Source:
https://scmp.com/news/hong-kong/transport/article/2182423/hung-hom-station-remains-safe-despite-defective-platform
Hong Kong/ Transport

Hung Hom station remains safe despite defective platform steel bars, engineering expert says

  • Chartered civil engineer Nick Southward tells inquiry that structural safety not threatened, but HKU professor says otherwise
The Sha Tin-Central Link is Hong Kong’s most costly rail project to date. Photo: Dickson Lee

Hong Kong’s Hung Hom station remains safe despite investigators finding 40 per cent of steel bar connections on new platforms defective, an engineering expert told an inquiry into a construction scandal on Wednesday.

But another expert countered that view by insisting the structural integrity of the building had been called into question.

Chartered civil engineer Nick Southward, executive director of Tony Gee and Partners, offered an upbeat assessment for the commission of inquiry into shoddy building work that has plagued the HK$97.1 billion (US$12.4 billion) Sha Tin-Central Link, Hong Kong’s most costly rail project to date.

Leighton Contractors (Asia), the main engineering firm on the job, is embroiled in allegations that reinforcement bars were cut short to fake proper installation into couplers on platforms, and that supporting diaphragm walls were changed without authorisation.

Allegations have been made that reinforcement bars were cut short to fake proper installation into couplers. Photo: Dickson Lee
Allegations have been made that reinforcement bars were cut short to fake proper installation into couplers. Photo: Dickson Lee

“I can cut to the chase and advise that in my opinion the structure is safe,” Southward said.

A number of bars were found not screwed properly into their couplers, but Southward argued that only about 60 per cent of the full embedment length of a bar had to be screwed in to maintain the safety of the station structure.

“It’s wrong to suggest that the entire threaded end of a rebar must be screwed into a coupler with no visible threads outside,” he said.

Southward explained that according to supplier BOSA Technology, about 8mm could be left exposed and still count as proper installation.

About 26mm of the threaded section of a bar should be inserted to maintain structural safety, he believed. Based on this benchmark, Southward said 97 per cent of the bars on two platforms were satisfactory as only two out of 75 samples checked so far did not comply.

“The tests show that 97 per cent of the couplers can carry the design load. We can be very confident that ... the structure will remain adequate and will be safe,” he said.

However, the government has adopted a higher benchmark of 37mm in arriving at its assessment that 41 per cent of the installations were substandard. As of Wednesday 83 bars had been inspected.

But Southward said: “The structure will remain safe and suitable for use.”

He also asserted that the changes to the top of two diaphragm walls were better than the original design and produced a stronger and more robust structure.

However, Dr Albert Yeung Tak-cheong, associate professor at the University of Hong Kong’s department of civil engineering, insisted a minimum of 40mm was necessary to ensure station safety.

He said a 60 per cent substandard rate would result from this benchmark.

“I would say I have doubts about the structural integrity of the station,” Yeung said.

The hearing continues.