An expert panel probing the collapse of buildings in Christchurch wants councils to act more quickly to identify older buildings that do not meet current design guidelines and could pose a danger.
It is worried that many older buildings not classed as earthquake-prone would not be safe in a major earthquake and that not enough attention is being paid to improving their seismic performance.
The five-storey Pyne Gould Corporation (PGC) building which collapsed in the February 22 quake, killing 18, was not considered to be an earthquake-prone building even though it did not comply with current building design standards. It met design guidelines at the time it was built in 1963, but it was not resilient enough to withstand the intensity of the ground shaking recorded during the magnitude 6.3 quake.
The ground-shaking intensities recorded in Christchurch's CBD during the quake were well in excess of those used as a basis for building design in the 1960s, the 1980s, and currently. The PGC building lacked resilience and the ability to move and respond to the intense shaking without losing strength, the expert panel concluded in the first of two reports it is preparing for the Department of Building and Housing.
The panel, chaired by construction law expert Sherwyn Williams and comprising top structural engineers and geotechnical experts from both here and overseas, has yet to reach a conclusion on why the Canterbury Television building collapsed. It says the collapse of the CTV building is more complex and it needs to do more analysis before releasing findings on why that building collapsed, killing more than 100 people.
The panel has concluded its investigations into why major building components of the Hotel Grand Chancellor and the Forsyth Barr building, both of which were constructed in the 1980s, failed. Two flights of stairs collapsed in the Forsyth Barr building during the quake; the main stairs collapsed from level 15 down and the other flight collapsed from level 13. The panel concluded there was an insufficient "seismic gap" around the stairs, which meant they could not slide horizontally and fell off their supports.
The Ministry of Building and Housing has issued an urgent advisory warning building owners to check that all main exit stairs have sufficient allowances for movement. It has also written to all councils asking them to alert owners of multi-storey buildings to the importance of having their stairs checked by a chartered professional engineer.
At the Hotel Grand Chancellor a critical concrete shear wall, which supported about one-eighth of the building's mass, failed. The south-east corner of the building also dropped about 800mm, causing the building to develop a horizontal lean that in turn led to the collapse of the stairs.
The panel has recommended that owners of buildings built before 1976 should be alerted to the fact that lightly reinforced shear walls with little or no confining steel can be vulnerable in an earthquake and that they should obtain advice from an engineer.
Its report has been given to the Royal Commission of Inquiry conducting an investigation into the building collapses in Christchurch.