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Sat 25 Feb 2012 08:57 PM

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Christchurch earthquake: Lessons learnt

A technical report has been released on the devastating New Zealand earthquake

Christchurch earthquake: Lessons learnt

It has been a year since a magnitude 6.3 earthquake struck Christchurch in New Zealand, wreaking havoc and destruction. Now a newly-released technical report on the collapse of the Canterbury Television (CTV) building has revealed that “the building was not built to code.” This finding is particularly tragic given that the 115 deaths in the collapse, including 65 foreign students, accounted for over 60% of the total number of deaths in the earthquake.

The damning report by the Department of Building and Housing found that the CTV building did not comply with the building code when it was built originally in 1986. Three factors played a critical role in the collapse: intense horizontal shaking of the ground; a lack of ductility in the columns, rendering them brittle; and an asymmetrical layout of the shear walls, which caused the building to ‘twist’ during the earthquake, thereby increasing the strain placed on the columns.

Other potential contributory factors were: low concrete strengths in some of the critical columns; exceptionally high vertical ground movement; possible interaction of the columns and concrete spandrel panels on the external façade, making the columns less flexible; separation of the floor slabs from the north core of the building; and the structural influence of the concrete masonry walls, rendering lower floors more rigid than the upper ones, which caused extra stress on the upper columns during the earthquake. While the investigation found it was not possible to derive at an exact sequence of the building’s collapse, the common denominator, as in most collapse scenarios, was the failure of one or more columns on the east face of the building. This was consistent with eye-witness accounts during the earthquake.

Earthquake-report.com also notes that ground motions during the Christchurch earthquake “were, in many cases, above the expected code ground motions; thus it would have been very difficult to build to such standards.”

No doubt the devastating Christchurch earthquake will contribute to this growing area of expertise, resulting in even safer structures in future that can withstand nature’s fury and at the same time protect their occupants.

The latest R&D in this area includes exciting work by University of Manchester mathematicians, who are fine-tuning the theory for a science fiction type ‘cloaking’ type device to protect buildings from earthquakes. Writing in the Proceedings of the Royal Society, Dr. William Parnell explained that, by cloaking components of structures with pressurised rubber, powerful waves such as those produced by an earthquake would not ‘see’ the building.

Instead, they would simply pass around the structure, and thus prevent serious damage or destruction. Such ‘invisibility’ could prove to be of great significance in safeguarding key structures such as nuclear power plants, electric pylons and government offices from destruction from natural or even terrorist attacks. It may sound esoteric, but hopefully such research will go a long to produce even safer buildings in the not-too-distant future.

Gerhard Hope is the Editor of Construction Week.

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