Expert at quake inquiry questions use of shear walls

5:54 pm on 18 January 2012

The use of shear or exterior walls to hold up buildings has been called into question at an inquiry into the Canterbury earthquakes.

A Royal Commission into the Canterbury earthquakes has resumed and has focused on how the Hotel Grand Chancellor withstood the 6.3 quake on 22 February last year.

It is looking at why the 28-storey building slumped by almost 1 metre when one of its major load bearing walls failed, and was thought to be at risk of total collapse following the quake.

The failure of a shear wall (a supporting wall) has been pinpointed as the reason why Christchurch's tallest building almost collapsed.

Structural engineer Adam Thornton continued to give evidence on Wednesday, saying the February quake was a wake-up call for engineers regarding the use of shear walls.

Mr Thornton says in the past, it was thought shear wall buildings did not fall over in earthquakes and this had resulted in them being put under higher loads and stresses than they are suited for.

Asked if the 1980s hotel would have held up if it was built to comply with the current building code, Mr Thornton said the code had actually become more lax since the 1980s when it comes to shear walls.

More work needs to be done on how effective the walls actually are at holding up large structures, he said

Hotel 'stood high chance of failing'

Earlier, a US-based engineer has added his voice to the view that the Grand Chancellor Hotel stood a high chance of failing in an earthquake such as the one which hit the city in February.

Structural engineer William Holmes, based in San Francisco, told the Royal Commission he was surprised at the slenderness of the shear wall which failed in the earthquake.

Mr Holmes has been hired by the commission to peer review the report into the failure of the building carried out for the Department of Building and Housing.

He says the fact that the shear wall did not include a greater level of reinforcing is most likely the result of the architect not wanting a large wall taking up most of the hotel's lobby.

Mr Holmes says engineers are hired by architects and have to try to work with what they are given.

Building strength 'should exceed predicted risk'

Another expert in structural engineering told the Royal Commission that buildings should be designed to be as strong as possible, not just to meet earthquake-risks outlined in mathematical modelling.

Stephano Pampanin of the University of Canterbury told the commission that problems occur when buildings are designed to just meet an expected risk.

He said the Christchurch quake showed that the impact can vary hugely depending on how close the epicentre is to the building.

"If we design more robust buildings then they are going to be robust even in the case of not known or stronger than design type of earthquakes."