Since the problem was originally identified in 2016, San Francisco’s Millennium Tower has been slowly but surely sinking and tilting westward towards the adjacent Mission Street. While Handel Architects, DeSimone Consulting Engineers, and the developer Millennium Partners contend that the execution and design of the project were sound, with the current structural issues stemming from the construction of the similarly defective Transbay Transit Center nearby, one fact remains clear: the tower must be stabilized to halt its sinking. Today, the developers and structural engineering firm Simpson Gumpertz & Heger have submitted a $100 million proposal to retrofit the tower with a new system of piles reaching the bedrock below. Currently, the tower rests atop a 10-foot-thick concrete foundation bonded by nearly 1000 reinforced concrete piles driven close to 90 feet into a layer of soft clay that stretches across the Bay Area. While this practice is not uncommon in Downtown San Francisco, the sheer mass of the city’s fourth tallest tower places substantial strain on the soil below. The stabilization plan, led by Senior Principal Ronald Hamburger of Simpson Gumpertz & Heger, consists of approximately 50 new steel-and-concrete piles drilled 250-feet into the bedrock below. According to The San Francisco Chronicle, “each pile is 24 inches in diameter and weighs 140,000 pounds and would take three to four days to drill into place,” with a “reinforced concrete inner pile installed within each steel shaft.” How will this new ring of piles address the tower’s sinking? According to the Millennium Towers Homeowners Association, the “Perimeter Pile Upgrade” will reduce compression placed on the clay soils along the north and west elevations whilst encouraging secondary compression and two to three inches of sinking on the east and south elevations. This plan will effectively reduce, but not eliminate, the building's 14-inch tilt while prospectively stabilizing the entire foundation. The Perimeter plan is “an effective and practical approach to the settlement and tilting issues,” said Hamburger, which “preserves and enhances the building’s safety.” If the city approves the permit application, construction could be completed within 18 months.
Posts tagged with "Transbay Transit Center":
The Transbay Joint Powers Authority (TJPA) board of directors has called for a complete structural evaluation of the Pelli Clarke Pelli–designed Transbay Transit Center in San Francisco after installation crews discovered failing steel structural beams there in September. Now, over a month later, the transit center has been closed for longer than it was open as crews work to discover what went wrong. This week, representatives from TJPA, structural engineer Thornton Tomasetti, contractor Webcor/Obayashi Joint Venture, steel fabricator Herrick Corporation, and material supplier ArcelorMittal are all convening in New York to study material samples that were removed from the failing girders for further analysis. Engineering News Record reported that crews discovered bottom-flange cracks near the midpoint of one of the eight-foot-deep shop-welded girders. A second, more serious fracture was discovered running the entirety of a flange on the second beam. The two beams run parallel to one another over an 80-foot span running over Fremont Street. At a recent meeting, the TJPA board called for a complete structural evaluation of the 1.2 million-square-foot transit center in order to inspire public confidence in the structure’s safety and design. Ultimately, however, TJPA officials currently have no idea why the beams failed and because the fissures were discovered by accident, it is unknown if other areas are prone to fail, as well. At the meeting, one TJPA board member asked, “Was the engineering done right?" before adding, “We need assurance." The structural review team will now work to understand what happened before making design recommendations for how to fix the problem. Once a consensus is reached regarding on the cause of the girder failures, engineers will design a permanent fix that will also be peer reviewed to ensure its safety, Engineering News Record reported. TJPA projects that repairs will begin in December and take several months to complete.
A second cracked steel structural beam was discovered at the Salesforce Transit Center in San Francisco Wednesday during an overnight examination, The San Francisco Chronicle reports. AN reported the initial cracked beam Tuesday afternoon. The Chronicle reports that the initial fissure discovered in a steel structural beam supporting the transit center’s 5.4-acre, PWP Landscape Architecture–designed park measures roughly 2-1/2 feet long by four inches deep and runs across the bottom of a 60-foot-long spanning element located above Fremont Street between Mission and Howard Streets on the transit center’s east side. The second damaged steel beam that was discovered runs parallel to that element and features a crack that is "slightly smaller," according to the report. As a result of the escalating situation, the transit center will remain closed at least through October 5 as crews work to investigate other elements of the structure, according to the Transbay Joint Powers Authority (TJPA), the entity that oversees the transit center and managed its construction. Pelli Clarke Pelli Architects designed the terminal as well as the Salesforce Tower located next door. During a news conference Wednesday afternoon, Mark Zabaneh, executive director of the TJPA, said, “We will not open the transit center or Fremont Street until we are certain the issue is 100 percent rectified.” Officials at TJPA are worried the structural elements might fail and are therefore operating with a high degree of caution with regards to keeping the transit center closed. The steel beams in question were fabricated in Stockton, California, by Herrick Corp. as part of a $189-million contract struck between Skanska USA Civil West of New York and TJPA. TJPA authorities are inspecting the structure with the project contractors—Webcor and Obayashi entered into a joint venture for the job—and structural engineering firm Thornton Tomasetti, which was the engineer of record for the structure and also performed construction work on the building. Those authorities also plan to bring in independent engineers to reassess the facility’s design. AN will continue to report on this story as it develops.
