Concrete wall threatening to fall from SF high-rise stabilized

A construction mishap high atop an under-construction skyscraper sent part of San Francisco’s South of Market neighborhood into disarray Wednesday afternoon and evening.

Fear that an unstable 2,000-pound wall of concrete could topple from the high-rise at 33 Tehama St. triggered city officials to evacuate hundreds of people from at least 16 office buildings, close nearby streets and shut down the westbound Interstate 80 exit ramp at Fremont Street, one of the busiest in San Francisco.

But by 9 p.m., Lt. Jonathan Baxter, a spokesman for the San Francisco Fire Department, declared “we are safe.” He said the surrounding streets and highway off-ramp had been reopened. Only Tehama Street between First and Second remained closed. Evacuation orders were also lifted with the exception of 44 Tehama St. across the street from 33 Tehama.

Baxter’s comments capped a chaotic five hours during which time it was feared the construction glitch could cause major structural damage to the buildings below.

Firefighters went door-to-door asking people to leave their buildings immediately. An engineering expert was flown in from Washington state to help develop a plan on how to manage the leaning wall.

“The worst-case scenario is we’re going to have some structural damage to one or more buildings below,” Baxter said shortly after the incident.

Officials with the San Francisco Fire Department initially blamed the emergency on a malfunctioning crane, but they later said a strut supporting a platform in the elevator shaft broke on the 35th floor, sending the platform careening at a 15-degree angle.

A malfunctioning crane threatened to unleash a 2,000 pound concrete slab from the 30th floor of 41 Tehama St., officials said. A malfunctioning crane threatened to unleash a 2,000 pound concrete slab from the 30th floor of 41 Tehama St., officials said. Photo: Video Frame Grab Via KTVU Photo: Video Frame Grab Via KTVU Image 1 of / 22 Caption Close Concrete wall threatening to fall from SF high-rise stabilized 1 / 22 Back to Gallery

That caused a 30-ton machine used for transferring liquid concrete, which was resting on the platform, to lean precariously into the concrete slab, forcing it to lean outward.

Over the course of 3½ hours, construction crews worked to build a new platform beneath the faulty one. Once that happened, and officials inspected the work, the evacuation orders were lifted and the streets reopened.

“We erred on the side of caution,” said Tom Siragusa, an assistant chief for the San Francisco Fire Department, adding that “the building itself is not compromised in any way, shape or form.”

The building is a 35-story residential tower that was expected to begin leasing one- and two-bedroom apartments this year, according to the building’s website. When completed, it is supposed to feature a gym, rooftop solarium, outdoor terrace and retail and art space.

It is being developed by the Hines and Invesco real estate companies, and the contractor is Lendlease, a property development company. Hines is also the co-developer of the nearby Salesforce tower.

Lendlease released a statement attributing the malfunction to a “partial hydraulic failure” and said the “the interior forming system and the concrete placement arm have been secured.”

Workers inside the evacuated office buildings described a chaotic scene as firefighters came in telling them to evacuate.

There were a couple hundred people inside the Galvanize co-working space at Howard and Tehama streets — in the middle of what the Fire Department identified as the “danger zone” — when firefighters came in giving the evacuation order, said Karina Canles, an employee at Galvanize.

Canales said they weren’t told why they had to get out so fast, so the general mood was one of confusion rather than panic.

Officials told her they wouldn’t be able to get back in the building until Thursday morning, she said, as she stood on the corner behind the police tape, waiting for an update.

Christa Reynolds, a yoga teacher, had parked her car on Tehama Street when police started to block the area. Reynolds hurried back to her car before police finished blocking the area because she forgot one important thing: her 14-year-old dog.

“I thought, ‘My car I could do without,’” Reynolds said. “I couldn’t do without him.”

Hundreds of onlookers in business suits milled around the area after the evacuation order. As the hours dragged on, the number of onlookers had dwindled to a few dozen, and by 9 p.m. just a handful of people stood outside a temporary Red Cross station that supplied food and water.

The California Division of Occupational Safety and Health is investigating the incident. There were no known injuries.

Michael Bodley, Sarah Ravani and Emily Green are San Francisco Chronicle staff writers. Email: mbodley@sfchronicle.com, sravani@sfchronicle.com, egreen@sfchronicle.com Twitter: @michael_bodley, @SarRavani, @emilytgreen