Floor designer

Stairs, floors, columns and beams were found to be weakest in the Heretaunga Block of Hutt Hospital

The new organization replacing the DHBs is urging authorities to think carefully before closing the main block of Hutt Hospital.


Photo: RNZ / Dom Thomas

The Hutt District Health Board (DHB) has notice published he received on the seismic building which houses the care, maternity and vital radiology departments.

Reviews confirm that stairs, floors, columns and beams are the weakest points.

The four elements make up just 15% of the New Building Standard (NBS), according to documents released today.

DHB has published the engineering advice he has overcome his earthquake-prone medical block in recent weeks.

If a building has a low NBS percentage, it does not mean that it will not be damaged, but it does mean that people are more likely to be injured in a large earthquake.

Engineers discovered that the frameworks of the seven-story block did not have enough strength to withstand a 1,000-year-long earthquake – called a “design earthquake”.

Various reviews indicate that the columns and beams on the third and fourth floors and the roof are the most susceptible to failure.

However, Health New Zealand said engineers “do not necessarily expect a life safety hazard to occur in more frequent moderate earthquakes”.

Health NZ, which takes over from DHB next month, said last month that the block was not considered unsafe or at imminent risk of collapse, and that DHB should not make a hasty decision on whether to close it – that would require a service impact assessment, he says.

The risk to occupants over the next two years was considered low.

“From a technical risk perspective, there is no reason why this building should not continue to be used in the short term as options to provide medical services in alternative locations are developed,” the official said. engineer from Health New Zealand. .

Maternity and vital radiology services housed in the block mean it should be considered a Level of Significance 4 (IL4) building, which increases earthquake loading by 40%, said review engineers Silverster Clark .

At IL4, it wouldn’t be worth fixing, Aurecon lead engineers said last month, when detailing an elaborate series of hardening options for the DHB.

This “would be excessive in terms of cost” at the IL4 level, he said.

Repairing it would be very difficult and would take two to three years even if it were completely drained, while a staged remediation would take much longer, Aurecon said.

The Ministry of Health has been seeking for months to upgrade any radiology building to IL4 status.

The DHB knew the department was doing this, when it presented a 10-year-old seismic assessment last year to persuade Hutt City Council that the block was not earthquake-prone (less than 34% of NBS). The board accepted the outdated DSA.

This 2011 DSA found similar weaknesses and identified undesirable ways the tower might “collapse”, but rated the building at 43% NBS.

The various ratings and reviews now published note that the stairs could collapse and heavy concrete panels outside would fall on people during a major earthquake.

“The failure of these objects potentially poses a risk to life safety due to the falling objects themselves,” Silvester Clark said.

The company has yet to complete a full review of Aurecon’s Detailed Seismic Assessment (DSA).

In addition to the superstructure’s weak spots, the foundations are also poor, rated at only 20% NBS on liquefaction-prone ground.

“Under liquefaction, the lateral resistance of the piles was negatively affected, which contributes to the low NBS percentage of the foundation,” Aurecon told DHB last month.

“This failure is likely to result in a softening of the building response, which may reduce the earthquake impact of the building superstructure but would also result in permanent lateral and vertical displacement of the building.”

The floor has been designed in such a way that it is inherently strong, however, engineers say the floors at roof, first floor and ground floor level would shift in a way that could compromise parts verticals of the structure.

Elsewhere, they state, “in addition, the Heretaunga block has a flat slab floor slab system which has performed poorly in past earthquakes”.

The target NBS of 100% equates to a one in a million chance of death in a design earthquake; the 15% Heretaunga has a 1 in 40,000 chance, with a 25 times higher risk.

On June 2, the health board agreed to ask Health NZ and the Department of Health to commit to rebuilding on the hospital site “a fit-for-purpose building that meets the healthcare needs of current and future health of the Hutt Valley community”.

As for getting out of the tower, the DHB wants that to happen quickly.

“The option to stay in the Heretaunga building longer than necessary to practically leave is neither appropriate nor viable,” its minutes read.

It must be emptied “as far as possible and as soon as reasonably possible”.

An implementation plan is expected by June 22, along with planning for engineers to identify and implement temporary measures to minimize risk to people’s lives in the interim.