EuroWire March 2019

Transatlantic Cable

He also observed that experts disagree on how much grinding is needed to remove micro-cracks formed during welding. Nor is it clear, he said, how much the shape of the access holes contributed to the cracks forming in the beams at the transit centre. These were a “little too granular” to be included in the design drawings, Mr Alameida said, but were available as “shop drawings” of the kind consulted by steel fabricators when they are welding beams together. If those holes had been included in the design drawings they might have been reconfigured or shaped differently to ensure that the beams did not fail, Loring Wyllie, a structural engineer and senior principal at the earthquake engineering company Degenkolb Engineers (San Francisco), told Ms Baldassari. He served on the authority’s structural and seismic peer review panel that convened between 2008 and 2014 to review the design of the building. The shape of the holes is significant, Mr Wyllie said, because it can be a factor in metal stress. The holes in question were rectangular, typically avoided in welding. “You never like sharp edges or notches or things like that when you’re dealing with welds,” he said. “You like them to be nice and smooth and rounded.” ‘Obviously, something was missing’ The TJPA is examining other areas of the building for possibly similar instances of failure, said Dennis Turchon, the agency’s construction manager for the transit centre. A peer review panel convened by the Metropolitan Transportation Commission (MTC), the transportation planning, financing and coordinating agency for the nine-county San Francisco Bay Area, has hired its own consultant, Michigan-based Ruby+Associates, to do a parallel analysis. Mr Turchon said that both teams would sift through some 15,000 pages of documents to identify locations in the building that warrant further investigation. Their report will likely cover the thickness of the steel plates, the type of welds used, and the presence of an access hole, among other factors. † Meanwhile, questions remain about the assignment of blame. And no date has been set for reopening the transit centre, although workers have begun on a fix for the cracked beams. This involves sandwiching steel plates on either side of the girder and bolting them in place. † Mr Zabaneh said that – while, in January, it was still too early to make a judgement – whether or not the quality

Steel

Access holes ‘a little too granular’ to figure in some 21,000 inspection reports are suspect in the cracks in two steel beams that shuttered a $2.2 billion building “Essentially 64,000 times things of concern were addressed and reviewed. It’s an extraordinary amount of oversight.” It is that; but the quality control and assurance procedures referenced by Ron Alameida, the director of project management for the Transbay Joint Powers Authority (TJPA), the public agency in charge of constructing and maintaining the Salesforce Transit Center in San Francisco, apparently were not enough. According to agency officials, the efforts failed to identify issues that led cracks to form in two structural steel beams at the $2.2 billion facility, eight years in the construction. Workers installing ceiling panels spotted the cracks roughly six weeks after the building was opened, in August 2018. It has been closed to the public ever since. A recent update was provided by Erin Baldassari of the Marin Independent Journal , who reported that, as of the New Year, no cause for the cracking had been officially identified, although experts have zeroed in on access holes cut into girders after the beams were welded together. The information that follows is taken from her account of the progress of the TJPA investigation. (“‘Extraordinary’ Oversight failed to Identify Issues With Cracked Steel Beams at SF’s Transbay Terminal,” 10 th January) Robert Vecchio is the president of New York-based LPI Inc, which conducted a series of tests on samples taken from the beams to identify the root cause of the cracks. Mr Vecchio said in December that the heat from torch-cutting the access holes made the steel more susceptible to cracking. Can the shape of a hole be crucial? For his part, Mr Alameida of the TJPA said that the agency’s procedures produced more than 21,000 inspection reports that were subjected to multiple layers of oversight by various entities involved in the building’s construction. The access holes that appear to have contributed to the cracks in the beams were inspected and approved. Mr Alameida said: “It was not missed.”

Image: www.bigstockphoto.com Photographer Adrian Grosu

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March 2019