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Report: CA Tower's Sinking Did Not Crack Window

Wednesday, October 24, 2018

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A new report has dismissed the idea that the sinking of San Francisco’s Millennium Tower is what caused a window to crack on the 36th floor.

Architecture and engineering firm Allana Buick & Bers released a report last week that concluded that the crack—which appeared over Labor Day weekend—was caused by “exterior impact.”

What Happened

According to the San Francisco Chronicle, the crack was discovered around 2:30 a.m. on Sept. 1, when the unit owner awoke to a “massive” banging sound.

Hydrogen Iodide, public domain, via Wikimedia Common

A new report has dismissed the idea that the sinking of San Francisco’s Millennium Tower is what caused a window to crack on the 36th floor.

“This sound was so massive in scale, it sounded like a huge, thick vault door had just slammed shut,” the homeowner said, noting that over the next 30 minutes it sounded like the glass in the window was splintering.

The incident sparked widespread concern that the tower’s infamous settling issue was to blame for the crack, and that more damage would occur.

The tower has sunk at least 18 inches and tilted 14 inches to the west and 6 inches to the north since it opened in 2009. The 58-story tower sits on a 10-foot-thick mat foundation, held in position by 950 reinforced concrete piles that are sunk 60 to 90 feet into clay and mud but do not reach the bedrock, which is what the settling is attributed to.

To fix the leaning issue, engineers are suggesting boring 275 to 300 steel and concrete “micro piles” down to bedrock, only on one side of the building at a time, starting with the west side. Once the structure is stabilized, the east side would be allowed to sink until the building straightens itself. Then, micro piles would also be driven into that side, preventing the structure from sinking any further. Repairs are slated to take two to five years.

The Report

After Buick & Bers filed its report, the city’s Department of Building Inspection also had an independent engineer from Standford University, professor Greg Deierlein, review the report.

Deierlein concluded that there was no reason to further investigate, but did advise that the overhead scaffolding that has since been installed around the window to protect the street below remain intact until the window is replaced, which has a deadline of Nov. 18.

The building’s management has said that a new window has been ordered from Shanghai, so the replacement likely won’t take place until next month. The window, once removed, will also be inspected, and a visual inspection of all similar windows in the tower is to be completed by Dec. 21.


Tagged categories: Condominiums/High-Rise Residential; Good Technical Practice; Health and safety; North America; Safety

Comment from Andrew Piedl, (10/24/2018, 8:43 AM)


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