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Hotel Grand Chancellor - Source: Fairfax -
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Changes in the Hotel Grand Chancellor's design led to a "critical structural vulnerability" exposed in the February 22 earthquake, a royal commission has heard.
The Canterbury earthquakes royal commission resumed today, examining why the Cashel St hotel suffered such severe structural damage during the magnitude-6.3 tremor.
The southeast corner of the building dropped 80 centimetres during the quake after a shear wall failed and a number of staircases collapsed.
Demolition of the hotel is due to finish in April.
Structural engineer Adam Thornton, of Dunning Thornton Consultants, said the building's southeast corner was a clear weak point.
"In retrospect, if any wall was going to fail it is logical it is this wall. It is the one that is most vulnerable."
A late design change was required when the hotel was built in the 1980s after it was ruled Tattersalls Lane, east of the hotel, should be kept as a right of way.
Thornton's report to the Department of Building and Housing said this resulted in "a disproportionately large contributing area" that had to be supported by the failed wall.
"The developer attempted to get permission to put the structure within the right of way and the design was to proceed on that basis," Thornton told the hearing.
"Piling had already started on this side when the legal position was he could not found the building in the lane itself. Although he obviously had air rights over the top of the lane. The structure was then amended and redesigned to this format."
As a result, the force exerted by the quake was not evenly distributed throughout the building, he said.
"It was a critical vulnerability in this wall. It was too slender, the potential loads on it were underestimated," Thornton said.
Thornton will continue to give evidence this afternoon.
Canterbury University engineering associate professor Stefano Pampanin and San Fransisco-based structural engineer William Holmes will also present evidence before all three experts take part in a panel discussion later this afternoon.
Last month, the Commission heard how workers in the Pyne Gould Corporation building felt unsafe after the September quake, while engineers had deemed it fit for people to work in on four separate inspections.
Eighteen people died and dozens more were trapped when the PGC building collapsed in the February quake.
The 6.3 magnitude earthquake killed 182 people in Christchurch.
The Royal Commission, which began last May, will report on the causes of building failure as a result of the earthquakes as well as the legal and best-practice requirements for buildings in New Zealand Central Business Districts.