Millennium Partners, the developer of Handel Architects—designed Millennium Tower in San Francisco, is being taken to court over the building's alarming sinking issue. The tower's homeowners association (HOA) let residents know last Thursday that it was filing a case against both Millennium Partners and Transbay Joint Powers Authority—the firm behind the substantial transit development adjacent to the tower. In the months prior to this, the HOA had staved off any legal action, advising tenants to do the same, as they privately discussed workarounds with the developer. (Some residents still filed lawsuits of their own.) During this process, the finger of blame was pointed toward the $2 billion, Pelli Clarke Pelli–designed transit scheme nearby that reportedly destabilized the tower's foundations. The 20 tenants that took matters into their own hands, though, made a different case. They argued that Millennium Partners was well aware that the structure had sunk significantly more—and at a faster rate—than expected, and failed to let prospective buyers know. A study in Fall of last year found that the tower and sunk 16 inches since it’s opening in 2008. By contrast, initial predictions for the building suggested that it would only sink six inches over its lifetime. To make matters worse, Millennium Tower is not settling evenly either, something which has result in a two-inch tilt. According to coverage from NBC Bay Area, the HOA has said: "The lawsuit would be intended to ... hold the defendants responsible for the damage to the building and... require the defendants to fund a comprehensive repair and restoration of the building, among other relief." A meeting scheduled for March 6 will apparently be held to "to discuss problems that may lead to the filing of a civil action, nonlitigation options, and other considerations." Whether the residents, unlike their tower, settle, remains to be seen.
The tallest residential tower in San Francisco, and the city's third tallest overall, has sunk 16 inches since it's opening in 2008, according to SFGate. Designed by Handel Architects, the Millennium Tower is one of the highest-profile buildings in the city with units selling as high as $12 million for a penthouse, one of which was owned by venture capitalist Thomas Perkins until his death earlier this year. Other notable residents include San Francisco Giants outfielder Hunter Pence and former 49ers quarterback Joe Montana. Currently the Transbay Transit Center, a transit station and neighborhood development project, is under construction on an adjacent site. Its first phase is due to be completed in late 2017, but a study of the site conducted by Arup in 2010 found that the tower had already sunk ten inches. Initial predictions for the tower suggested that it would only sink six inches over its lifetime. Of added concern is the fact that the tower is not settling evenly, and now has a tilt of two inches. Professor Greg Deierlein of the John A. Blume Earthquake Engineering Center at Stanford University told SFGate that these figures were "significant...and of concern," but not yet a threat to safety. However, the imbalance can lead to expensive maintenance costs down the road due to cracking walls and other structural issues. The Transbay Transit Center and the building's developer, Millennium Partners, have each placed blame for the tilt on the other. P.J. Johnson, a spokesperson for Millennium Partners, told SFGate that the nearby construction on the Transit Center caused the problem, suggesting that adequate measures were not taken to protect the tower during the excavation. Representatives of the Transit Center, on the other hand, have suggested that Millennium engineers cut costs and failed to anchor the building into the bedrock. The building also uses concrete rather than steel, and is therefore much heavier. It's unclear what steps developers will take to combat the issue, but it will likely involve expensive and complicated repairs.
New York has one, Chicago has one, and now the Chronicle’s John King alerts us that San Francisco might see a Trump-brand tower in its future. No one is taking bets on the conservative presidential candidate’s name emblazoned on a highrise located in one the most progressive cities on the planet, but King is stirring the pot to call attention to a land auction hosted by Transbay Joint Powers Authority on September 2. On the docket: a parcel of land on the 500 block of Howard Street, where zoning allows for an 800-foot tower. Five development teams will bid against each other. According to King, “[I]dentities are being kept secret until the live auction to, in the words of bureaucrats, 'preserve the integrity of the competition.'” Will Trump be one? The Chron’s critic is wagering a guess, suggesting that with minimum bid at $160 million, the live auction could set off a bidding war that would help pay for the Transbay Transit Center. Designed by Pelli Clarke Pelli, the center expected to serve eleven different transportation systems and feature a rooftop park. The tower on the offer would join others in San Francisco's Transbay district by Studio Gang, OMA, SOM, and Foster and Partners. Gang’s undulating 40-story tower recently came under fire for its soaring height, which community activists protested would cast a shadow over the public Rincon Park on the Embarcadero waterfront. King’s argument, however, is not that Trump will soon be mixing it up in the town of Milk and Moscone (or the new SF: Twitter and Uber) but that design is pushed off the table for the sake of raising cash. In 2007, the city held a design competition for the transit center and neighboring tower. This auction comes with no design strings attached. “Standards are slipping,” he wrote and continued: “If the check clears, good enough. Let the city’s Planning Department sort through messy questions about how the tower looks or whether the developer will try to push for extra space.”