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Repair work to start on closed £1.6bn transport hub

Engineers are gearing up to design a permanent repair for a cracked steel beam which has forced the closure of a major newly built, $2bn (£1.6bn) transport hub in San Francisco.

The two cracks were discovered on 25 and 26 September in the bottom flange of two 24m long steel beams which support the roof slab on the eastern side of the building.

The three-storey, 450m long, 50m wide transport hub has a bus deck on its second floor and a 2.2ha public park on its roof. In a future phase of development, the basement of the building will also house the northern terminus for California’s High-Speed Rail system.

After the cracks were discovered, the building, which had opened only six weeks before, was closed and a “multi-level shoring system” was installed to provide alternative support to deck above.

In a November update report, owner and operater of the building, the Transbay Joint Powers Authority (TJPA) said samples taken from the  cracked steel beams were undergoing testing at a metallurgical laboratory to determine the cause of the fissures.

Test results are expected by the end of the month, after which, it said an additional review of the results by independent experts would occur.

The report says that the results of the tests will determine the cause of the failure and allow the TJPA to design an appropriate permanent repair. Planning for repairs is due to start next week.

The tests include a scanning electronic microscopy, a Charpy V notch toughness test, several tensile tests and metallographic analyses.

The building was designed by architect Pelli Clarke Pelli and structural engineer Thornton Tomasetti and built by WebcorObayashi joint venture. 

The building has been built so the structure can survive “maximum” earthquake shaking without major structural damage or significant loss of function.

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