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Thousands of people were evacuated from the SEG Plaza in Shenzhen on May 18 when the building began to sway. Two months later investigators say they have an explanation and a plan to fix the problem. Photo: Weibo

Chinese investigators announce cause of mysterious shaking in Shenzhen’s SEG Plaza

  • Planned work includes removing antennas and repairing damage – but plaza will no longer be among Shenzhen’s 10 tallest buildings
  • Property agent says the landlord may have to offer substantially discounted rent to get tenants back and restore confidence
Shenzhen
The main cause of mysterious shaking in the SEG Plaza in Shenzhen two months ago was a “vortex-induced resonance” from two long masts on top of the building, say investigators.

They said that while the building was safe overall, necessary rectification work – including removing the long antennas and repairing “damage accumulated” over the past two decades – was expected to take over a month, according to a statement on Thursday.

The 350-metre (1,150-feet) landmark skyscraper in the Huaqiangbei electronics district began swaying on the afternoon of May 18, prompting authorities to evacuate thousands of people from the building. It was closed for safety inspections after more tremors were reported in the following days.

After two months of testing, investigators have ruled out potential factors such as the subway running below the plaza, vibration caused by air-conditioning units and nearby construction projects, the statement said.

“The perceived vibration of the SEG Plaza building is caused by a combination of vortex-induced resonance of the rooftop masts and changes to the dynamic characteristics of the building,” it said.

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Investigators conducted 63 vibration tests which showed that when the masts vibrated at a frequency of 2.12 Hz, “bending and torsion vibration” of the building occurred, the statement said.

The team of experts said the building had suffered “accumulative damage” over the past two decades, especially on floors connected to the rooftop masts. However, they stressed that such damage did not affect the building’s overall safety.

Based on the findings, a rectification plan has been proposed that includes removing the rooftop masts and repairing damaged areas.

After removing the masts, the SEG Plaza, currently the fifth tallest building in Shenzhen, will be reduced to 292 metres and will no longer be among the city’s 10 tallest skyscrapers.

A spokesperson for Futian district, where the building is located, said the government would continue to provide temporary space for affected tenants.

“The tenants will be allowed to return to their offices or shops as soon as the rooftop masts are removed and the necessary repair work is completed,” he said.

An electronics wholesaler surnamed Wu, who moved out in late May, said he was glad the problem was being fixed but he had already found a permanent space in another building that was a “better long-term solution”.

“I think government investigators have worked very hard on this but, personally, I think no one can guarantee that it can be fixed 100 per cent. I just want to avoid disruption to my business again,” said Wu, who sells selfie ring lights and other live-streaming equipment.

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A Centaline property agent in Shenzhen said she was not “optimistic” the SEG Plaza could recover its losses unless the landlord substantially reduced the rents.

“It’s not difficult for tenants to find somewhere else [in Shenzhen]. The owner will have to offer steep discounts in order to encourage tenants to stay,” said the agent, who declined to give her name.

“How many will stay even if the landlord cuts the rent by half?” she asked. “Judging from experience, I think not a lot will stay. It will take a long time to restore confidence.”

Ulrich Kirchhoff, associate professor of practice at the University of Hong Kong faculty of architecture, said the government report “may be right to assume that the safety of the main structure is sound” since the vibration of the tower was a one-off-incident.

But he remains concerned about the rapid construction of the building after mainland media reported that the building was rushed at a rate of 2.7 days per floor.

“Potentially, the quality of the building has suffered due to fast-track construction,” he said. ”Furthermore, I don’t think that people will trust the integrity of the building anymore. The psychological damage may be more severe than the actual physical condition. I believe that they will redevelop the site just because of that.”

This article appeared in the South China Morning Post print edition as: Long masts linked to shakes at Shenzhen building
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