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Earthquakes usher in new era for steel construction in New Zealand

Steel News - Published on Wed, 17 Jan 2018

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Christchurch's earthquake experiences have ushered in a new style of architecture that has influenced construction in Wellington and raised awareness in Auckland. Steel construction is the biggest and most obvious feature in the city's buildings for the cost as well as safety perceptions. The earthquake rebuild has also changed the relationships between professionals in the sector with early discussions on a project usually beginning with engineers rather than architects.

Typical post-2011 earthquakes steel framing construction in Christchurch with reinforced concrete slab walls.

The construction response to the earthquakes is the subject of a 170-page report by co-authors Michel Bruneau from the University of Buffalo, and Greg MacRae, a professor at the University of Canterbury in Christchurch.

They spoke with professionals involved in new construction in Christchurch and surveyed 74 buildings, which made predominant use of steel frame construction.
Steel has been used in refurbishments of existing buildings as well as new ones, post-earthquakes.

Steel has been used in refurbishments of existing buildings as well as new ones, post-earthquakes.

Some examples of steel framed buildings already existed at the time of the earthquakes the former HSBC Hse in Worcester Boulevard, and the Rendezvous Hotel. They stood up well.

"All engineers met stated that, while the 2010–11 Christchurch earthquakes were a wake-up call to communities in the Wellington area, the 2013 Seddon earthquakes, and particularly the 2016 Kaikoura earthquakes, reinforced the message."

A change in client perception also occurred in Auckland, but "there is still inertia there".

Christchurch's earthquakes were a "watershed event" because although engineers knew the risks, clients did not.

"Prior to the earthquakes, the architect would develop the conceptual plans and ask the engineer to fit a structural system to it. Now, structural and geotechnical engineers are brought into the project at the same time as the architect, or sometimes sooner. However, a number of engineering firms have stated that client awareness is slowly fading as the years push the earthquakes further in the past.”

The researchers said that while reinforced concrete buildings behaved as designed and mostly protected lives, the concrete connections, precast elements, and stairs were extensively damaged and often too expensive to repair.

As a result, owners wanted more cost-effective, fast to build, and reparable buildings, so engineers came up with braced steel structures which architects embraced, and the braced frames often replaced the concrete shear walls that make up the strongest element of a building.

Steel braced structures also allowed lightness and flexibility, especially with open-plan work places.

"For these reasons, braced frame buildings are spreading across the country."

The lighter steel riveted and welded framing had been used from 1910 until the 1970s when industrial action curtailed its widespread use and reinforced concrete construction dominated, although steel was making a comeback by 2009.

The increasing use of steel by 2010 was partly due to price. In mid-2008, the price of steel peaked at a record high of US$1265 per metric ton and quickly decreased by mid-2009 and has fluctuated since with prices less than half of the peak 2008 value."

But there had been significant quality issues with imported steel from Asia, also reported in Australia and the UK.

"As a result, some engineers and contractors will only allow the use of structural steel that is sourced locally or from pre-approved overseas mills. Others will rely on extensive testing to ensure quality."

Even so, the perception from the public and tenants that steel was a superior form of construction had been a major part of the Christchurch reconstruction. Concrete gravity systems were rarely seen now in Christchurch, the report said.

Steel construction and base isolation became marketing features for most rebuilds, even though there are higher costs from the additional floor slab needed above the isolation level when there is no basement or underground parking.

Engineers from structural firms told the researchers that steel structures made quality assurance easier because the frame is on display, particularly with bolted connections

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Posted By : Nanda Koijam on Wed, 17 Jan 2018
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