Christchurch earthquake, buildings and acceleration maps

By Grant Jacobs 29/06/2011 4

Just released by the Royal Society of New Zealand today (June 29th, 2011) is an information paper The Canterbury Earthquakes: Answers to critical questions about buildings (PDF file, 718kb).

It’s well worth reading – not just for those in Christchurch, but anyone in earthquake-prone areas in New Zealand or elsewhere, or the merely curious.

This work presents questions and answers in a joint effort by ’the Royal Society of New Zealand, the Institution of Professional Engineers New Zealand, the Structural Engineering Society New Zealand, the New Zealand Geotechnical Society and the New Zealand Society for Earthquake Engineering, who have co-ordinated science and engineering expertise from across New Zealand.’

(Update: Take-home points at end of this post.)

In addition to talking about buildings they have presented the peak horizontal and vertical ground acceleration recordings for the February 22nd and June 13th events onto maps (shown below).

February 22nd 2001 Peak Ground Acceleration

February 22nd 2001 Peak Ground Acceleration
June 13th 2001 Peak Ground Acceleration

June 13th 2001 Peak Ground Acceleration

I hope our building expert and colleague, Ken Collins, can fill in with more details!

Updated with the take-home points from the end of their article for those (like me!) with little time. Those with time should dig in for the details.

What are some of the new lessons from the earthquake sequence? There is more to learn but so far:

  • Modern buildings on good foundations, constructed according to the building code in force now, protected lives even though shaken to a greater extent than the code design level.
  • Better designed foundations than those used at present are needed to counteract the effect of liquefaction, especially for houses. Engineers are already working on this.
  • Non-symmetrical buildings can behave poorly if careful design is not conducted.
  • Potential rock falls on hillside areas overlooking towns and suburbs have to be recognised, and appropriately considered.

What are some low cost methods of improving earthquake safety? There are a number of relatively low cost methods of improving earthquake safety.

For homes:

  • Secure heavy items, such as header tanks, and tie back water cylinders.
  • Brace, strengthen or remove brick or other unreinforced masonry chimneys. Strengthening may be achieved with a galvanised steel tube grouted into the chimney flue. Where the chimney is to be removed, demolish completely if located externally, and down to ceiling level if internal. Replace chimneys with code-compliant steel flue. Where architectural form requires a chimney above the roof plane, install a fibreglass replica. Ensure all new chimneys comply with the Building Code.
  • When building, use ’earthquake friendly’ materials like piled or waffle-slab foundations, timber (or light steel frame) walls and lightweight roofs.
  • Remove heavy roofs like concrete tiles and replace them with lightweight materials such as steel.
  • For remedial works on houses, see the Department of Building and Housing advice. [edited to include link directly]

For larger buildings:

  • Consider enhanced seismic performance and design requirements at the time of design
  • Make structures as symmetric as possible, not necessarily to the detriment of architectural form
  • Remove or strengthen poorly attached heavy architectural ornaments and parapets on old buildings.
  • Increase the strength of brittle building components, for example by fitting steel bracing frames in low rise concrete frame buildings.
  • Strengthen the buildings with strong and ductile systems that have increased stiffness to limit the displacements.

(My apologies for the short entries of late: my writing elsewhere is taking time away from writing contributions for this blog; hopefully this will come right in a few days time.)

Other articles on Code for life:

The Christchurch / Lyttelton earthquake aftershocks news thread

Liquefaction in a barrow

Is your computing desk well set up?

Literate and test-driven programming (in bioinformatics)

“Knowledge is merely opinion.” Storm – in cartoon and words

Preserving endangered species – of gut microbes

4 Responses to “Christchurch earthquake, buildings and acceleration maps”

  • Thanks Brigid.

    I’ve updated the post to include the take-home points from the end of their article for those in a hurry. I encourage people to dig in to the full document though – a lot of effort has gone in to making the paper useful.

  • Should have added: ironically New Zealand research into building design to resist earthquakes in the paper is described as “Groundbreaking”. Um?

  • Very interesting thanks. Figure captions in the pdf are correct, but the ones in this post should have the date as 2011 rather than 2001.

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