Work to fix transit hub girders is under way
Crews prepare the area near two cracked beams
Crews made preparations to brace a damaged section of San Francisco’s new Transbay Transit Center on Thursday, after cracks were discovered this week in two large steel beams over Fremont Street.
Standing on scissor lifts, construction workers peeled off corrugated metal sheeting below the cracked section while crews inside the facility rerouted electrical lines and other utility equipment. The next step is to ease the pressure on the beams that officials say are in danger of failing.
The Transbay Joint Powers Authority, which built and operates the facility, is trying to locate large steel columns to place under the compromised beams. The columns will run through the bus deck onto Fremont Street.
“The current plan is to put the shoring system in the middle of Fremont Street so we can allow traffic to move around both sides,” said Mark Zabaneh, TJPA executive director. He said the plan is still “very tentative.”
TJPA officials had said the transit center and Fremont Street would remain closed at least through next week as work is done to fix the beams. On Thursday, Zabaneh said he hoped to open Fremont by next week, but said it will depend on how quickly the materi-
als arrive at the job site.
Engineers are trying to determine how to brace the structure before coming up with a permanent fix, TJPA spokeswoman Christine Falvey said.
“They’re working on the design right now and working on procuring the materials they’re going to need,” she said. “They want to make sure everything is locally and quickly available.”
The TJPA said the bracing work could begin this weekend.
As the engineers were developing a plan, construction workers removed superficial paneling, light fixtures and electrical equipment, while others began relocating overhead wires that serve Muni buses.
The first step in fixing the cracks — one is described as 2½ feet long and the other slightly smaller — is to brace the 60-foot beams, which run over the third-floor bus bridge, supporting the deck below and the roof park above.
Crews then will attempt to permanently reinforce the cracked beams, so they can remove the bracing and eventually reopen Fremont Street and the transit center.
At the same time, engineers with the TJPA are working to determine what caused the beams to split.
Zabaneh said the failure was likely caused by one of three scenarios: faulty fabrication of the beams, an installation error or a design mistake that placed too much weight on the beams.
The beams run east to west over Fremont Street and are around 5 feet thick on the ends but widen to around 8 feet at the center. The cracks were discovered along each beam’s bottom 4inch flange near welds connecting the center of the beam to a column below.
Another section of the transit center with an identical design spanning First Street has no signs of stress or cracking, Zabaneh said. The cracked beams were fabricated by Herrick Corp. in Stockton, according to the TJPA.
The failing beams were discovered less than a block from the listing Millennium Tower, a 58-story residential building that has sunk 18 inches since opening in 2009. TJPA officials said they do not believe the problems are linked.
The failing beams are among more than 22,000 tons of steel that make up the skeleton of the stylized transit center that was once envisioned as the “Grand Central station of the West.” The $2.2 billion transit hub in the city’s bustling new Transbay District was in the works for two decades before finally opening Aug. 12.
The cracks were not present when the beams were given a final inspection in January 2016 and a fireproof foam coating was added that June.
Workers discovered the first crack Tuesday morning when they spotted a cleft in the fireproof coating while installing a ceiling panel over the bus bridge.
The TJPA later found the beam was split and shut down the entire facility as crews began inspecting the structure. That night, a second crack was discovered in the same spot on a beam running parallel to the first.
The closure has caused a commute nightmare in the area and traffic problems all over the city. The cracks were discovered as an estimated 171,000 people flooded into San Francisco for the annual Dreamforce conference held just blocks away at the Moscone Center.
Mayor London Breed called for a “thorough and transparent investigation” into the cause and severity of the cracks, while asking for a plan to reopen the facility “as soon as it is safe to do so.”