Investigators in the southern Chinese city of Shenzhen have turned to vibration simulations to identify the cause of the mysterious trembling that shook the SEG Plaza, after a nearly two-week probe failed to explain it conclusively.
While waiting for the official verdict, hundreds of shop owners housed in SEG Plaza – a skyscraper over 350 metres (1,150 feet) tall and known as the go-to place for electronics products in Shenzhen – must cope with the double blow of expensive rent and lost sales after they were forced to move out of the swaying building two weeks ago.
The Shenzhen government said on Monday its investigators would carry out new tests, including “vibration-excitation” to identify the cause of the trembling.
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Vibration-excitation tests usually involve generators to simulate different vibration patterns to test a building’s integrity and identify parts causing resonance or that are the structural weak points.
“In principle, such tests may cause vibrations but will not affect the safety of the building structure,” the government said, stressing that key safety parameters remained “normal”.
The order to conduct further tests came after the tallest electronics shopping centre in China’s Silicon Valley in southern Guangdong province had a series of shaking episodes resulting in a mass emergency evacuation and the closure of the building.
On May 25, two days after Guangdong Communist Party secretary Li Xi ordered a swift and “scientific” investigation of the SEG Plaza, the investigators said the overall structure of the building “meets requirements”.
A Shenzhen civil engineer involved in the safety inspection told the South China Morning Post the official conclusion might take “quite a while”, as the test process would be tedious.
“It is very hard to commit to a deadline. Basically, we need to install mechanical vibrators, which can generate different vibration patterns so we can run tests on the major structures,” he said, requesting to comment under anonymity as he was not authorised to speak to the media.
“There are more than 70 floors. It is going to take quite a long while to run an exhaustive test. We are very careful here as we need to sign off on the final report and that is a huge responsibility.”
Ulrich Kirchhoff, associate professor of practice at the University of Hong Kong faculty of architecture, said Shenzhen government’s ambient vibration test or excitation test was to confirm whether the shaking episodes were a one-time “freak incident” or if there were some “long-term dynamic processes in the building that can lead in the worst case to a collapse”.
“The shaking of the tower is puzzling indeed. On that day of the incident there was not any typhoon, nor an earthquake. According to the initial investigation there is no damage to the structure … These tests ensure that no ambient or environmental force cause any structural effects in the building,” Kirchhoff said.
Kirchhoff said the usual culprits for quality problems in skyscrapers were fast-track construction, a staggered design process – when construction starts while the architect is still designing – and the use of cheaper and inferior materials.
“In a fast-track construction, the speed of floor-to-floor construction is rapid. In Hong Kong we take around five days per floor, four days with precast units,” he said. Mainland media reports the SEG Plaza was built at a rate of 2.7 days per floor.
He said that in Hong Kong, statutory processes and building regulations had been honed by experience to make buildings safer.
“In this city, the approval process of a building is very complex, procedural and rigorous for each stage of planning and construction,” Kirchhoff said.
“As an example, one of my projects, ‘Upper Central’ in Caine Road is a very slender pencil tower. We had to engage a professional wind tunnel testing facility to proof the integrity of the structural calculations.
“Even though the structural calculations were made with a computer, a live test with physical model can simulate the environmental forces in relation to topography and surrounding buildings very accurately. Even after testing, some structural members had to increase in size while others could be reduced.”
Meanwhile, hundreds of affected SEG Plaza shop and office owners have moved to nearby vacant premises in the Huaqiang north district.
An electronic goods wholesaler surnamed Wu said he had rented a nearby shop on a day-by-day arrangement to keep the business going, but his sales dropped “more than half”, from daily sales of over 2,000 selfie ring lights and other equipment to live-streaming hosts.
“The walk-in customers are almost all gone and online sales also dropped as people thought we closed for business after the SEG Plaza closure,” he said. “I am not the only one. In our group chats, many complained about similar things.”
He said commercial rent had risen with growing demand by more tenants from SEG Plaza seeking a temporary space.
“It’s a headache. I am doing more online promotion now and talking to past customers, telling them that we are still open. I just hope the experts can fix the building and announce that it is safe so we can move back in.”
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