Low seismic ratings no threat – DHB

The South Canterbury District Health Board chief executive has defended the low seismic ratings of several hospital buildings, saying they don’t pose ‘‘a significant risk of failure in the shortterm’’.

Data, provided under the Official Information Act, showed only a fraction of the 29 facilities the DHB is responsible for have been seismically assessed.

Of those assessed, half are considered earthquake prone (EQP) or earthquake risk buildings (ERB).

A new building standard (NBS) is a rating given to a building to indicate its seismic standard, and ability to withstand an earthquake. Existing buildings are assessed relative to the structural earthquake standards of a new building.

The assessments for the DHB include the laundry and stores – which are assessed as reaching just 13% and 15% of NBS respectively, the main clinical services building – which is listed as reaching <34% of NBS, and the energy centre which reaches 50% NBS.

In a statement, chief executive Jason Power said the Timaru hospital campus has three main buildings – the gardens block, clinical services block and Kensington – as well as other buildings, “including maintenance and supply, and the laundry which we have not used for some years”.

Power said the gardens block was strengthened in 2016, and “is rated at 74% of the National Building Standards (NBS)”. The building that housed the boiler (which is no longer in use) will be upgraded for a new supply and maintenance building over the next 12 months, Power said

He said while the main clinical building “has an overall low seismic rating, due to specific elements, the building overall is not considered to present a significant risk of failure in the short-term,” a finding he said Ministry of Health engineers have supported.

Power said different parts of the building have different seismic ratings.

Of the buildings and facilities assessed that meet or surpass 67% NBS – the minimum level recommended by the New Zealand Society of Earthquake Engineers – the gardens block building has an assessment of 67%, garden block north reaches 74%, garden block south 96% and site-wide tunnels reached 100%.

It is not clear when the seismic assessments were conducted, or why so many of the buildings are listed as not having been seismically assessed.

‘‘The main clinical services building is made of cast in-situ concrete construction, with a number of bracing wall elements. These have a rating of 35% to 45% of the NBS at IL4.’’

The Building Code ranks buildings based on their level of importance to the public and the consequences of their failure, from level one (structures presenting a low degree of hazard to life or property, like walkways, outbuildings, fences and walls), to level five (structures whose failure pose a catastrophic risk).

Power said building standards have become more stringent since the Christchurch and Kaikōura earthquakes, which ‘‘means the overall rating [of the clinical services building] is 35% IL4.’’

The NBS rating reflects the lowest rating of the part of a building.

He said, in this case, that relates to lightweight rooftop extensions added in the 1980s, which are ‘‘the basis for the overall rating of the building to 34% of the NBS’’.

He said work to ‘‘tie’’ the extensions to the main building is underway, ‘‘with engineering designs to be completed’’.

‘‘Once the upgrades to the rooftop extension are completed, this will lift the NBS rating to greater than 35% IL4.’’

Power said the seismic assessment ratings are based on rare and severe earthquakes, and do not indicate a level of ‘‘earthquake shaking at which structural failure might occur,’’

‘‘It is important to note that these ratings are made against earthquake loadings corresponding to a 2500-year return period. A very rare earthquake that is almost twice as strong as that is used for office assessment of buildings.’’

‘‘. . . these ratings are made against earthquake loadings corresponding to a 2500-year return period.’’

Jason Power