San Francisco's Millennium Tower will continue to sink

- The Millennium Tower looks like it will keep sinking but, no one knows for how long or how much. Alarmed homeowners are doing what they can but an internationally renowned earthquake engineer says buildings that settle way more than expected are tough to fix at best.

Drilling crews began installing sophisticated sensor systems at three locations around the 645 foot high, 58-story Millennium Tower in San Francisco's South of Market skyscraper forest.    

The crews are working for the homeowner's association, the only body that can sue to recoup money to fix the building in its entirety. They want to find how much more this building will sink beyond the current 16 inches.

"So, you might get a better idea how long it's gonna take to settle, how much it's gonna settle, that sort of thing," says investigative engineer Patrick Shires of Cotton Shires Engineers & Geologists.

The sensors will measure underground water pressures, ground movements as well as compression of the sands, muds and soils the building sits atop. This will help determine what really needs to be fixed and, just as importantly, who will be financially responsible for what can only be enormous costs.

"Mainly what we're looking at now is what we can do to mitigate the problem," says Mr. Shires.

That may be a very tall order. I spoke with Peter Yanev, a premier San Francisco earthquake engineer. Yanev is in no way involved with the Millennium Tower. However, he's learned much in almost five decades of designing buildings and investigating how buildings perform in major earthquakes.

He says really large settlements of more than 3 to 6 inches, only happen after buildings have sustained major earthquakes; not before.

"It is extremely unusual to be talking about very large buildings settling large amounts; over a foot," says Mr. Yanev.

Huge pre-earthquake tilting and settling are usually due to human error.

"Either construction errors, or inadequate engineering or inadequate codes," says Yanev. That’s not to mention potential repairs, righting and stabilizing such damaged buildings.  I am simply unaware of, you know, a 50-story or taller building being stabilized or repaired after a very significant settlement." says engineer Yanev.
With that said in general, there is no sugar coating the damage this building and its inhabitants are experiencing.

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