Roof collapse at City University in Hong Kong blamed on wrong loading data
Professor Kuo Way releases 18-page document from investigation committee
The roof that collapsed at City University injuring three people last month was probably overloaded because of contractors relying on inaccurate and outdated data to add green features, an investigation committee has found.
The committee released an 18-page report yesterday, redacting some parts due to privacy and legal concerns, recommending legal action against the contractor responsible and calling for three senior campus staff to be disciplined, as reported exclusively by the Post yesterday.
It cited discrepancies between data on the original loading capacity of the roof and that stated by the contractor and authorised person before the removable green roof tray system was laid atop the sports hall’s steel space frame roof at the university’s Kowloon Tong campus in December.
The wrong use of data was only spotted after the accident on May 20, largely due to the heavy reliance on the project’s sole contractor without seeking a third party’s advice, the report said. It cited “limitations” in the investigation due to the contractor and authorised person’s refusal to cooperate.
“The university should seek professional advice to take legal proceedings against those who are responsible or appear to be responsible,” committee chairman Professor Paul Lam Kwan-sing said.
The university is expected to sue Kenneth Chan Jor-kin, the professional who certified the project, and contractor Sinoway Construction Engineering. But a registered structural engineer and the university vice-president in charge of looking after the roof greening projects will escape punishment.
University president Professor Kuo Way expressed “regret” over the collapse, calling it a valuable lesson for CityU and the rest of Hong Kong. But Kuo said greening roofs was a global trend and one that even CityU should continue. “We are afraid, not of making mistakes, but of not taking action.”
While loading was identified as the crux of the problem, rain and the efficiency of drainage could also have been factors when the roof caved in.
Documents dating back to 1989 specify a maximum live load of 0.75 kilopascal (kPa) and dead load of 4.75kPa for the space frame roof. But an authorised person certification issued last October cited a different set of figures – a 1.5kPa live load and 10.25kPa dead load, which was mentioned in earlier design calculations that had been superseded.
Dead loads refer to permanent, built-in fixtures such as drainage systems, while live loads are additional forces such as people walking on a roof.
The weight of green roofing at the sports centre was also reported to be 0.66kPa despite soil samples taken from a nearby roof indicating a weight more than double that figure.
The committee stressed there were “enough reasons” to conclude surveyor Chan was the appointed authorised person for the roof, although he has denied responsibility, and he refused to comment yesterday.
The Education Bureau and Buildings Department said they would study the report carefully, with the latter pledging to take into account the findings of its own investigation. As the accident site remained inaccessible, more time was needed, it said.