Professor of Civil Engineering at Canterbury University, and member of the NZ Wood management, Andy Buchanan speaks on material developments which can and should be saving more lives.

A shocking image in the aftermath of the recent Haitian earthquake is the Haitian presidential palace, collapsed and abandoned.

Andy Buchanan of Canterbury University says that if the palace in Haiti had been built with a modern structural framework of wood, chances are it would not have collapsed so badly.

While the palace is understood to have been built of reinforced concrete, Prof Buchanan says the worst buildings in earthquakes are built with un-reinforced masonry. Many of those in Port-au-Prince are believed to fall into this category.  Buchanan reflects on New Zealand's position in all this:

Andy Buchanan: New Zealand engineers learned the lesson in the 1855 Wellington earthquake. The old Government Buildings, built in 1876, have proved that wooden buildings can last the distance.

New engineering techniques now allow multi-storey buildings to be constructed of wood and can mean buildings surviving major earthquakes with very little damage.

Product Spec: And comparatively with concrete buildings – how do they perform?

AB: Badly designed concrete buildings behave like un-reinforced masonry buildings. While modern concrete buildings can be excellent, one disadvantage is their heavy weight.

You need both strength and flexibility for a building to perform well in an earthquake, but weight is one of the most important factors. The mass of the building can amplify the shaking.

PS: And what about steel?

AB: Steel has the advantage of flexibility. Being a very ‘ductile’ material, it can perform very well in a well designed building and in fact, both wooden and concrete buildings rely on steel’s ductility in either their reinforcing or the connections between members.

But because of its weight-to-strength advantage combined with its natural flexibility, timber buildings can perform just as well as concrete or steel buildings.

PS: Isn’t there a greater fire risk with timber buildings?

AB: Well designed heavy timber buildings can perform very well.

Fire performance is only a disadvantage for wood if the buildings are poorly constructed with inadequate plaster-board protection of light timber framing and a large number of buildings very close to each other. Modern, well designed multi-storey timber buildings have more than enough fire resistance.

Large wooden beams do not burn easily – they tend to char on the surface only and remain structurally intact - just think of all the tall tree trunks left standing after a devastating forest fire - and can actually perform better than unprotected steel which can lose its strength very quickly.

Mostly what burns in a building fire is not the wood or the wood structure, it’s the solid petrol in all the foam and plastic in the finishings. This is a problem regardless of whether the building’s made from wood, steel or concrete.


Fire Performance Testing.

Seismic Shake Testing.

Strength testing.

PS: As we discussed briefly in our last chat, you’re working on new techniques for using wood to build multi-storey buildings, could you elaborate?

AB: At Canterbury we’re developing multi-storey timber post-tensioned buildings which incorporate tensioned steel cables together with laminated wood beams, a technique that is also used in some concrete building designs. The steel cables provide extra strength, elasticity and earthquake resistance.

PS: Have multi-storey wooden buildings been put to the test in terms of earthquake performance?

In the last few years six and seven storey wooden buildings have been tested on the world’s largest shaking table in Japan at simulations of magnitude 7.5 earthquakes and have shown almost no damage.

For the last 30 years the guiding principle for earthquake engineering in New Zealand was ‘capacity design’ where the objective was to allow for small ‘controlled’ failures but to avoid collapse of the building.

The aim was that in a small earthquake there would be no damage, in a medium-sized earthquake the damage would be reparable with the structural integrity of the building retained, and for the largest earthquakes the building may suffer non-reparable damage, but there would be no collapse.

Now, and only now, are people thinking about being able to resist a large earthquake with no structural damage.

This is the way things are moving in the earthquake engineering world. Steel and concrete construction engineering is working towards this, and our new wood construction techniques are advancing right along with them.


Andy Buchanan is Professor of Civil Engineering at Canterbury University and is a member of the management team for NZ Wood.