3 Oct 2021

Confusion and frustration over dated but legal earthquake rules

8:51 am on 3 October 2021

New research shows there are tangled earthquake rules that could lead to owners strengthening the wrong parts of buildings, or having to pay twice to find out if their floors are safe.

BNZ Harbour Quays building.

BNZ Harbour Quays building. Photo: RNZ / Phil Pennington

Engineers are urging officials to untangle what they call "this confusion", but there is no sign when that might happen.

The research for the Ministry of Business, Innovation and Employment (MBIE) compared the two sets of rules for engineers doing seismic assessments of commercial buildings.

Not surprisingly, it's found the newer rules are superior - but unfortunately only the older rules have legal standing.

New Zealand has thousands of multistorey buildings with particularly weak types of precast concrete or hollowcore floors, which it has been known for 30 years are especially risky, and which sustained a lot of damage in the 2016 Kaikōura quake - as exemplified at the BNZ Harbour Quays in Wellington, where floors cracked and sagged.

Cracks in the supports for floors in the BNZ Harbour Quays building in Wellington after the 2016 Kaikoura earthquake.

Cracks in the supports for floors in the BNZ Harbour Quays building in Wellington after the 2016 Kaikoura earthquake. Photo: WSP Opus report.

Researchers have found the rule manual introduced hurriedly in 2017 - the so-called Red Book - produces similar overall quake ratings (or New Buildings Standards - NBS) as the newer rules created in 2018 in response to Kaikōura.

But it also shows the older rules are not as good at spotting a building's weakest parts, especially not for concrete buildings or for floors, which typically are the weakest part.

"This means that the [two approaches] identified different vulnerabilities in buildings, implying that retrofits based on the Red Book may not address a building's greatest vulnerabilities," said the new report.

This made a complex situation worse, it said.

Businesses "want to know that retrofits address the weaknesses in their building that pose risk to people's lives and safety" but the two sets of guidelines did not promote confidence.

Yet only the Red Book contains the rules that are legally mandated for use in determining if a building is quake-prone.

The newer rules (called the Yellow Chapter, or Yellow Book) carry no such weight, even though engineers trust them more.

"There is a confusion and frustration for engineers," said one of the researchers, Dr Nicholas Brooke, echoing the report's repeated line that the industry wants the superior, newer Yellow Chapter to hold sway.

The confusion could lead to a building owner being forced to get a quake-prone assessment done under the Red Book, then having to get a second assessment done under the Yellow Chapter, Brooke told RNZ.

Dr Nicholas Brooke.

Dr Nicholas Brooke. Photo: Supplied

"It will, in some circumstances, result in additional and arguably unnecessary cost for building owners."

MBIE's Manager Building Performance and Engineering Jenni Tipler said they must consider the findings from the research before deciding whether to incorporate the Yellow Chapter into legislation.

It had to always balance evolving engineering knowledge against the "need to provide certainty for the sector".

As for retrofits, this was separate from assessing a building's NBS, she said.

"It is usual for additional work to be identified and incorporated as the remediation plan is developed.

"Building owners should have certainty that, having complied with the mandatory national requirement, the compliance level would not be changed over the short term."

It said in an earlier statement that first it wants to figure out the impacts on "the building system" if it were to alter what is mandated.

The ministry has yet to assess these impacts, though the Yellow Chapter was brought out three years ago.

The new research for MBIE says there are already impacts from not making the change, such as building owners being reluctant to get a seismic assessment done at all.

"They want confidence that retrofit work is be aligned with any imminent regulatory environment.

"They expect regulation to be based on the latest knowledge," it said.

Instead, "businesses and government agencies vacating buildings has contributed to this confusion", in a doubling-down over their health and safety duties.

Brooke said in practice, engineers are not using the older Red Book unless it is legally demanded in situations where the building owner has to respond formally to a council. This was not happening much with respect to 1980s-90s buildings constructed when the weak precast floors were a ubiquitious design.

"The industry is making it work fairly well, I think, in the sense that the Yellow Book is used for almost everything," he said.

Very few Red Book building assessments exist.

New Zealand is unusual worldwide for the high proportion of commercial and apartment buildings with the weak type of floors - more than 60 percent of commercial floor area in Wellington falls in this category.

Research on how to fix them only began in earnest after the Kaikōura quake.

This late start cast structural engineers "in a poor light", said Brooke and other leading researchers in 2019.

By mid-2021, it had been established the floors could be "highly vulnerable" and fail in many ways incuding "web splitting", and the floor slab falling off its seating, as happened at Statistics House in Wellington in the Kaikōura quake.

Research by the country's leading project into retrofitting such floors, ReCast Floors, at about the same time revealed key findings:

  • Buildings in Wellington may have undetected web cracks, which decrease what load they can bear
  • Figuring out the extent of that decrease is difficult
  • Some floor connections (called Beta units) can be "highly susceptible to damage"
A strongback system - a retrofit  now being recommended in NZ -  is tested by ReCast Floors researchers.

A strongback system - a retrofit now being recommended in NZ - is tested by ReCast Floors researchers. Photo: ReCast Floors Research

As a consequence, the industry is being advised not to put up any more buildings with hollowcore floors - and an industry source told RNZ that advice is being followed.

On the upside, the ReCast project thinks it has found a pretty good retrofit fix, called the 'strongback system' which it is testing further.

The project's final results are due early next year.

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