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Construction workers have finished opening a big hole under the Transbay Transit Center bus bridge on Friday as off-site crews start making temporary columns that they plan to ship during the weekend. to support two cracked beams.
A team of engineers and manufacturers were hoping to finalize plans for a shoring system early Saturday so that they could start installing the columns "very soon," said Dennis Turchon, senior director of transit center construction.
"We will start seeing temporary supports in the next few days," Turchon said. "We started off-site manufacturing to minimize the on-site process."
The columns will support the damaged girders over the bus bridge and under the roof park of the transit hub. The beams support the entire section of the building that runs through Fremont Street.
Temporary columns will rise from the street through the hole to reinforce the cracked beams. The design will be subject to review by independent third parties before the workers start installing the pillars.
Mr. Turchon does not estimate how much the work would cost, but he said it would be a "significant sum" because a large team of designers and manufacturers are involved in the project.
The workers rerouted Thursday and Friday electrical conduits, plumbing pipes and other utilities to create an opening for the bracing equipment.
"We had a lot of things to take care of and these are essentially eliminated at this point, so it's clear now to proceed with the installation," said Turchon.
The officials of Transbay Joint Powers, who built and operate the plant, hope to reopen Fremont Street by the end of next week. They plan to place the columns in the center of the street so that traffic can move them.
When teams put together the quick fix to avoid a potential collapse, engineers develop a plan to secure bundles over 60 feet long permanently.
Workers discovered the cracks on Tuesday while they were installing ceiling panels. This prompted officials to shut down all the facilities, as well as the section of Fremont Street below, while the engineers were trying to diagnose the problem.
The cracking is isolated on the two beams in the center of the span above Fremont Street, said the executive director of the authority of the powers, Mark Zabaneh. Another part of the building above First Street, which is identical in design to the cracked part, shows no sign of stress or crack, he said.
The cracks extend along the bottom edges of 4 inches thick beams. One crack covers the flange 2½ feet wide, while the other crack covers only part of the flange. The beams are 5 feet thick at their ends and widen to 8 feet in the center, where they are welded to a column attached to the bus deck below. The cracks are a few inches from the welds.
The cause of the problem remains unknown. Engineers believe that cracking is the result of a problem in the fabrication of the beams, an installation error or a failure of the building design.
Mr. Turchon said that the Joint Powers Agency had continued to monitor and test other areas of the structure and no other problem had been found.
The mayor of London Breed has asked for an investigation on cracking. The agency has announced that it will use outside engineers to conduct a peer review of the building design.
The $ 2.2-billion three-block building, located in the center of the new Transbay neighborhood, opened on August 12 after two decades of planning and construction.
Evan Sernoffsky is a writer of the San Francisco Chronicle. Email: [email protected] Twitter: @ IvanSernoffsky
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