Researchers in New Zealand have put forward a “low-damage” design as an alternative for earthquake-resilient for bridges.
“Current earthquake design philosophy prevents the collapse of bridge infrastructure as a result of a large-magnitude earthquake, but that does not mean that bridges won’t be significantly damaged,” said University of Canterbury College of Engineering professor Alessandro Palermo, who is working on the project with civil engineering PhD student and charted bridge engineer Sabina Piras (both pictured above) and associate professor Gabriele Chiaro.
He added: “Road closures and repairs can have a significant social and economic impact as seen in the Canterbury and Kaikōura quakes, which brought the affected regions to a standstill and cost the economy millions.”
The team have developed a solution which, through the combination of self-centring rocking bridge columns, can achieve large displacements with little to no damage compared to conventional bridge columns. A rocking column is comprised of two main structural components: one or multiple high strength bars that act like rubber bands to recentre the column, and several conventional steel bars that are detailed to dissipate energy and can be easily replaced if heavily damaged.
“When an earthquake occurs, the column rocks over the foundation. The joint where the rocking motion happens is designed and detailed such that it can be easily repaired in a very short time,” says Piras. The repair work on the joint could be done over one night closure, preventing major traffic disruption, she says, in comparison to current construction methods that can take months or even years to fix or rebuild.
The work was inspired by the 2016 Kaikōura earthquake which had a major impact on the transport network with damage, landslides and liquefaction affecting over 900 bridges. After visiting Kaikōura, the researchers understood the need to know how low-damage rocking solutions perform in various soil conditions. “It’s like driving a Ferrari on the road or rough terrain; its performance will not be the same,” said Palermo.
The researchers investigated the influence of different soil types on the low-damage rocking column system and developed a novel and simplified testing technique to simulate this complex problem.
“The soil we build our infrastructure on varies so much throughout New Zealand, and we must understand how additional soil movements in an earthquake influence the rocking behaviour of our columns,” said Piras.
“The majority of New Zealand bridges are built on single, large-diameter piles that, although big and stiff, are still susceptible to movements in an earthquake. Structural bridge researchers have validated the performance of low-damage rocking bridge columns through experimental testing assuming that the foundations are fixed. However, we have recognised that this incorrectly predicts the behaviour of the system, and we are the first to study the influence of soil-foundation-structure interaction on low-damage rocking bridge columns.”
According to the research team, the novelty of the solution stands on its simplicity to build.
“I have worked on several different, low-damage bridge systems and it seems the main barrier to implementation has been the slightly higher cost and risk associated with this novel design,” added Palermo. “I consider the Wigram-Magdala Link Bridge in Christchurch the Tesla of bridges and would like to see more of these seismic solutions being implemented.”
The team said that its research expands on past projects and application of post-tensioned rocking bridge columns but has focused on developing a cost-effective solution with the aim of getting clients, consultants and contractors to start adopting the approach more quickly.
Department of Civil Engineering https://www.ibu.edu.ba/department-of-civil-engineering/