Timber alternatives ease earthquake concerns

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Building Alternatives More WoodThe experience of rebuilding the Italian town of L’Aquila after its devastating earthquake in 2009 showed people who have been through such disasters have a preference for timber, according to Italian engineers.

Engineer Paolo Lavisci from the Society of Engineers in Italy said the people in L’Aquila "were asking for no more concrete" immediately after the earthquake.

Since then, the use of wood in construction has taken off in Italy. "Now we have completed designs for six and eight storeys and are designing for 12 storeys for large ‘traditional’ building companies who just a year ago would never even commission a timber house."

The shallow 5.8 magnitude earthquake killed 308 people, destroyed up to 11,000 buildings and left 65,000 of the medieval town’s population of around 100,000 homeless.

Mr Lavisci’s company won a tender, along with several other contractors, to build a number of three storey, 27-apartment blocks using timber. Their construction took only 72 days – and only 14 days for the erection of the watertight outer shell.

Made from cross-laminated timber sections, the completed block weighed around 430 tonnes compared with what would have been more than 2000 tonnes in concrete.

The lower mass weight of a building, can lessen the damage sustained from earthquakes.

Dr Geoff Thomas from Victoria University’s School of Architecture says earthquake loads or forces on a building are also proportional to its weight.

"A timber building, typically lighter than a brick, concrete or steel building, therefore induces lower earthquake loads."

Being inherently lighter and more flexible, timber buildings need not be as strong as a more rigid structure in order to resist the same level of earthquake shaking.

"In the event of a collapse, survival is much more likely in timber buildings as the lower weight of any falling debris from the structure is less likely to cause serious injury than that of heavier materials," Dr Thomas says.

"Understanding these facts has resulted in better building design which saved many lives in the Christchurch and other earthquakes around the world."

Dr Thomas said that timber buildings of six stories or more are now being designed and built to resist earthquake loads. 

A team of University of Canterbury researchers Alessandro Palermo, Andy Buchanan and Stefano Pampanin invented in 2005 an innovative "Pres Lam’ seismic system, which uses laminated veneer lumber (LVL) to form large shear walls which are post-tensioned to the ground using embedded high-strength steel rods, which have been tested to withstand earthquake loads.

The $6 million Carterton Events Centre, used this system.

Opus senior structural engineer Dave Dekker said the Pres Lam system allowed walls to rock back and forth in an earthquake, absorbing earthquake energy as they move.

"It significantly reduces the amount of movement and damage to a building during an earthquake, meaning fewer repairs for the building after a large quake, not to mention overall safety.

"The design of the post-tensioned rods causes the building to return to a vertical position, rather than to the angle the building happens to be at once the shaking stops."

The post-tensioned LVL system was developed as an alternative to the same system constructed in concrete.

Just north of the centre of London is the world’s tallest modern-timber residential building. It stands at nine storeys, the top eight being constructed from cross-laminated solid timber.

The building is the first of this height to construct load bearing walls and floor slabs as well as stair and lift cores entirely from timber.

Each panel is made up of five layers of timber crossing each other, making a panel that could be compared to precast concrete.

Doors and window openings are pre-cut into the panels during manufacturing and the panels arrive at site in lengths up to nine metres long. Assembled using cordless drills, there were only five people on site and they worked only three days a week. The building was completed within 49 weeks.

Plumbers and electricians installing the pipe supports and cable trays suspended under the floor had no worries about concrete dust or the time it took to install a fixing. The panels had passage ways within the panels to feed cables and services through.

Other cost savings were achieved as there was no need to build a basement to house the plant for the renewable energy component, saving time and holding costs.

Architect, Andrew Waugh says that the "overall cost was much the same as for a steel or concrete building."

Timber was used partly because of a City of London planning requirement for a 10 percent reduction in carbon through on-site renewable energy generation.

This building is a result of the practice’s research in reducing the carbon emissions, not only of the finished building but of the whole build process.

Waugh Thistleton Architects estimate the wooden structure of the building will store over 186 tonnes of carbon for its lifetime.

By not using more traditional concrete building techniques, a further 125 tonnes of carbon is saved from entering the atmosphere. They anticipated carbon emissions saved from a building of this size to be the equivalent to 21 years of use.

For more information, contact:

Brian Langham, NZ Wood

Tel: 021 784 626

E-mail: [email protected]

Paolo Lavisci

Society of Engineers, Italy

Tel: +39 335 213568

Email: [email protected]

Geoff Thomas

Victoria University

Tel: 04 463 6247

Stefano Pampanin

University of Canterbury

Tel: 03 364 2249 ext 6249

E-mail: [email protected]

Alessandro Palermo

University of Canterbury

Tel: 03 364 2987, internal 8867

E-mail: [email protected]

Andy Buchanan

University of Canterbury

Tel: 03 364 2987 ext 6243

Email: [email protected]

Andrew Waugh

Waugh Thistleton Architects

United Kingdom

Tel: 44 20 7613 5727

Visit: www.waughthistleton.com

Stradthaus project video via: http://www.nzwood.co.nz/case-studies/murray-grove-tower/

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