[Pedestrian]

Holes Cut in Steel Beams Led to Cracking at San Francisco's Transbay Terminal: Engineers
By Jaxon Van Derbeken

Published at 6:06 PM PDT on Oct 1, 2018 | Updated at 11:39 PM PDT on Oct 1, 2018

Engineering experts tell NBC Bay Area the cracks found in the Transbay Terminal superstructure appear to have started at the sharp corners of holes cut into vital steel beams during construction – edges long understood to heighten stresses in any steel structure.

“It’s not a good structural element,” says mechanical engineer Bernard Cuzzillo, referring to rectangular notches clearly cut in the four-inch thick steel at the bottom of the 85-foot long I-beam used to support the terminal deck across Fremont Street.

Cuzzillo referred to one of the holes visible in the 2.5 foot wide strip, or flange, where a vertical steel plate is attached to the I-beam. “To have a hole right there creates a weak spot right where the force is greatest,” says Cuzzillo, who studies why such massive structures fail.

In fact, enhanced photos appear to show at least one of the cracks started at one of those sharp-edged corners. Normally, such edges would be rounded to prevent stresses from being concentrated at the corners, the engineers say. It is not clear why the corners were not rounded in the Transbay project or what was their intended purpose . . . .

https://www.nbcbayarea.com/news/loca...494862071.html