San Francisco Millennium Tower Building, Sinking Skyscraper, Architect, Tallest SF Condo
Millennium Tower San Francisco
Tall Reinforced Concrete Structure in USA design by Handel Architects
Aug 11, 2016
Millennium Tower Building in San Francisco
Design: Handel Architects
Sinking San Francisco Millennium Tower
This high-rise building is the tallest reinforced concrete structure in the Western U.S.
The 645-foot high Millennium Tower—the tallest reinforced concrete structure in the Western United States—is sinking and tilting. The building owner is blaming the adjacent Transbay Transit Center project, reports the Architectural Record.
The 60-story residential building in San Francisco’s fast-developing South of Market area has settled 16 inches and tilted 2 inches to the northwest since its completion in 2009.
Handel Architects, with structural engineer DeSimone & Partners, designed the $350-million building. Webcor Builders constructed it using a braced soil-cement slurry wall system with 80-ft-deep soldier piles located 5 ft on center, supporting a reinforced concrete slab. A 24-in.-thick reinforced concrete shear-wall core and a partial perimeter moment frame resist lateral loads.
Developer Millennium Partners, said that though “all buildings settle over time,” the tower “settled more than originally anticipated because it was affected by subsequent construction by others.” He added that the neighboring project was “obligated to monitor and protect existing structures, and to mitigate any impacts of their work.”
Transbay Joint Powers Authority (TJPA), owner of the Transbay project, countered that Millennium Tower’s design was to blame and that the excessive settling started prior to construction.
TJPA say the design was paired with a concrete slab foundation that doesn’t reach bedrock 200 ft deep and that the Millennium Tower “is made of concrete rather than steel, resulting in a very heavy building. This heavy structure rests on layers of soft, compressible soil. That foundation is inadequate to prevent settlement of a building with the weight of the tower.”
The Salesforce and 181 Fremont towers—also adjacent to the Transit Center—are supported on piles drilled to bedrock.
Seven years of data collected by TJPA’s engineering consultants Arup before excavation began on the Transit Center showed that instead of the maximum 6 inches of vertical settlement predicted by the designer over the lifetime of the project, by the time the TJPA started work in 2010, the Millennium Tower had already settled 10 inches.
The building has continued to settle vertically to its current 16 inches. According to data collected by Arup, the tower straightened slightly during the TJPA’s excavation for the underground levels of the Transit Center, but it never tilted past vertical toward the Transit Center and is currently tilting toward the west and northwest, away from the Transit Center.
TJPA spent $58 million to install 181 overlapping, 7-ft-dia reinforced concrete piles drilled to bedrock to act as an underground buttress between neighboring buildings (including the Millennium Tower) and the Transit Center. They claim geotechnical monitoring data shows that the buttress was entirely effective in preventing excessive movement of the tower due to the excavation for the Transit Center.
While the matter is likely to result in litigation, a safety study performed by Simpson Gumpertz & Heger showed that the building is not in danger.
This story originally ran in Engineering News-Record on August 10, 2016.
Sinking San Francisco Millennium Tower Building
Millennium Tower San Francisco – Building Information
Architect: Handel Architects
Developer: Millennium Partners
Structural Engineer: DeSimone Consulting Engineers
Main Contractor: Webcor Builders
Geotechnical Engineer: Langan Treadwell Rollo
Millennium Tower San Francisco Building – Background
Millennium Tower is a 58-story, 196.6 m (645 ft) condominium skyscraper completed in 2009 in the South of Market district in downtown San Francisco. A mixed-use, primarily residential structure, it is the tallest building in San Francisco to include residences.
The blue-gray glass, late-modernist tower is bounded by Mission, Fremont, and Beale Streets, and the north end of the Transbay Transit Center site. The building was opened to residents on April 23, 2009. Its highest level, 58 floors above the ground, is listed as the 60th, because floors 13 and 44 are missing for superstitious reasons.
The US$350 million project was developed by Millennium Partners of New York City, designed by Handel Architects, engineered by DeSimone Consulting Engineers and constructed by Webcor Builders. At 645 ft (197 m), it is the tallest concrete structure in San Francisco, the fourth tallest building in San Francisco overall, and the tallest since 345 California Street in 1986. It was also the tallest residential building west of the Mississippi River when finished (later surpassed by The Austonian in Texas). The tower is slender, with each floor containing 14,000 sq ft (1,300 m2) of floor space. In addition to the 58-story tower, there is an 125 ft (38 m), 11-story tower on the northeast end of the complex. Between the two towers is a 43 ft (13 m), two-story glass atrium. In total, the project has 419 units.
The residences are said to be the priciest on the West Coast, with penthouse units on the top two floors selling for around US$12 million. The bottom 25 floors of the main tower are called Residences while the floors from 26 to the top have the name Grand Residences. The 53 units in the 12-story tower are called the City Residences. Below street level, there are 434 parking spaces in a five-level subterranean garage located under the 11-story tower. The building is located next to the site of the future Transbay Transit Center. Overall, the tower’s design is intended to resemble a translucent crystal, and is a landmark for the Transbay Redevelopment and the southern skyline of San Francisco.
Millennium Tower is also home to RN74, a restaurant and wine bar under the direction of Chef Michael Mina, located on the ground floor. Resident services include a private concierge and exclusive access to the 20,000-square-foot (1,900 m2) Club Level, featuring an owners’ lounge, tasting room and cellar, private dining room (serviced by Chef Michael Mina’s RN74), screening room, children’s playroom, outdoor terrace, and a 5,500-square-foot (510 m2) fitness center, complete with Pilates and yoga studios, massage therapy, locker rooms, Jacuzzi and steam rooms as well as a 75-foot (23 m), indoor, competition-length lap pool. A monthly events program called La Vie was launched in 2010. La Vie provides residents with monthly offerings, from film screenings in the Club Level’s screening room to celebrity fireside chats, on- and off-site winemaker events, musical performances, and more.
Address: 301 Mission St, San Francisco, CA 94105, United States
Phone: +1 415-874-4700
Location: 301 Mission Street, San Francisco, North California, USA
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