The Transbay Joint Powers Authority announced on Oct. 10 that emergency remedial work at the 4.5-block-long Salesforce Transit Center in San Francisco, on the closed Fremont Street between Howard and Mission streets, will continue into early next week. The block, which crosses under the hub, will reopen to traffic and the public on Wednesday, Oct. 17, rather than Oct. 12, as previously announced, says TJPA. The transit center itself, which opened in August, is temporarily closed.
A four-level shoring system is needed to relieve loads on twin tapered built-up plate girders that span 80 ft over Fremont Street. The parallel welded girders have cracks in their bottom flanges.
The girders support the 5.4-acre public rooftop park and second-level bus deck, via hangers.
Towers at the street level of four-level tower-and-beam system on Fremont Street are complete. Work on the second-level bus deck shoring and in the two levels of the train box below grade continues.
Robust Shoring System
“It is important that we have an extremely robust shoring system to ensure that all levels of the transit center are safe and secure. Unfortunately, this requires us to keep the street closed until this work is complete. We will reopen Fremont Street as soon as safely possible and apologize for the ongoing impact to the public,” said Mark Zabaneh, TJPA's executive director, in a statement.
A similar system of twin parallel girders also spans First Street. Though there are no cracks in the First Street system, TJPA is installing shoring there, to be on the safe side. The towers that sit on First Street are installed. Work has been ongoing at night, when the street is closed.
There will be one more night-time closure, between 9 pm and 5 am, next week, on a date to be determined, says TJPA. Thornton Tomasetti, the hub's structural engineer, is currently working on the design of a permanent fix for the Fremont Street girders. First Street girders will ultimately be similarly reinforced.
The cause of the cracks is still under investigation.