SFO's Leaning Tower Tips Two More Inches Since January

July 21, 2017

San Francisco's Millennium Tower on Mission Street is still sinking and tilting, despite efforts to stop the building's settling.  

Amidst various claims, blames and lawsuits between the developer, Millennium Partners, city attorneys, condo owners and the building's homeowners association, the general consensus is that the 58-story tower sits on the wrong type of foundation. The result has been the tower has sunk at least 17 inches and is off vertical center by 14 inches. There have also been reports of water leaks and damage in the parking garage, damage to interior finishes in some apartments, and cracked sidewalks due to the tilt. Nearby buildings are nervous.

The Arup engineering firm reported the new measurements this week, after which Millennium Partners said neighboring projects – Transbay Transit Center and the Salesforce Tower – are “de-watering” the ground and undermining Millennium’s Tower’s foundations. Millennium Partners has long maintained underground construction near their tower is the cause of the tilt.

Tax relief for some

More than 160 owners of Millennium Tower condominiums have appealed to tax authorities, saying the value of their $1 million-plus properties have plummeted, in some cases to as little as 0$.

On Tuesday a group of 50 owners appealed to the city to waive their property taxes for 2016. Monday,  City Assessor Carmen Chu ruled that 99 of the 160 owners would receive an average $3,000 reduction on their 2017 taxes. However, that left three-quarters of the owners with no tax break.

Chu explained that for the 99 owners, the average condo value dropped $300,000 per unit. But because many units have tax valuations that are so far below current market value that they are not entitled to relief.

Heaviest building ever built in SFO

The tower is supported by a mat foundation resting on 950 piles, weighing 130 tons each, reaching to a depth of around 80 feet of clay dredged from the bay.

Because the building is made of reinforced concrete rather than steel, the 645-foot tower is also the heaviest building ever built in San Francisco by pounds per square foot according to its engineers, DeSimone Consulting Engineers.

In a summary of a paper submitted by the engineering firm before the tower was completed, it says " The tower's immense height posed many challenges and required the creative use of technologies and cutting edge innovations. The tower's dual lateral system is comprised of a 36-inch-thick concrete shear wall core and partial perimeter Special Moment Resisting Frames (SMRF). Outrigger trusses connect the interior core with robust perimeter super-columns at three intermediate levels to control lateral deflections. In order to reduce the required floor-to-floor heights, shallow steel link beams are used within the shear wall core as coupling beams, in lieu of deeper diagonally reinforced concrete beams. Closely spaced ties in columns and walls posed a challenge to the placement of the high strength 10 ksi concrete needed for this project. To alleviate some of this congestion, DeSimone specified a system of Welded Reinforcement Grid (WRG) that eliminated all hooks, significantly reduced the volume of rebar, and decreased overall labor costs."

DeSimone has proposed drilling 50 to 100 new piles down into bedrock to stablize the building at a cost of $150 million.