Liquid Assets: Roof-Mounted Damper Stifles Sway
in the Windy City.

Water-filled concrete tanks with internal baffles will provide counter-motion to dampen building sway to make occupants more comfortable. One expert estimates that only about 10 tuned liquid dampers are in use throughout all of North America.

By Paula Widholm

Chicago’s newest hotel/condo tower houses one of the nation’s first tuned liquid dampers, a system to ensure stillness inside when gale winds whip around outside.

The $280-million development, which encompasses 638,000 sq ft and features 188 hotel suites and 53 condominiums, opened in mid-July in Chicago’s Gold Coast.

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Major players behind development of The Elysian Hotel and Private Residences are all based in Chicago: Lucien Lagrange Architects, McHugh Construction Co., general contractor, Halvorson and Partners, structural engineer, and Simeone Deary, interior designer.

The TLD The tuned liquid damper is the latest approach to controlling motion in a tall, slender building. It offers low cost, low maintenance and high performance over a broad range of wind conditions, according to Tim Laken, senior project engineer with Halvorson and Partners.

Four enclosed concrete tanks, each 21 ft long, 18 ft wide, and six ft deep, fit within the central core wall footprint at the top of the 61-story reinforced-concrete building. Movement of water in the tanks will be controlled with internal steel baffles.

“It’s like a tub of water, and the water works against the movement of the building,” Laken says. “If there are high winds outside, we want to minimize the perceptibility of building motion for the unit owner.”

For the next several months, engineers are monitoring building acceleration and analyzing the data with computer modeling to help tune the damper system so it can be commissioned in early 2010.

Mounted on the building roof, the liquid tuned damper system consists of four concrete tanks that have internal baffles and will hold a total of about 30,000 gallons of water.

The TLD was “the most cost-effective without impeding in the architectural layout by having to increase framing member sizes,” Laken says.

The Elysian Structure The property includes two four-story steel structures for retail stores, office space, and amenities like a fitness room and pool, and four levels of below-grade parking under a richly detailed, French-inspired motor court. The first five levels of the tower house a lobby, spa, restaurant, meeting rooms and ballrooms. The next 19 stories contain two-room hotel suites with balconies.

Interior finishes include massive amounts of granite, huge water features at the entrance, elaborate mosaic tile work, and Thassos marble imported from Greece.

The tall and slender Elysian rises gracefully above the surrounding architecture. The building’s tuned liquid dampers are designed to fit unobtrusively within the building’s outline.

Mechanical floors are at levels 27 and 28 and above the penthouse. The tower columns are transferred at level 28 with a 6-ft-thick slab to accommodate the building set back at the east and west sides of level 29. Residents occupy levels 29 through 59, which have only two condominiums per floor. Column transfers at level 51, 52, 57, and 59 are supported by post-tensioned concrete beams or thickened slabs.

The Challenges Most towers this size sit atop caissons that reach down to bedrock. The Elysian, however, is supported by about 86 hardpan caissons that measure 4 ft to 15 ft in diameter and have belled bottoms. “McHugh determined we could save money by using hardpan caissons that went 85 to 90 ft below grade, as determined by the geotechnical engineer,” Laken says. “To get to rock, you’ve got to go down 130 to 140 ft, which is an expensive process.”

However, using hardpan caissons would result in a total settlement of 2 in. for the tower, roughly twice what was desired. That raised concerns about differential settlement at the interface of the 61-story tower and the four-story steel buildings located at the east and west sides.

Constructing the four-story underground parking ramp required the use of slurry walls and heavy temporary bracing.

To accommodate the condition, pour strips isolated the tower from the adjacent steel structures during construction. The pour strips were left open and the settlement was monitored during construction. Laken says, “Once the tower settled to within acceptable limits, the low-rise buildings were connected to the tower.”

Conceptual design for the traditional design-bid-build project began in 2003. Bid drawings were ready in 2006, and construction began in September 2006.

“One of the architect’s goals was to have as much open space as possible, so there’s a central core and columns around the perimeter,” Laken says. “With no interior columns, it gives flexibility to the owners for space layouts.”

This computer-generated drawing shows the Elysian Hotel’s structural members. The tuned liquid dampers are visible in gold at the top of the building.

The extremely small site, which sits about seven feet from a subway at the southwest corner of Walton and Rush streets, presented a huge logistics challenge in orchestrating the typical daily delivery of about 20 trucks of concrete, a truck of steel reinforcing bars, two trucks of precast panels, and two semis’ worth of finished goods, as well as about five delivery trucks, notes Joel Kuna, senior project manager, McHugh Construction Co.

Two towercranes were erected on site. To accommodate the activity, a parking lane on Rush Street was taken out, as well as a parking lane and a traffic lane on Walton.

The depth of the excavation for the below-grade parking dictated the use of slurry wall construction. “We had to excavate down, pour the slurry wall panels and be careful to put bracing in for the walls,” Kuna says.

The exterior is clad in 2,260 precast concrete panels manufactured by PCS in Omro, Wis. Some pieces, such as the corner cornices, weighed up to 22,000 lbs and were 24 ft long. French-inspired decorative finishes include wrought iron on windows and setbacks, and a mansard roof.

Poor weather, particularly high winds, led to the loss of 61 workdays. The city of Chicago doesn’t allow a tower crane to operate above 500 ft when winds are greater than 35 miles per hour. To keep the project moving forward during the winter, the team installed a temporary boiler on the 26th floor to heat the building, Kuna says.