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Fix for CA Transit Center Gets Green Light

Monday, January 14, 2019

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Late last week, the Transbay Joint Powers Authority green-lighted the repair of the two fractured beams in San Francisco’s Salesforce Transit Center.

The fix was proposed in December, after initial findings of what caused the problem were released by a third-party lab.

What Happened Originally

On Sept. 25, workers discovered a cracked steel beam in the third-level bus deck of the $2.2 billion Transit Center, just six weeks after the structure opened to the public. The next day, another fissure was found on an adjacent beam.

The beams are part of the support system for the 5.4-acre rooftop garden and park, which includes a 5-foot layer of soil.

Fullmetal2887, CC-BY-SA 4.0, via Wikimedia Commons

Late last week, the Transbay Joint Powers Authority green-lighted the repair of the two fractured beams in San Francisco’s Salesforce Transit Center.

According to the Engineering News-Record, the bottom-flange cracks are near the 8-foot-deep midspan of each shop-welded girder. In the structure, the hanger plate slots through the bottom flange.

General contractors Webcor and Obayashi managed the center’s construction, which lasted from August 2010 to August 2018. The architect was Pelli Clarke Pelli, with Thornton Tomasetti serving as structural engineer.

In early October, the TJPA confirmed that the shoring systems for the cracked sections were complete, making way for technicians to get in to take samples for analysis at LPI. Testing included scanning electronic microscopy, Charpy V toughness tests, Rockwell hardness tests, tensile tests, fractographic analysis and metallographic analysis.

A peer review was also initiated, overseen by regional transportation agency MTC.

Last month, the report from LPI Inc., a metallurgical lab that investigated the issue, concluded that the problem started with weld access holes that were created in the beam during the joining process.

The transit center’s engineer-of-record, Thornton Tomasetti, presented a fix that calls for bolting 20-inch-wide steel cover plates above and below the area around each fractured bottom flange, similar to a “14-foot-long double splint.”

What Now

The independent peer review panel at the time of the suggested said that it was in “general concurrence” with the proposed fix, and on Jan. 10 the authority, confirmed that it is in the process of gathering materials for the approved scheme.

The repair will be made not only to the girders with cracks, but to a pair of identical girders along First Street that have not fractured.

The authority has not released a timetable on the fix yet, but is expected to do so in the coming weeks.

In addition, the peer review panel is slated to review 15,000 documents related to the design and construction of the structure, and LPI is set to present its finite-element analysis to the review panel on Jan. 18.

   

Tagged categories: Health and safety; Maintenance + Renovation; Mass transit; North America; Public Transit; Safety

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