Quake building collapses explained

The collapse of the Pyne Gould Corporation building has been blamed on strong shaking and "exceptionally high" vertical movement. Photo / Geoff Sloan

Lax building standards contributed to the collapse of a 40-year-old building in which 18 people died during the February 22 Christchurch earthquake, a new report says.

The Department of Building and Housing (DBH) this afternoon released its technical investigation into the collapses of the Pyne Gould Corporation (PGC), Forsyth Barr and Hotel Grand Chancellor buildings.

However, the report does not delve into the reasons for the devastating collapse of the Canterbury Television (CTV) building, where more than 100 people died.

It said the PGC building collapse, where 18 people were killed, happened because shaking was several times more intense than the structure could withstand.

Though the building had met design requirements during its construction in 1963, regulations had been tightened since then, the report said.

An extensive 1997 study had confirmed the building was not up to standards for earthquake resilience at that time, it said.

"In the case of the PGC building, where there was tragic loss of life, the shaking was much more intense than the building was designed for in 1963 and the building lacked resilience and the ability to move and respond without losing strength."

Experts found the partially collapsed Hotel Grand Chancellor was "generally well designed".

However, a vulnerability in one of its shear walls resulted in a major, but local, failure, the report said.

"Other shear wall failures of similar appearance have been observed in other buildings following the 22 February 2011 aftershock, and this suggests that a review of both code provisions and design practice is warranted."

The report found the collapse of a stairwell in the Forsyth Barr building was brought on because the stairs were not equipped for an event of the magnitude of the February 22 aftershock.

Intense shaking during the shock exceeded the capacity of the stairs to move on their supports, the report said.

It was possible the gaps at the lower building supports had been filled with material that restricted movement.

Building and Construction Minister Maurice Williamson welcomed the release of the report.

The technical investigation on what caused the collapse of the CTV building was far more complex and would be delayed until the end of the year or early 2012, he said.

"There are several possible reasons for the failure and the expert panel is adamant that additional analysis is necessary. The families of those injured or killed and the survivors deserve findings based on a thorough and robust investigation."