lower-level cafeteria that effectively creates a six-story facade on one wing of the structure will look out over a patio, pathway and water feature. The water feature includes a waterfall that flows over the underground tunnel that will eventually connect to future structures.

Extensive tree and prairie plantings will ensure a sustainable, green environment.