Cracked American steel forced San Francisco to close new $2.2B transit hub

American steel has become a safety issue at San Francisco’s new $2.2-billion transit terminal.

The city says its Transbay Transit Center will remain closed through next week so engineers can inspect and repair multiple cracks in the steel support beams holding up its rooftop garden.

The busy transit hub, which opened last month, was closed on Tuesday afternoon after maintenance workers found a large crack in one of the garden’s steel support beams. The crack measured 2.5 feet (65 centimetres) wide and four inches (10 centimetres) deep, officials said.

Engineers found a second cracked beam on the structure Wednesday, prompting officials to extend the shutdown through all of next week. The disruption created a commuter nightmare on Tuesday and Wednesday.

The Transbay Transit Center opened last month to much fanfare in San Francisco, where it’s been touted as the cornerstone of the city’s transit future. The structure, officially named the Salesforce Transit Center, spans three city blocks and stands five levels tall.

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The transit hub was built by the Transbay Joint Powers Authority, whose representatives said Wednesday they’re still looking into the cause of the cracks. They added that they’re concerned the beams might fall if the issue is left unaddressed.

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“We’re working hard to rectify the situation,” TJPA executive director Mark Zabaneh said. “We’re very disappointed with what happened,” he added.

“We will get to the bottom of this.”

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The steel beams were fabricated in Stockton, Calif., at Herrick Corp., the TJPA said. The steel was produced under a $189 million contract between the TJPA and Skansak USA Civil West in New York, the San Francisco Chronicle reported.

Zabaneh said the steel beams looked suitable in January 2016, and that the problem could be in the fabrication, installation or design of the beams.

Construction experts say it’s exceedingly rare for steel girders that support buildings to crack.

Engineer David Friedman said the beams likely arrived without cracks, but that once the weight of the roof garden and other structures were added, “new stresses may have exacerbated the possible fabrication flaws.”

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The beams likely passed inspection after installation, engineer Joe Maffei told The Associated Press.

“If that’s the case, it’s likely welding caused the problem,” he said.

The bus and train terminal took nearly a decade to build, and has long been touted as the “Grand Central of the West.” It’s expected to accommodate 100,000 passengers each weekday and up to 45 million per year.

American steel has become a sticking point between the United States and Canada. U.S. President Donald Trump imposed tariffs on imported Canadian steel in May, citing a rarely used 1962 law that allows him to do so on the grounds that certain goods threaten national security.

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The U.S. and Canada are currently locked in heated negotiations over a replacement for NAFTA.

The Transbay Transit Center sits next to the Millennium Tower, another troubled San Francisco landmark. The tower, which was built over a former landfill, has settled approximately 18 inches (45 centimetres) since it opened in 2009.

Zabaneh says the two structures’ woes do not appear to be related.