New analysis of Christchurch building design

New analysis of Christchurch building design

How Christchurch can be rebuilt so as to have greater resistance to potential future shocks has been the question on many a mind, and now an information paper just released by the Royal Society of New Zealand (RSNZ) hopes to provide some direction for the city’s design future. But it’s not all about the future. The paper also analyses earthquake damage to buildings in Christchurch from the 4 September earthquake, and its associated aftershocks. 

It looks to be well qualified too, culminating in a raft of science and engineering expertise from the likes of the Institution of Professional Engineers New Zealand, the Structural Engineering Society New Zealand, the New Zealand Geotechnical Society, the New Zealand Society for Earthquake Engineering, and of course, the RSNZ. 

The above organisations are hoping the paper will provide better public understanding about designing buildings to resist earthquakes, and the new lessons to be learnt following the Canterbury earthquakes 

The RSNZ says the paper provides answers to important questions like: 

* What is an earthquake prone building?

* Why did buildings collapse in these earthquakes?

* Given that a building has been through one earthquake, how do we know how much of its “earthquake life” has been used up? 

“We hope that by bringing together information on these issues, some of the questions and concerns which people have will be answered,” says RSNZ vice president Professor Keith Hunter. 

You can download the paper in full HERE, but in the meantime, here’s an expert on the lessons learned form the earthquake and what low cost methods can be applied to improve earthquake safety. 

What are some of the new lessons from the earthquake sequence?
  • 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. 
  • What are some 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 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.
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