Millennium Tower Faces Further Problems

It is yet to be determined just how strong of an earthquake would result in the outriggers to fail.

SAN FRANCISCO—Residents of the San Francisco Millennium Tower have been advised based on a new report that the computer models used to test the seismic safety of the design of the tower are considered outdated and unsophisticated.

According to structural engineer Ronald Hamburger, who was asked by the developer to re-assess the building’s seismic safety, indicated in a memo in January 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 seismically sound, Hamburger indicated. The upper group of four near the top of the tower, are  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, the assessment 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 a natural hazard. It has not been determined how strong an earthquake would need to be in order for the outriggers to fail.

While other buildings including the nearby Salesforce Tower have drilled 200 feet down to bedrock to support the structure, the Millennium Tower’s developer believed that 80-foot pilings would be sufficient.  The developer, Millennium Partners, maintains that dewatering of the soil for the next-door Transbay Transit Center is to blame for their building’s excessive settlement.

PJ Johnston, a spokesperson for the developer, issued a statement about the new findings stating: “At every step of the way the building has been determined to be safe for occupancy.”