Friday, December 14, 2018

Up, up, and away

Onward the path of science: Holes cut into steel contributed to beams cracking at SF’s Salesforce Transit Center.

Who do you get to look at your damaged steel beams? Well, how about Robert Vecchio?

Dr. Vecchio is a licensed professional engineer in New York, Massachusetts, Kansas, Washington, and Florida, and holds a B.S. in Aerospace Engineering and Supplement in Materials Science from University of Southern California, an M.S. in Metallurgical Engineering from Lehigh University, an M.S. in Civil-Structural Engineering from Manhattan College, and a Ph.D. in Metallurgical Engineering from Lehigh University. He was recently named a Fellow of ASME.

Over the past three decades, Dr. Vecchio has participated in some of the most challenging structure and system issues including the Exxon Valdez Hull Rupture, 1993 World Trade Center bombing, the Hell Gate gas main and Gramercy Park steam main explosions, the 4 Times Square scaffolding collapse, Indian Point NPP steam generator girth weld cracking, ACELA train brake failure and redesign, I-35 Minneapolis bridge collapse, FFS assessment of New World Trade Center Transportation Hub, and the tragic rescue and recovery efforts following the collapse of the World Trade Center towers.

That's quite the C.V.!

The Mercury News reports on Dr. Vecchio's findings:

Defects that occurred during fabrication, along with holes cut into the steel, are likely what caused two structural steel beams to crack just six weeks after the $2.2 billion Salesforce Transit Center opened to the public, officials said Thursday.

“It occurred very rapidly, and a lot of energy was released,” said Robert Vecchio, the president of New York-based LPI, Inc., which conducted a series of tests on samples taken from the steel.

The center closed in September after workers found the first crack in a four-inch-thick steel beam while installing ceiling panels. Authorities closed the center several hours later out of an “abundance of caution,” they said. A subsequent investigation revealed the second crack in an adjacent beam, both of which are in a section of the building above Fremont Street.

The cracks originated in an area where crews had cut “weld access” or “weld termination” holes. It’s unclear which type of hole the fabricators cut into the steel because they are not drawn into the shop designs.

NBC News has a slightly different take: Transbay Transit Terminal Reopening Uncertain as Engineers Continue to Examine Cracks in Critical Beams:

The cracks in critical beams that shut down the Salesforce Transbay transit terminal started at the rough edges of holes ordered cut in the four-inch thick steel during fabrication, a New York-based engineer told the project’s governing board Thursday.

NBC Bay Area’s Investigative Unit first reported the problems with the so-called weld access holes that crews using welding torches cut into the now cracked beams that support the terminal across Fremont Street. Engineers pointed to the corners of those holes as under particular stress.

The expert who is overseeing the testing and analysis of the cracks, Robert Vecchio of LPI Inc., said the cracks began with “a pre-existing defect that occurred during the fabrication.” He said the investigation showed tiny cracks in every sample they looked at. Cracks that “popped out” under stress. “We found these small cracks throughout all the sections that were removed from the girders.”

When the holes were cut with torches, he said, workers left behind rough surfaces. Such rough areas should be ground smooth under building codes.

The subcontractor that fabricated the beams adds more detail, or, perhaps more confusion, to the picture. NBC News reports:

Robert Hazleton, president of The Herrick Corporation, the firm that fabricated the beams, spoke after the meeting. He said the cuts were not called for in the original design plans and in some cases were cut into the structures after they were already built – so they didn’t actually serve as weld access holes as defined by code. Documents show confusion about their purpose, location and specification.

While the Merc adds more background:

Weld access holes allow workers access to the beam so they can complete the weld, said Ashwani Dhalwala, a principal of AEC Solutions who has worked extensively on the issue of fractures in steel. Weld termination holes are used in areas where girders are joined together with a perpendicular piece of steel, called the web, in order to reduce stress, which is concentrated where the pieces interest. It’s a way to provide continuity between the pieces and reduce stress, he said.

“If you have a sudden discontinuity, then you have very high stressors,” Dhalwala said.

The holes were added after shop designs were submitted for approval. So, Herrick crews first built a set of girders without the holes and then had to build a new set of girders with them included, he said.

“Why they were added, that’s more of a design issue than a fabrication issue,” Hazleton said. A representative from Thornton Tomasetti, the design firm, declined to explain the purpose of the holes.

Confused yet?

I sure am.

But it seems like the takeaway, for now, is this:

But, the Transbay Joint Powers Authority, the public agency in charge of building and maintaining the terminal, expects to have a plan for the repairs and an estimated reopening date in January, said Mark Zabaneh, the authority’s executive director. That plan will include bolting steel plates onto both sides of the girder to reinforce it.

I'm pretty sure we're supposed to read that as: "a plan ... in January," NOT as: "a plan ... and ... reopening ... in January."

But what do I know?

I'm just a software guy; bolting steel plates onto things is a long way from my bailiwick.

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