Christchurch engineering team finds ‘swing’ bridges can be earthquake resistant

A new “swing” design feature could allow New Zealand’s high-strength bridges capable of withstanding natural disasters virtually unscathed.

Experts at the University of Canterbury (UC) have developed a solution based on self-centering vibrating shafts, which allow significant displacement in bridges with little or no damage compared to conventional designs.

University of California professor Alessandro Palermo said the existing bridge design often prevented collapse in the event of an earthquake, but it was not so much damage that it would have taken so long to repair. UCSD experts hope their solution will reduce such damage or allow for quick repairs.

Read more: *Seismic research begins at Foxton’s Whirokino Trestle Bridge site *Canterbury engineering students design collapsible bridges in annual competition *Build a Bridge to Anywhere

The self-centering oscillating shaft consists of two main structural components. One or more high-strength rails that act like rubber bands to update the shaft, and several traditional steel rails designed to dissipate energy and can be easily replaced if damaged.

The research is led by Sabina Piras, a UCSD PhD student and certified bridge engineer, under the supervision of Palermo and Assistant Professor Gabriel Chiaro in the UCSD School of Engineering.

“When an earthquake occurs, the column shakes the foundation,” Beras said.

“The joint in which the swing action occurs is designed and detailed so that it can be easily fixed in a very short time.

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Sabina Piras, a PhD student in engineering at the University of Canterbury, and Professor Alessandro Palermo with their research.

“Repair work can be done on the joint over the course of one night, which prevents significant disruption to traffic, compared to current construction methods that can take months or even years to repair or rebuild.”

The weakness of New Zealand’s bridges has been revealed by recent floods in central Canterbury and the Christchurch and Kaikoura earthquake. In each case, transmission networks were severely disrupted. In the aftermath of the Kaikoura earthquake in 2016, damage, landslides and liquefaction affected more than 900 bridges.

After visiting the area, the researchers understood the need to learn how low-damage swing systems would perform in different soil conditions.

BRADEN FASTIER / Stuff

The inner road between Kaikoura and Wayau after the 7.8 Kaikoura earthquake in 2016.

“The soil on which we build our infrastructure varies a lot across New Zealand and we must understand how additional soil movements in an earthquake affect the oscillating behavior of our shafts,” Beras said.

“The majority of New Zealand bridges are built on single pilings of large diameter, although large and solid, they are still prone to movements in an earthquake. Structural bridge researchers have validated the performance of low-damage vibrating bridge posts by pilot testing assuming that the foundations are stable.

Through their investigations, the researchers developed a new technique for simulating different soil conditions and testing the performance of the swing shaft system.

“We realized that [assumed foundations are fixed in testing] Incorrectly predicts system behavior,” Piras said.

“We are the first to study the effect of soil, foundation and structure interaction on low-damage swing bridge shafts.”

Palermo has worked on several low-damage bridge systems and said, “The main barrier to implementation appears to be the cost and slightly higher risks associated with this new design.”

Joseph Johnson / Stuff

Palermo, in 2019, during the annual UCSD Student Bridge Building Competition, where entries must support two people but fail under the weight of three.

“I consider the Wigram-Magdala Link Bridge in Christchurch to be Tesla Bridges, and I’d like to see more of these seismic solutions in action.”

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