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Rubber: The Life Saver

Scientists believe rubber could help save lives by providing protection from natural disasters. In countries such as New Zealand, that are located on the earth's natural fault lines, earthquakes are a way of life for many people. They have been recorded by the indigenous Māori people for generations, causing a large scale loss of life.

Now, research has revealed how used tyres may be able to provide earthquake protection for buildings. They can be used to provide seismic isolation, a technique that counters the effects of the ground shaking on the buildings' structure, thus protecting them from damage.

House

© Fotolia Premium / Adobe Stock

 

Earthquake history

New Zealand is so prone to earthquakes that they are built into the mythology of the nation. The Māori god, Rūaumoko, is blamed for causing volcanic activity as he walks around below the earth's surface. Many huge earthquakes have been recorded in Māori history, including one at Rotorua said to have claimed the lives of 1,000 people.

Historical evidence suggests two "megathrust" earthquakes (of the type that caused tsunamis in Japan in 2004 and 2011) struck New Zealand beneath the seabed in Cook Strait.

In Wellington, the first significant earthquake experienced by European colonists occurred in 1848. The settlers were unprepared for the quake and its aftershocks, which destroyed a lot of the brick buildings they had constructed. Since then, there have been more than ten major earthquakes in New Zealand.

 

Building regulations

Over the years, the way buildings are constructed has changed to combat the earthquake damage. Prior to 1931, it was believed that large structures built with heavy masonry in urban centres would provide better protection. This appeared to be working - until the massive Hawkes Bay earthquake struck.

On 3rd February 1931, at 10.47am, the earthquake began 15km north of Napier and lasted for 2.5 minutes, killing 256 people and injuring thousands more. There were 525 aftershocks recorded.

Shopfronts and facades fell and the buildings swayed dramatically, before falling down altogether. In tall buildings, the internal floors separated from the walls and the bricks crumbled inwards.

The disaster led to a change in building regulations. The newly-founded Buildings Regulations Committee identified dangerous building practices and introduced new guidelines, many of which developed into today’s building codes.

 

Seismic base isolation

It's difficult to design a building that can withstand an earthquake. While it's less challenging to build smaller structures, making earthquake-proof tall buildings requires a different approach. The building must be able to move a little, while still maintaining its structure.

Recently, engineers have turned to seismic base isolation. The system works by separating the building from the ground via energy-absorbing, flexible, support structures. When the earthquake hits, causing the ground to move, some of the energy is directed into the base isolation structure.

The isolation systems have included heavy-duty springs that will bend and contract, or padded cylinders that will roll when an earthquake occurs.

 

Lead Rubber Bearing

New Zealand engineer Dr Bill Robinson invented the most innovative base isolation system, Lead Rubber Bearing, known as LRB, in the late 20th century.

Robinson, a scientist in New Zealand government laboratories in the 1970s, came up with the idea after talking to Dr Ivan Skinner, his colleague, who was studying base isolators. Robinson worked in solid-state physics and metallurgy. Skinner had been using rubber and steel to experiment in creating base isolators.

The theory was that the steel would absorb much of the seismic energy when it melted and reformed during seismic activity, while the rubber would provide further flexibility. Robinson liked the idea, but felt steel wasn't the best choice of metal.

He studied the Periodic Table of metals to find an alternative and eventually concluded that lead was the best choice. He then began to design a new device, using lead and rubber and making the most of all their properties. It worked in a similar way to a car's suspension.

 

Giant shock absorber

He first released his LRB design in 1975. He made pillars from laminated layers of steel and rubber around a central core of lead. The rubber acted like a giant spring that would reform back into shape after each shock from an earthquake.

This "sandwich" design created a giant shock absorber, which could stretch sideways when the ground shook. The design stopped most of the earthquake's energy from passing through the building. Its unique properties have made the LRB system the most popular design for earthquake protection.

The system has spread from New Zealand across the world and it's used in more than 8,000 buildings. It is also used in rail and road bridges. The system can't make a structure completely earthquake-proof, but it minimises the damage, protecting people from injury.

In Kobe, Japan, the LRB-protected Telecommunications Computer Centre survived when the 1995 earthquake struck, destroying most of the surrounding buildings. In the United States, the University of Southern California Teaching Hospital not only survived the 1994 Los Angeles earthquake, it could also remain operational.

 

Saving lives

Robinson, who died in 2011, saved many lives thanks to his innovative design. His system was also widely used in the rebuilding of Kobe and Los Angeles following the earthquakes.

In New Zealand, the LRB system was installed during construction of the Te Papa Tongarewa Museum, which opened in 1998. The structure is supported by 152 LRB bearings. They can also be retro-fitted in older existing structures that are deemed at risk.

In 2018, a group of scientists at the University of Canterbury in New Zealand received a $1 million government grant to find ways of making the LRB system cheaper to install.

In a report entitled, "Eco-rubber Seismic-isolation Foundation Systems", they suggested using waste tyres to make the LRB. Used tyres are already recycled, but the report suggested they could be used to build safer buildings too.

 

Recycling tyres

Leading the research, Dr Gabriele Chiaro said five million tyres reached the end of their life in New Zealand each year. He claimed 70% of them were still going to landfill sites, or were being stockpiled or disposed of in some other way, so waste tyres remained a problem.

As a source of high-quality rubber that can be used in base isolation systems, the team at Canterbury has come up with a different design from anything currently available. Their eco-rubber foundations don't look like the original flexible pillars. They are solid, steel fibre-reinforced, rubberised concrete rafts, on top of a thick layer of a mixture of waste rubber and gravel.

Fellow scientist Prof Alessandro Palermo, Chiaro's colleague, is developing the raft, which sits directly underneath the building and acts like a traditional foundation.

 

Crack-proof material

The rubberised concrete is less prone to large cracks. Tiny steel fibres act as a micro-reinforcing material to hold the mix together, preventing even the tiniest cracks from forming.

Scientists are conducting further research to discover the best combination of waste rubber and the other materials. Although the research has been up and running for just one year, it's already "moving fast", according to the scientists involved.

For a wide variety of high-quality rubber products, including rubber matting, extrusions, seals, etc., give Coruba a call on 01702 560194.



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