Cracks in structural beams forcing the closure of the Salesforce Transit Center originated from where weld access holes were cut into them, a lead investigator said Thursday.
The holes were pinpointed as a likely cause for the cracks in the 4-inch thick steel beams over Fremont Street following analysis of samples tested by a New York lab. The cracks were first noticed in September, a little over one month after the $2.2 billion bus terminal with a rooftop park opened to the public, prompting its indefinite closure.
“Analysis and testing performed, to date, suggests the probable cause of the girder fractures at the [Transbay Transit Center] to be the formation of cracks in the girder weld access hole radi prior to service,” said a report from Robert Vecchio, the president of New York-based lab LPI, Inc.
Vecchio said the beams had weld access holes thermally cut into them, which left behind brittle material full of multiple “micro-cracks.” When the beams were then butt welded there was likely more stress causing the micro-cracks to “pop” into larger cracks that were further exacerbated when installed to hold up the weight of the structure, he said.
The findings are preliminary, Vecchio told the Transbay Joint Powers Authority board of directors Thursday, and “we haven’t arrived at a root cause yet.”
Additional information to come from the investigation is the metallurgical evaluation, which Vecchio said is “just about complete.”
Ed Reiskin, who sits on the board and is also head of the San Francisco Municipal Transportation Agency, asked if the proper protocols were followed under the building codes when making the thermal cuts.
“My understanding is our specifications complied with the code. There are a lot of unanswered questions,” said Mark Zabaneh, TJPA’s executive director.
Robert Hazleton, the president of Herrick Corporation, the company that cut the holes when fabricating the steel beams, said that “the holes, whether we call them access holes or weld termination holes,” were not in the initial design plans but later added “on an approval and a subsequent RFI.”
“The peer review, when they were looking at the design drawings, they wouldn’t have seen the access holes that we are looking at right now,” Hazelton said. Hazelton did not elaborate on why they were added.
Further results of the investigation are expected at the board’s meeting next month. Plans for repairs and a process to inspect the entire facility remain under development and would need approval by a peer review panel.
“While we do not have yet a date to re-open the facility today makes a significant milestone as we begin to identify the cause of this incident and the ultimate repair of the Transit Center that will follow,” Zabaneh said.