In a city destroyed by earthquakes, and around the country as well, confidence in our built environment has taken a massive hit this week. After a decade of suffering stories about leaky buildings, and the recent quakes that have destroyed the centre of Christchurch city, what people need to have now is confidence in their architecture. That is something that has just not happened. Images of destroyed buildings, of twisted wreckage and destruction in the heritage architecture of the garden city, have saturated the press coverage of the 2011 Canterbury quake. Alongside that, we can notice people gathering in the open spaces, under the leafy trees of Hagley Park and other places. A city designed with open spaces is a resilient city – it is prepared and it will survive. The trees in the park are supple – they bend and sway in the force of the quakes – and then are back to normal again. In times like this, trees and open space are safe places to be.
Buildings are different. Buildings can kill you. Generally, architects and engineers try to design buildings that have stiffness built in, with bracing in the walls, floors and roofs to resist the onslaught of lateral forces like earthquake and winds. That works up to a certain limit and the limit is whatever we have designed it to. Currently, Christchurch and its surroundings are in an earthquake risk zone of low to medium risk. We can see now that this is woefully inadequate.
The materials we build our houses and our commercial buildings from have a huge effect on how well the buildings will survive a disaster. The coverage from the quakes has shown without doubt that brick and stone buildings constructed without adequate reinforcing are simply not adequate to the task of standing up to earthquakes. We live on the Pacific Rim of Fire – the world’s most well known zone of earthquakes and volcanoes. There will be severe earthquakes in New Zealand until the end of time. Our buildings need to be designed to meet this threat.
The resilience of our buildings is good compared to places like Haiti, where hundreds of thousands of people died in their massive earthquake, simply because they are poorly funded, have built from unreinforced masonry, from poorly reinforced concrete, and from unregulated building controls.
Reinforced concrete is a wonderful material for resisting seismic stress, and it is clearly evident that the vast majority of multistorey modern buildings in the Christchurch CBD, constructed to recent upgraded building controls, have resisted the earthquake with flying colours. The stresses unleashed in the earthquake on Tuesday subjected the buildings to forces far in excess of what we would expect them to be able to resist – and with only a few exceptions, have performed excellently. Concrete blocks have not performed nearly as well: in areas like Christchurch, concrete blockwork was often installed with only minimal reinforcement during the 1970s.
Concrete blockwork can work well, as long as reinforcement is installed through every block. Concrete blocks, like concrete itself, work on the basis of making everything stiff. Stiffness works well up until a point, but in an earthquake this size, a building needs to be not just stiff, but needs to be able to flex as well. Many of the ‘Christchurch Modern’ designs will have suffered structural collapse from the unreinforced concrete blockwork masonry, as shown here in this 1961 Warren and Mahoney design, now destroyed. Photo: courtesy of Christchurch Modern.
While around Canterbury all the brick chimneys have been destroyed, it is noticeable how well timber housing has coped with the seismic stresses. Timber, like the trees it comes from, is a flexible, resilient material, and is a good material for saving our cities. Timber can be used as both a material for tension, for compression, and for torsion as well – all the factors needed for resisting seismic quakes. In the picture below, we can see that while the brick and stone facade has collapsed, the timber roof and supporting structure has survived – apparently almost unharmed.
Most of all however, the use of steel seismic resisting frames to construct modern multi-story buildings is showing that it is a quick and strong method of construction, excellent at resisting tension, torsion and compression, and capable of taking great loads without collapse. New Zealand is at the forefront of seismic structural resistance – we have world-class building scientists and engineers working on systems to resist the forces of nature. Recent buildings like Te Papa Tongarewa and the Wellington Hospital are constructed on base isolators that were developed here in New Zealand – by the Ministry of Works in the 1970s – the same Ministry of Works deleted by the government in the 1980s. Even more recent buildings like the MacDiarmid building at the Science Faculty in Victoria University are world class in the extreme. Engineering firms like Dunning Thornton (who undertook the seismic engineering of the MacDiarmid building) have designed a building that can be stiff under normal conditions, but has built-in flexibility to allow movement to relieve the stress – and then spring back into shape when the shake is over, with no permanent structural damage.
What has been especially noticeable in the endless media coverage of the Christchurch Earthquake is the building in the backdrop of both TVOne and TV3 – the Christchurch Art Gallery, designed by Buchan Group, with a glittery, facetted, glass façade. Not a pane appears to have been broken. The building has been once again commandeered to be the headquarters of the Civil Defence force.
The exhibition within (ironically, an exhibition by local architects on how to rebuild Canterbury after the quake) has been pushed aside. The building itself is strongly resilient – far more so, so it seems, than the brand new building for the City Council, which has failed again to perform in some unstated manner.
What is necessary in Christchurch right now is surety in their built surroundings. Mayor Parker has backed the right horse in stating that the Christchurch cathedral should be re-built – as a truly iconic symbol of the City, and missing a stone spire that has killed a score or more of tourists, the Cathedral should arise again. But: not as it was before. The Cathedral needs to proclaim to the city that it is stronger and more resilient than before. Rebuild the city from steel, from modern engineered timber products, from glass in seismic frames and from lightweight materials rather than heavy stone and unreinforced brick. Rebuild the city to the highest standards possible, rather than the lowest standards affordable. Above all: rebuild the city to inspire and reassure the population that our land is safe.