60-Story Structure

300 N. LaSalle Office Embraces Chicago River

by Elaine Schmidt

Although the skyward reach of the 60-story 300 N. LaSalle St. office under way in Chicago draws attention upward, some of the most interesting features actually require a downward glance.

An environmentally friendly cooling system that draws water from the Chicago River as well as a public, terraced plaza on the river make the $230 million, 1.3-million-sq-ft project as interesting at and below grade as above.

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“We’re bringing the river into the building through a series of grates and pipes to a river water vault,” says Doug Alvine, president of Omaha, Neb.-based Alvine Engineering, the MEP engineer. From there the water is pumped through the chillers that are designed with marine boxes that allow the water to function as a heat exchanger medium.

The cooling system will function year-round, offsetting the heat generated by the thousands of people and computers that will occupy the building.

Scott Timcoe, vice president of Houston-based Hines, the developer, says there is a small net savings on the initial cost of the system over the cost of a traditional chiller system.

“There is another savings, a big savings, in future utilities costs,” he adds. The building will avoid using more than 5 million gal of potable city water each year thanks to the river water.

Drawing from the River

Many Chicago buildings draw river water for various uses, but buildings going up on a site that has never drawn from the river before have to meet rigorous standards to get permits.

The two biggest permitting issues for this project were draw velocity and temperature.

“You have to limit the velocity of the water at the intake to guard against fish impingement so that you’re not pumping so fast that fish will get swallowed up by it,” Timcoe says. In addition, the water that the building returns to the river cannot be more than 5 degrees warmer or cooler than the water that was removed, to avoid impacting the environment.

The water will pass through filter screens to protect the cooling system from whatever matter might be in the water, Alvine says. The water will be cleaner when it’s returned to the river than when it was drawn in, he says.

One river element, a pollutant of sorts that has entered the Great Lakes system through the St. Lawrence Seaway, cannot be filtered out.

“Immature zebra mussels are going to get through,” Alvine says. “You can’t do a level of filtration to prevent it, so you just have to plan on it as part of your routine maintenance.” The mussels are difficult to filter because they are minuscule in their immature state, multiply quickly and adhere to anything.

The building will include three levels of below-grade parking, retail and restaurants.

Steel with concrete core will support the structure. Unitized aluminum curtain-wall cladding with stainless steel accents will dress the structure.

Construction activity started in June 2006, and the project is expected to be complete in July 2009.

Water, Water Everywhere

Building on a tightly constricted river site that had a long history of use presented several issues in the building’s design and construction, says Ron Klemencic, principal of Seattle-based Magnusson Klemencic Associates, the structural engineer.

“Because the site is right on the river, there is a river wall or bulkhead,” he adds. “Behind that river wall we are building not only the tanks and intake structure for the cooling system [all of which will be covered by the terraced plaza] but also digging a hole below grade for three stories of parking—and not letting it flood.”

The river wall was in reasonably good shape and did not need replacing but did need strengthening. That combined with a pile-supported foundation for the parking garage and plaza did the trick.

The site’s history presented some physical obstacles as well.

“There aren’t detailed drawings on a lot of the stuff that’s down there,” Klemencic says.

He says a warehouse was built on the site in the 1800s. It was torn down in the 1950s and replaced by a parking garage. Both the timber pilings from the warehouse and the concrete caissons from the garage are still underground on the site.

“None of the columns for the new buildings aligned with those caissons so we had to design around them,” he says.

Yet more history was found in an abandoned, underground freight tunnel that cuts across the site. The tunnel was used during the 1800s and early 1900s to move coal around the city.

Stephanie Calhoun, project manager for the Maryland-based general contractor Clark Construction, says the tunnel runs under the site in a U shape. To keep the tunnel from collapsing under the weight of the completed building, reinforced bulkheads were constructed.

A total of 34 bell caissons have been installed to support the building, 10 of which measure 26 ft wide, Calhoun says.

Soldier piles and internally braced lagging were used in the construction of the building’s concrete core. The core had to be brought up to grade before digging could begin for the perimeter of the structure.

“For the perimeter we removed the top layer of dirt and installed the first layer of whalers and bracing back to the core,” Calhoun says. “Then we would dig down and brace again, working in a corkscrew pattern around the core.”

Look Up

The building’s designers have been acutely aware of making a positive impact on the city’s skyline.

“The desire was to create an iconic building,” says Tony Marchese of New Haven, Conn.-based design firm Pickard Chilton.

Acknowledging some of the great architects of Chicago’s past, such as Louis Sullivan and Frank Lloyd Wright, whose work stands in the city today, Marchese says the building’s stepped silhouette and the architectural details in its uppermost stories will make it “look and feel like a Chicago building and acknowledge those traditions. It will be classic and modern.”

The classic style will be reflected in the subtle setback and nod to Gothic detail with the lines at the top, and the modern style is shown in the gleaming, sleek exterior.

To take advantage of the great potential the 200-by-220-ft site offered, the designers “slid the tower” to the northern edge of the site, leaving an open area on the river. A public plaza, overlooked by the building’s three-story lobby, was created on terraces that descend to the river.

The structure received a LEED gold precertification. The building’s river-water cooling system plays into that certification, as do elements like floor-to-ceiling low-emissivity glass and the H-shaped floor plans that draw natural light deep into each floor.

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