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Old Posted Mar 15, 2017, 3:15 AM
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Pedestrian Pedestrian is offline
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Location: San Francisco
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SAN FRANCISCO | Millennium Tower (aka "The Leaning Tower of SF") | 645 FT | 58 FL


As many people know, this modern condominium tower directly across Fremont St from the under-construction Salesforce Tower and immediately next to the under-construction TransBay Transit Center is leaning (currently about 18 inches at its top to the northwest). The building was built in an unusual fashion for this neighborhood and San Francisco in general for such a large structure: It's foundation is a thick reinforced concrete "pad" with 80 ft pilings (bedrock being 200 ft down). Before construction, this method passed muster with the city Building Department as well as hired siesmic and engineering consultants. The lean was first noticed (in spite of reports of cracking and other disturbing phenomena in visible concrete in the parking garage and elsewhere) after the excavation for the TransBay Transit Center was well underway and the homeowners in the building have sued arguing it was the excavation (and its dewatering) that has caused the lean.

Now this:

Millennium Tower's Earthquake Fitness Models May Not Have Been Accurate

Residents of Millennium Tower have one more reason to shake their fists at the sky and/or file another lawsuit as a report comes to light from a structural engineering expert that suggests that the computer models used to test the seismic safety of the design of the tower are now considered outdated and unsophisticated. As NBC Bay Area reports, structural engineer Ronald Hamburger, who was engaged by the developer to re-review the building's seismic safety, said in a January memo that based on new models, some concrete support structures called outriggers ringing the tower in two places are subject to failure in the event of an earthquake.
The outriggers are bands of steel-reinforced concrete that bind the tower's concrete core with its outside walls. Eight of the tower's twelve outriggers are not as seismically sound as they should be, Hamburger says, with the upper group of four nearest the top of the tower about half as resilient as they should be by modern standards.
According to Hamburger, who was asked to answer questions from a city-appointed panel of experts, this does not mean the building is going to collapse in the event of an earthquake, but it does have a high risk of getting red-tagged following such an event, which is worrying for obvious reasons to homeowners in the tower, who up to now have been told that the building was seismically sound despite the widely reported sinking and tilting issues.
As for how strong an earthquake it would have to be to cause the outriggers to fail, that is something that has not yet been determined.
As another structural engineer contacted by NBC Bay Area, Joe Maffei, explains it, "That’s one of the drawbacks of an outrigger design. Outrigger designs are wonderful for wind — you have to be very careful with them for earthquakes" . . . .

Also, here is an earlier piece to catch up those not following this drama:

Berkeley Prof Who Consulted On Sinking SF Tower Blames The Ground, Which He Wasn't Required To Examine
FEB 3, 2017 2:45 PM

A Cal professor who worked as a paid consultant on the Millennium Tower claimed to city supervisors yesterday that an additional expert would have been needed to look at the building's geotechnical complications, such as the bay mud, rather than bedrock, on which the tower rests. Jack Moehle, a structural engineering professor at UC Berkeley, emphasized the limited scope of his work appraising the designs of the $350 million building, whose unexpected sinking and leaning discovered last year have fingers pointing and lawyers filing suit. According to coverage of his testimony by CBS 5, Moehle testified that his job was just to verify that the tower's design met current building codes, not to verify whether those codes were suitable for the specific site of the tower project . . . .
. . . Back in 2006, according to the Business Times, Moehle wrote that "On the basis of my review, it is my opinion that the foundation design is compliant with the principles and requirements of the building code, and that a foundation permit can be issued for this project." He was later subpoenaed to testify, as he did yesterday.
“I’m not saying that the foundation design has been reviewed by me and that I have determined that the foundation is going to work, etc." . . . .
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