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$100M CA Millennium Tower Fix Approved

Wednesday, July 29, 2020

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The permitting process is reportedly now complete for the fixes needed for San Francisco’s Millennium Tower. The $100 million shoring project is now estimated to begin in November.

Since its opening, the building has reportedly settled more than 17 inches to the northwest.

Tower Saga

Opened in 2008 at the cost of $350 million, the Millennium Tower was designed by Handel Architects, with structural engineering by DeSimone Consulting Engineers. Webcor Builders was the general contractor on the job, according to the Concrete Reinforcing Steel Institute.

Almost a decade after completion, in August 2016, the San Francisco Chronicle reported that Millennium condo owner John Eng had filed a lawsuit against both the building’s owners, Millennium Partners, and the Transbay Joint Powers Authority, whose nearby construction may have caused the tower to begin sinking and tilting.

In the complaint, the plaintiff calls the building “defective,” and claims Millennium Partners “knew that the Millennium and Subject Homes were not of marketable or habitable quality." The suit notes that the building sits on a manmade “mud fill” in an area that was once underwater, and asserts that the decision to build on a concrete slab and 80-foot piles instead of piles anchored into the 200-foot-deep bedrock was made “to cut costs.”

Hydrogen Iodide, public domain, via Wikimedia Commons

The permitting process is reportedly now complete for the fixes needed for San Francisco’s Millennium Tower. The $100 million shoring project is now estimated to begin in November.

The suit also stated that, “over time the building most likely will sink an additional 8 to 15 inches into the landfill” over which it is built, and the tilt, currently measured at about 2 inches toward the northwest, could also get worse. According to the suit, cracking and buckling were also visible in individual units and in the building’s commons area.

By February 2017, a government oversight committee began conducting hearings in an effort to determine what went wrong to cause the building to sink 16 inches and tilt 2 inches. According to reports during this time, Millennium Partners also hired Sage Engineers to investigate the foundation issues and potential solutions.

That spring, the tower saga grew as the building’s homeowner’s association sued the developer and others for more than $200 million in damages to the residential structure. At the time, the lawsuit was the only one in the litany of litigation that sought a permanent fix.

Continuing into the summer, by mid-July, the NBC Bay Area Investigative Unit reported another issue with the Millennium Tower—gaps in the curtain walls of at least one unit, ultimately posing a fire hazard. Should a fire start in the unit below, it was predicted that it would easily spread upward, with high chances of causing various smoke damage.

Within the same month, the tower reportedly sunk another inch, but officials had finally reached a possible fix, should an agreement be reached. According to the LERA firm and DeSimone Consulting Engineers, the problem could be both stabilized and somewhat reversed by adding 50 to 100 new piles down to the bedrock, beginning from the building’s basement. Each individual pile would be 10 to 12 inches in diameter, noted the Chronicle. The estimated price tag for the repair was reported to be between $100 million and $150 million range, although some experts feared it would exceed $1 billion.

However, by April 2018, another proposal fix was introduced: drilling holes down to bedrock in order to stabilize one side of the tower while letting the other side sink down, allowing the building to level itself out. By this time, the tower had sunk a total of 17 inches, and tilted 14 inches to the west and 6 inches to the north. Estimations for this solution ranged between $200-500 million.

In September, several months after a retrofit repair for the Millennium Tower was proposed, another issue came to light: Cracks had appeared in a 36th-floor window, sparking concerns over whether the damage was local or symptomatic of a more widespread issue.

According to reports, the issue could have stemmed from structural issues, a material defect or be a one-off event. Architecture and engineering firm Allana Buick & Bers was hired by skyscraper residents to help determine what caused the damage.

Over time the tower’s saga has seen roughly 146 lawyers involved in nine different lawsuits filed regarding the structure’s various issues.

In September, an independent four-person panel—hired by the city and headed up by Stanford engineering professor Gregory Deierlein—after meeting 11 times with design teams from engineering firm Simpson Gumpertz & Heger for the proposed changes, approved the shoring fix.

In a letter addressed to the City and County of San Francisco Department of Building Inspections at the time, the panel—made up of Gregory G. Deierlein, Shahriar Vahdani, Marko Schotanus and Craig Shield—announced that by adding new piles to the structure, chances of future sinking should be reduced, in addition to improved seismic performance.

Since then, the plan has gone through a rigorous approval process.

What Now

“They city and state had a plethora of permit requirements for us," said Ronald O. Hamburger, a Senior Principal with Simpson.

The plan how now been approved by the San Francisco Board of Supervisors, the Port of San Francisco and the State Lands Commissions, as well as passed an environmental review under the California Environmental Quality Act. Three Department of Building Inspection permits are also secured.

Currently, the tower sits on 950 reinforced concrete piles that have been driven up to 90 feet deep into bay mud.

The process will involve drilling and jacking 52 concrete piles socketed more than 30 feet into bedrock under the north and west sidewalks. These piles would support a new mat section, or collar, tied into the existing mat.

The piles are reported to be 2 feet in diameter and weigh 140,000 pounds. The process will also relieve stress on the compressed soil located underneath the north and west sides of the building.

   

Tagged categories: Condominiums/High-Rise Residential; Engineers; Health & Safety; Health and safety; NA; North America; Safety

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