Preliminary Structural Essessment of a log home after Christchurch earthquake
– by Batchelar & McDougall Consulting, Structural & Civil Engineers, 2011
Wood ideal material for rebuild
Wigram MP and Progressive Party leader JIM ANDERTON explains why he favours rebuilding Christchurch in wood.
‘Ridiculous” and “stupid” are how Richard Field, the Canterbury president of the Master Builders’ Federation, described my recent call to use wood as a primary construction material in the rebuilding of post- earthquake Christchurch. Setting aside the obvious question of why a building industry leader would dismiss wood in this way, the comments from Mr Field ignore mounting scientific and engineering evidence which shows that wood has the characteristics and qualities needed for a safe, modern city. As well as being safe, there are a host of other reasons why wood should form the mainstay of Christchurch’s building recovery – it is ecologically sound and sustainable, it is less expensive than many alternatives and it’s an attractive, iconic New Zealand product. There is another aspect too, and that is in the psychological recovery of the thousands of people who work in the inner city, many of whom now live in fear of working again in high-rise buildings. Those people need to feel secure, and wooden buildings, even up to six storeys high, can afford them that security.
On February 22, 2011, it wasn’t just old brick and stone buildings which crumbled under the force of the magnitude-6.3 earthquake; the most notable casualties, both in terms of building collapse and loss of life, included the CTV and PGC buildings, the stairwells of the towering Forsyth Barr building and the Hotel Grand Chancellor. All were modern buildings, their construction primarily of concrete and steel. That alone is as good a reason as any for serious consideration to be given to alternative construction materials.
Since 2007, research carried out under the guidance of Professor Andy Buchanan at the University of Canterbury has looked at the potential for commercial buildings to be constructed of wood as opposed to concrete and steel. That research was motivated in part by the Government’s wish to pursue policies towards greater sustainability; its rationale including that modern engineered wood products, along with advances in structural timber engineering and innovative design, positioned timber as a viable alternative to concrete and steel for multi-storey buildings. There are a number of other reasons to look at wood for major construction work. It is a renewable, low-energy resource. There is a plentiful, sustainably grown supply in New Zealand. Modern timber construction produces little waste and the manufacture of building materials from wood is now generally non-polluting. Additionally, the increased use of wood would provide national benefits in the long term, including reduced fossil fuel consumption and CO2 emissions, an increase in the pool of retained carbon in wood and wood products, and the potential for the replacement of fossil fuel by burning wood waste materials. There are other benefits, including that the energy consumption requirements of wooden buildings are the same or lower than those made of concrete and steel, and construction costs can be cheaper overall. Lastly, at the end of their lives, buildings constructed of wood will have more reusable material than their concrete and steel counterparts and they are more easily dismantled for reassembly elsewhere.
Safety will, of course, be paramount in the rebuilding of Christchurch. It is likely that many will be wary of high-rise buildings, meaning it is hard to imagine that new buildings will be more than a few storeys high. Back in 2007, when most people never anticipated that Christchurch was in any way prone to earthquakes, Professor Buchanan and his team concluded that the lightweight nature of predominantly timber buildings required a lower earthquake loading than reinforced concrete ones, wood being one- quarter the weight of concrete for the same-sized components.
Clearly, wooden buildings have more “give” or flexibility, added to which the researchers concluded that timber construction was ideally suited to multi-storey building because of its high strength-to-weight ratio.
Another benefit noted by Professor Buchanan and his colleagues was that the new construction engineering methods, particularly using laminated wood, had changed plain old radiata pine from an export commodity into a high quality engineering material.
There seems little sense in exporting raw logs when they could be successfully turned into high quality construction products right here and save on the need to import other construction materials. In other words, we can create jobs rather than export them.
Another important element when it comes to safety is fire resistance. Strange as it may seem, large wood beams have excellent fire resistance because the slow rate of surface charring protects the wood inside the beams and columns. Fire safety is further increased by sprinkler systems, giving people time to evacuate buildings during an emergency.
Compare that with the collapse of the Twin Towers in New York during the 9/11 event, where the steel frame lost strength as a result of fire. That sort of collapse would be unlikely in a wooden building.
The New Zealand Building Code was amended in 1992 to allow timber buildings of unlimited height, subject to some performance requirements. Before that, three storeys was the maximum height for wooden buildings. Fire safety was one of the influential factors in the change.
It has been a number of years since timber was used extensively in commercial construction in New Zealand, but it is not difficult to find some exceptional examples, both here and overseas, of successful, large wooden buildings.
The historic Government Buildings in Wellington, now occupied by Victoria University, is a fine example of a large, multi- storey building which has stood the test of time. In parts of Europe six- storey wooden buildings are common, while in North America the norm is four storeys. In Norway, a 20-storey high-rise tower is being built using laminated wood for its beams and columns and wood panelling throughout.
There is no reason why Christchurch cannot become a world leader in innovative, medium-rise wooden commercial buildings. The timber construction industry says that the country has sufficient wood resources to supply whatever is needed, and we have among us the designers, architects, construction engineers and builders who could do the job.
It is a pity that Mr Field from the Master Builders’ Federation has dismissed the idea without considering the evidence, but it is good to know that the idea has the support of many others, including prominent architects, government ministers and even the Mayor of Christchurch. With that support we could rebuild our city in an attractive, safe and sustainable way. With wood. Why wouldn’t we?
– The Press