A luxury residential tower in San Francisco that won engineering awards when it was opened in 2009 is sinking and leaning, sparking fears among residents and claims for damages.
More than 160 owners of condominiums have appealed to tax authorities, saying the value of their $1m-plus properties have plummeted, in some cases to as little as 0$.
Some of the approximately 400 owners have begun legal action against the developer after it emerged that the 58-storey Millennium Tower, at 301 Mission Street, had sunk 16 inches and was leaning, according to reports, by as much as 7.6 inches off the vertical at the tower’s top.
Millennium Tower as seen from Fremont Street (MichaelTG/Wikimedia Commons)
Their concerns are heightened by the fact that San Francisco is prone to earthquakes.
Millennium Partners, the developer, have in turn blamed "dewatering" caused by a major excavation next door, where a $6bn rail and bus transit hub is under construction.
But the transit hub developer, a public body called the Transbay Joint Powers Authority (TJPA), denies its project is to blame and says the unusually heavy Millennium Tower has inadequate foundations that do not touch bedrock.
Millennium Partners and the mayor of San Francisco have assured residents they are safe, but cracks are reported to have appeared in the basement level and on sidewalks outside.
Questions are now being raised over how much Millennium Partners knew about the tower’s settling into the ground, which consists of clay dredged from the bay. On 20 September the City Attorney, Dennis Herrera, subpoenaed the developer to disclose what it had told condo buyers.
"I feel I was duped. I was sold a lemon," resident Paula Pretlow told NBC News. "If I had any inkling whatsoever that I was buying a building that was settling, sinking, and tilting, I never would have done it. I would not have made this investment."
Made of reinforced concrete rather than steel, the 645-foot (196.5m) tower is the heaviest building ever built in San Francisco by pounds per square foot, its engineers, DeSimone Consulting Engineers, said when the structure had been finished in 2008.
It was also the tallest residential building in the US west of Chicago, the tallest reinforced concrete structure built in a seismic zone 4 region, and the fourth tallest structure in San Francisco, DeSimone engineers wrote in a paper at the time.
Artist’s render of the rail concourse of the Transbay Transit Center under construction next to the sinking Millennium Tower (TJPA)
They said the tower is supported by a mat foundation resting on 950 piles, weighing 130 tons each, with each descending to a depth of around 80 feet.
In describing the Millennium Tower project on its website, DeSimone says that by using performance-based design as well as code-based design, it was able to "optimize the design of the perimeter frames and reduced their sizes more than what would typically be allowed by code".
The project won a number of structural engineering awards in 2008 and 2009.
Buildings do sink. Millennium Partners’ own geotechnical engineers, Treadwell & Rollo, had predicted that the tower would settle vertically a maximum of 5.5 inches over 20 years.
I feel I was duped. I was sold a lemon– Paula Pretlow, Millennium Tower resident
But the issue of its abnormal sinking, and tilting, hit headlines on 1 August this year when newspaper San Francisco Chronicle reported that condo owners were concerned, and had retained a number of engineering consultants to investigate the issue, and were evaluating their legal options.
In comments to media Millennium Partners immediately blamed groundwater pumping at next door’s TJPA’s Transit Center for causing the excessive settling, and on 4 October backed up its claim with a report it had commissioned from Sage Engineers, which said continued dewatering of the Transit Center "is likely contributing to ongoing and future settlement of the building".
On the same day, however, TJPA returned fire with a dossier which it said rubbished the developer’s claims.
TJPA said it had been warning Millennium Partners about excessive settling since 2010. Furthermore, TJPA said, it had only begun dewatering in May 2013, by which time the heavy tower had already sunk 12 inches.
The blame, insisted TJPA, rested squarely on the tower’s "deficient foundation" which it said is is not up to the task of supporting such a heavy structure.
TJPA presented data, prepared by UK consulting engineer Arup, which showed that the Millennium Tower exerts a net pressure four to five times that of the next largest building on the perimeter of the Transit Center, 555 Mission Street, and more than 50 times the net pressure of another building, 199 Fremont.
This table compares the net pressure exerted by Millennium Tower to other buildings. "Ksf" is kips per square foot, where a kip is 1,000 pounds (TJPA)
"Of course, had [Millennium Partners] supported the Tower on piles down to bedrock, the Tower would not be tilting today," it said in its dossier.
Headache for all
The issue is hugely complex and will cause grave difficulties for all involved.
"This is a unique situation. I’m not sure how [we] are going to handle it," Alistair Gibson, executive secretary of the city’s Assessment Appeals Board, told the San Francisco Examiner. "We don’t know what’s going to happen with that building. There are going to be other issues involved."
The residents and the developer face potential losses on their investments, and the TJPA’s Transit Centre may also be at risk. Last month the San Francisco County Transportation Authority Commission voted to withhold a tranche of funding worth nearly $6.8m for the project, citing concerns about the sinking tower and cost overruns.
The TJPA itself has received claims for damages.
Meanwhile, San Francisco’s mayor Edwin M. Lee has instructed city officials to amend the city’s earthquake safety plan to require a review of soil conditions and mandatory earthquake evaluations during property sales, reports the New York Times.
A second public hearing on the tower’s safety is due to be held next week, NBC News reported.
Top image: The Millennium Tower in San Francisco, photographed August 2016 (Frank Schulenburg/Wikimedia Commons)