US cracked steel has forced San Francisco to close its new $ 2.2 billion transit center – National

US steel has become a security issue in San Francisco's $ 2.2 billion transit terminal.

The city said its Transbay transit center will be shut down next week so engineers can inspect and repair the multiple cracks in the steel support beams that support its rooftop garden.

The busy transit center, which opened last month, was closed Tuesday afternoon. The crack had a width of 2.5 feet (65 centimeters) and a depth of four inches (10 centimeters), said officials.

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The engineers found a second cracked beam on the structure on Wednesday, prompting officials to extend the closure of the whole of next week. The disturbance created a suburban nightmare on Tuesday and Wednesday.

The Transbay Transit Center was inaugurated last month in San Francisco, where it was touted as the cornerstone of the city's transit future. The structure, officially called the Salesforce Transit Center, spans three blocks and has five levels.

The transit platform was built by the authority of Transbay Joint Powers, whose representatives said Wednesday they were still examining the cause of the cracks. They added that they feared that the beams would fall off if the problem is not resolved.

"We are working hard to rectify the situation," said TJPA Executive Director Mark Zabaneh. "We are very disappointed with what happened," he added.

"We will get to the bottom of things."

The steel girders were manufactured in Stockton, California, at Herrick Corp., said the TJPA. The steel was produced as part of 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 appropriate in January 2016 and that the problem could be the fabrication, installation or design of the beams.

Construction experts say that it is extremely rare for steel beams to support buildings.

Engineer David Friedman said that the beams probably arrived without cracks, but that once the weight of the roof garden and other structures added, "new constraints could have exacerbated possible manufacturing defects." ".

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The beams probably passed the inspection after installation, said engineer Joe Maffei at the Associated Press.

"If so, it is likely that the welding caused the problem," he said.

It took nearly a decade to build the bus and train terminal, which has long been referred to as "Grand Central of the West". It is expected to seat 100,000 passengers every day of the week and up to 45 million a year.

US steel has become a point of friction between the United States and Canada. The President of the United States, 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 United States and Canada are currently engaged in heated negotiations on the replacement of NAFTA.

The Transbay Transit Center is located next to the Millennium Tower, another troubled San Francisco landmark. The tower, which was built on a former landfill site, is about 45 centimeters from its opening in 2009.

Zabaneh says that the misfortunes of the two structures do not seem to be related.