A new “rocking” design feature could allow for high-strength bridges in New Zealand able to withstand natural disasters almost unscathed.

Experts at University of Canterbury (UC) have developed a solution based around self-centering rocking columns, which allow for large displacements in bridges with little to no damage compared to conventional designs.

UC professor Alessandro Palermo said current bridge design often prevented collapse in an earthquake but not significant damage that was time-consuming to fix. The UC experts hoped their solution would minimise such damage, or allow for rapid repairs.

A self-centring rocking column comprises two main structural components. One or more high strength bars that act like rubber bands to recentre the column, and several conventional steel bars designed to dissipate energy and be easily replaceable if damaged.

The research is being led by UC Civil Engineering PhD student and chartered bridge engineer Sabina Piras, under the supervision of Palermo and associate professor Gabriele Chiaro at UC’s College of Engineering.

“When an earthquake occurs, the column rocks over the foundation,” said Piras.

“The joint where the rocking motion happens is designed and detailed that it can be easily repaired in a very short time.

“The repair work on the joint could be done over one night closure, preventing major traffic disruption, in comparison to current construction methods that can take months or even years to fix or rebuild.”

The vulnerability of New Zealand’s bridges has been exposed by the recent flooding in mid-Canterbury and the Christchurch and Kaikōura earthquakes. In each case, transport networks were severely disrupted. Following the Kaikōura earthquake in 2016, damage, landslides and liquefaction affected more than 900 bridges.

After visiting the area, the researchers understood the need to know how low-damage rocking systems performed in different soil conditions.

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