SF Millennium Tower's famous lean has improved with $100M repair
All 18 of the concrete piles meant to stabilize San Francisco’s famously leaning and sinking Millennium Tower have now been driven into bedrock, completing the $100 million fix of the luxury condo high-rise, according to the engineer overseeing the project.
On Monday, project engineer Ronald Hamburger said the engineering upgrade to stop the building from tilting and sinking has “succeeded” after the 18 piles were sent 275 feet below the street.
Each pile is designed to support 1 million pounds of weight — which means the new perimeter pile system has shifted a total of 18 million pounds off of the tower’s original foundation, relieving stress on soils that have compressed beneath the building.
Hamburger said the analysis of the foundation shows recovery of nearly 1 inch of tilt following the final load transfer. He said he expects the building will “continue to experience significant recovery of the tilting that has occurred following the final load transfer.”
Millennium Tower, completed in 2009, went from being the city’s poshest condo tower to a symbol of the excesses of the city’s tech gold rush five years later when it was revealed that the building was leaning 24 inches to the west and 7.9 inches to the north.
While the tower’s tilt may have partially been caused by “dewatering” that had taken place during the construction of the Transbay transit terminal next door, most engineers agreed that the piles of the heavy concrete tower’s foundation should have been driven all the way to bedrock.
The work has been overseen by the Department of Building Inspection and an independent panel of experts hired by the city. That panel — the Engineering Design Review Team — was charged with ensuring that the building remained safe for occupancy throughout the construction period, and that the retrofit conformed to the applicable building code requirements and approved construction documents. The tower’s HOA has contracted with a surveyor to monitor the building’s performance over the next decade.
“We will be monitoring it continually for the next 10 years,” said Hamburger.
Millennium Tower Condo Association President Howard Dickstein said he is confident the “engineering upgrade will restore our building’s reputation and the value of condominiums while putting to rest any lingering questions about the Tower’s stability.”
Over the next few months, construction workers will restore the Muni lines, pour new sidewalks and plant new trees — red maples, water gums, and Brisbane boxes — along Fremont and Mission streets. That work will be completed by the end of August.
“As an independent team of engineering experts concluded, this is an effective and practical approach to the settlement and tilting issues, and it preserves and enhances the building’s safety,” Hamburger said. “The fact that the building is responding positively and has stopped settling and is beginning to recover its tilt is very satisfying.”
Hamburger said he doesn’t see any more sinking towers — at least in San Francisco’s Financial District. “San Francisco is pretty much requiring that new buildings in the area go to bedrock,” he said.
Source: San Francisco Chronicle
