Best seismic protection for new buildings a must

All-new or replacement buildings in New Zealand should make use of state-of-the-art seismic damage-resistant technology, according to a structural engineer at Canterbury University, Associate Professor Stefano Pampanin.

A post-tensioned shear wall being installed at the Carterton Events Centre

“Current technology will not only protect people from earthquake damage, it is designed and tested to suffer minimum or no structural damage itself,” Dr Pampanin says.

Based on his experience of the rebuild after the 2009 L’Aquila earthquake in Italy, Dr Pampanin has very clear views on the standards that need to be applied to the reconstruction of Christchurch.

“We have technology capable of doing fantastic things nowadays, and it would be unacceptable if we were not implementing it.”

Ten years’ difference

Over the last few months, Dr Pampanin has been busy assessing and investigat - ing the extent of damage in multi-storey buildings in Christchurch’s CBD. He attaches no blame to the severe damage of buildings that were based on the best seismic engineering principles known at the time.

“People in 1960 were undoubtedly very smart and competent – they knew a lot for that time. They thought they were doing it [building] in the best possible way. But just ten years of further research, testing and earthquake experience was enough to improve the knowledge – the building codes in New Zealand change and improve significantly every ten years. In 50 years’ time, people will be smiling at us, saying ‘they didn’t know’. Obviously we don’t know what we don’t know.”

However, Dr Pampanin says there can be no excuse for not designing and building with the best safety systems avail - able to us today. He doesn’t have firm views on whether that rebuilding should make use of the now popularlyfavoured wood solution over traditional materials such as concrete or steel.

“All of them can perform equally superbly with current damage-resistant technology,” he says. “The benefits of different material should actually be exploited in combination – that’s a win-win outcome.”

Hybrid seismic solutions

Dr Pampanin has been a strong advocate and key driver for the application of the latest seismic safe concrete technology (precast seismic structural system, or PRESSS, based on rocking prefabricated systems connected by post-tensioned tendons) in New Zealand and its extension to a New Zealand-designed timber version, known as Pres- Lam (prestressed-laminated timber).

He believes hybrid solutions also make sense. For instance, the timber Pres-Lam system can be integrated with concrete or steel-concrete floors and the acoustic advantages they offer. Concrete-filled timber or steel columns, CFT, could be used for high-rise buildings, combining the advantages of timber and steel with the compression strength of concrete. The beams could be all timber using LVL (laminated veneer lumber).

“You can have either post-tensioned concrete or post-tensioned timber for shear walls and frames, or you can merge them together. You can add steel-based energy dissipater devices or braces. The important thing is to raise the bar for the whole industry.”

Costly repairs

Buildings designed in the 1980s were designed with deformable connections (or plastic hinges) in the beams to dissipate seismic energy, protecting the building from failure and collapse. Generally, these features worked exactly as intended in the Christchurch quakes. Failures were averted and lives were undoubtedly saved.

However, repair costs to restore the buildings will be significant, Dr Pampanin says. “It’s going to cost millions of dollars to repair – nowadays you can design buildings that can survive earthquakes without a single scratch.”

While originally Dr Pampanin’s engineering experience focused on reinforced and prestressed concrete, he has also become a convert to the advantages of advanced timber materials or engineered wood, such as Glulam, LVL, Crosslam and Pres-Lam.

In seismic engineering terms, timber has a natural weight advantage – having a lower mass means it is affected less by shak - ing, and does not place the same demands in terms of foundations, particularly in soil that may be less than ideal. This advantage can balance the inherent lower strength and stiffness that timber can offer when compared to concrete and steel.

“Timber is not only sustainable and green, but if you’re using the technology available in 2011, it is up with the best in the industry,” Dr Pampanin says. “This doesn’t mean it’s better than concrete or steel, but it is equally able to perform to the highest standards.”