Floored by poor practices

By ANNE GIBSON

The earthquake scare about precast concrete floors is hitting at the wrong target, says an industry chief.

Mark Binns, chief executive of the concrete and construction groups of the $1.4 billion Fletcher Building firm, last week wrote to Commerce Minister Lianne Dalziel, responding to her comments on the release of two reports on the structural design and construction of commercial buildings, from the Institution of Professional Engineers and the Building Industry Association.

Both investigated concerns raised by structural engineer John Scarry earlier this year about the performance of high-rise buildings in a major earthquake.

"Fletcher Building Limited group companies are leading participants in both the concrete and construction industries. It is therefore a significant concern that the media reporting on this issue seems to be biased to the sensational and lacks balance." Binns wrote.

He said precast concrete floors were being blamed when poor standards were the problem.

"The factors that have led to some poor practices in the construction and professional engineering industries are numerous, complex and interrelated. Very few emanate from any building product or system that is innately defective.

"Most would appear to result from over-zealous cost-cutting in design, a dearth of skilled labour in the industry and the lack of rigour in the regulatory regime to counter the decline in overall standards that has occurred over the last 10 years.

"We have industry standards for the structural integrity of concrete structures that are regarded as leading edge. They are most certainly not Third World as has been the inference," he said, responding to comments from his boss, Fletcher Building chief executive Ralph Waters, who said precast concrete floors were used only here and in South America.

"Canterbury University research that indicated potential problems with precast hollow-core flooring in certain severe seismic conditions was partially sponsored by Stresscrete, a Fletcher Building company.

"These tests were a world first for tests of this scale and I do not believe that other structural building materials, such as steel, have been subjected to the same test conditions.

"The results ... have been taken very seriously and a technical advisory group from industry, the engineering profession and the universities was immediately constituted to review and interpret the findings.

"The level of distortion applied to flooring in the Canterbury tests was higher than design requirements here for structures and simulated a 500-year return event in Wellington or in excess of a 2000-year event in Auckland.

"Any structural system will fail under the most severe seismic conditions. As with any discipline, engineering knowledge will improve and there will always be areas that require further research or refinement.

"Hollow-core flooring is a product that has been used extensively throughout Western Europe, in Britain, France, Spain and Italy. It has been used in Japan and the United States for the last 30 years.

"It complies with all building codes in these countries. Some of Scarry's initial comments on failures of hollow-core flooring at Northbridge, California, in the earthquake of 1994 are just factually incorrect."

Scarry defended his report, saying he was not against precast concrete floors nor in-situ flooring. But he said testing at Canterbury by Professor John Mander and his team provided worrying results.

"The testing on reinforced concrete frames supporting hollow-core flooring showed a completely unacceptable brittle failure and collapse of the floor units," Scarry said.

"Over the last 14 years at least, various tests have raised more and more concerns about precast floor units and the effect all floors can have on building response in an earthquake.

"The results of these few tests and the resulting limited recommendations have generally been ignored in practice."

Scarry objected to comments from Institution of Professional Engineers board member Dr Kelvin Walls and Auckland disputes arbitrator Geoff Bayley, who defended precast concrete flooring in the New Zealand Herald commercial property section on June 18.

"Dr Walls is incorrect when he says that prefabricating floors off-site results in better high-rise buildings and that one should blame work practices, not process," Scarry said.

He said Bayley was wrong to comment on matters of structural performance and to say that precast flooring predominates due to financial and time factors. Precast concrete flooring was often a slower method than in-situ flooring, he said.

"In California - using modern formwork systems and reinforcing every bit as dense as that used in Wellington - concrete contractors can construct in-situ multi-storey buildings at the rate of one floor every four days. Using precast, Auckland contractors struggle to achieve one floor every seven days."

Scarry called for a combination of factors to solve safety issues and improve standards.

"The keys to good precast design and construction are widely accepted good practices, skill and time to achieve excellent detailing, proper emulation of cast in-situ joints, a very large pool of very skilled draftsmen, very good site practices and a widespread appreciation of where precast concrete is not suitable.

"All these things have been lacking in the construction industry here for many years."

Full text: the Scarry report