Engineers are calling for urgent tests on a type of concrete floor prone to cracking in big earthquakes, that are common in multi-storey buildings.
Photo: RNZ / Rebekah Parsons-King
In a report to Wellington City Council today, engineers from the Kestrel Group identified damage to 72 buildings targeted for extra inspections after the Kaikōura earthquake.
The report does not name the buildings, as the individual engineering reports on them are confidential, but said engineers must be more careful in giving buildings with the hollowcore floors a seismic rating.
It said working out just how strong the hollowcore floors that cracked last November were now should be a priority, and said it was also urgent to find a standard way to repair them
Damage to a beam identified in the report. Photo: Kestrel Group
Eight buildings were badly damaged in the quake, with Statistics House the worst.
"Critical" structural damage was mostly to floors, including extensive cracking.
Of the 64 other targeted buildings, most of the damage was in ductile-frame (flexible) buildings with hollowcore flooring built in the 1980s. The report also found 40 percent of those 64 had no damage.
It said the quick, once-over checks of buildings straight after the quake had not identified all the structural damage. This, it said, showed up the value of going back for targeted inspections.
The report made nine recommendations, two of which were about hollowcore floors.
There are 152 buildings in Wellington with this type of floor.
The report said there were also other buildings in the city with structural damage, but the council would not give further information on them.
"We have limited visibility of buildings that were not included in the [extra inspections], and no regulatory means of compelling information to be provided, and cannot provide a definitive answer," the council said.
"We engaged with all engineers in Wellington (and many from outside the City) during this process ... and we have a high degree of confidence that the engineering sector is aware of the issues. Engineers are obliged to act if safety is compromised."
Other recommendations included that a panel be set up ready to quickly advise on emergency work on buildings after a big earthquake.
Another was to fit more buildings with quake-measuring instruments to show if an earthquake had hit a building beyond its designed capacity to withstand it.
The council was already trialling that in 10 of its buildings, and hoped to get them in 400 private buildings, but that could cost $50,000 to set up and tens of thousands of dollars a year to monitor.
The council said it was not unreasonable for tenants to be able to see all information about their building, and increasingly building owners were sharing engineer's reports and seismic New Building Standard (NBS) ratings with them.
The government has given Quakecore $187,000 for four months' research, starting in June.
Director Ken Elwood said the earthquake had shown that there were some damage patterns that had not been seen before in Wellington.
"We need to understand exactly what that means in terms of the capacity of those floors in future earthquakes."