Forgotten Lessons of the past
Following the Christchurch earthquakes, engineering experts have
recommended replacing heavy
Brown was part of Operation Suburb, which involved a team of 400 building inspectors and 300 welfare officers visiting all homes in the affected suburbs to assess damage following the February 22 earthquake. Building inspectors red-stickered any dangerous or uninhabitable homes, and Mr Brown was one of a group of 12 engineers that provided follow-up to further assess borderline, tricky or dangerous structures and land subsidences and confirm or remove the red stickers.tile roofs with lightweight metal roofing. Inspections revealed that extensive damage was caused to houses by chimneys falling through heavy tile roofs or by the tiles coming loose and falling whereas metal roofing generally did not collapse under falling chimneys and was able to withstand the quakes themselves. That was one of the main findings of Wayne Brown, a trained civil/structural engineer and Mayor of the Far North.
Following that work during the first week of March, Mr Brown produced a report to Christchurch Mayor Bob Parker and the Minister of Housing, Maurice Williamson, outlining his findings.
In it, he says: “Simply put house damage fell into some obvious categories and some simple rules were agreed among the engineers that would have reduced the damage cost by billions if they had been in place.
“Flexible structures performed way better than rigid ones and the choice of cladding made a big difference. Earthquake responses are worse with increased structure weight, particularly weight up high.
“Heavy roof tiles and brick chimneys consistently failed and as they fell they created more damage and danger to anyone below. Conversely corrugated iron roofs performed well, even when the chimneys fell as they kept the inhabitants safe. If this had been at night many would have died from falling tiles and chimney bricks. Why not ban both and use iron roofs and steel chimney flues.”
Echoing those findings is a report done 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 co-ordinated science and engineering expertise from across New Zealand.
In a section concerning improving earthquake safety, the report recommends:
“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.”
The report also recommends that larger brick and masonry buildings can be earthquake-strengthened by either internal steel bracing or an external steel frame.
Another report, compiled by Prof Andy Buchanan and Michael
Their report says: “The most common type of damage for older buildings (more than 15 years old) was chimney collapse. This occurred in many thousands of buildings. “Falling chimneys could be interpreted as a violation of the ‘life-safety’ criterion required by New Zealand Standards (NZS1170.5:2004) for current building seismic design. Falli
ng chimneys resulted in damage or piercing of the surrounding roof structure, damage to neighbouring properties, vehicles but (luckily) no loss of life.
“Chimney collapse on to corrugated steel roofing often c
aused no further damage,depending on the height of the chimney, but some fell through the roof or caused rafter failure. Chimneys falling on to tile roofs (concrete or clay tiles, or slate roofs)
more often fell through into the house, sometimes causing further structural damage and potential loss of life.