Cost-efficient polymer shock blocks offer 100 years of concrete bridge protection against earthquakes in Australia and New Zealand

All bridges have finite lifespans. Many are now carrying greater loads than they were ever expected to, and earthquake protection is important to longevity

Lateral restraint blocks made of an engineering plastic that typically retains most of its strength over 100 years are being produced by Hercules Engineering to safeguard suburban and highway concrete bridges against earthquakes and radical structural movement.  

The custom-fabricated high density polyethylene PE 100 blocks are used as sacrificial elements so concrete components will remain preserved instead of grinding on one-another, says bridge bearing producer Mr David Booty, Manager of Hercules Engineering (a division of Cut To Size Plastics). 

Apart from minimising sliding wear, HDPE blocks can also minimise the impact of shock by deforming and absorbing the kinetic energy that could otherwise fracture or destroy single span beam bridges spanning creeks, hollows and smaller obstacles, potentially causing accidents, human casualties, disrupting vital communications and costing time and money to restore, says Mr Booty. 

An earthquake exceeding magnitude 7 occurs somewhere in Australia every 100 years or so, according to Australia’s Seismology Research Centre, while nations on the Pacific “Ring of Fire” earthquake zone (including New Zealand, SE Asia, Japan and the American West Coast) experience them far more regularly, sometimes several a year. Even relatively smaller earthquakes – such as the magnitude 5.6 Newcastle earthquake – can cause extensive damage. The 6.3 magnitude Christchurch earthquake was one of New Zealand’s worst-ever disasters, because it also struck close to a populated area.

David Booty, right, with Laurie Green, the Managing Director of Cut To Size Plastics, of which Hercules Engineering is a division. The company has installed some of Australia’s most efficient and versatile engineering plastics technology to produce precision plastics components.

“Bridge builders – including public works and private enterprise – are very aware of their Duty of Care to safeguard their structures’ safety so we had approaches to see what we could recommend as the best long-term, simple and cost-efficient solution. It turned out the PE100 blocks were not only the best polymer available for the job, but also one of the least expensive,” said Mr Booty, whose company produces a range of bridge bearings that are in strong demand as bridges cope with the expanded loads they have to carry on public and private roads, including those serving resource, construction and civil engineering sites. 

The easily handled and installed PE100 virgin grade HDPE blocks – the latest order for which was 200x200x40mm blocks for a Sydney suburban bridge – are made from the same long-life material from which HDPE water pipes are made.  

Custom-shaped PE100 can be readily shaped for particular uses where its long life and non-permeability is essential, including piping, bridge blocks and tanks for water and processing fluids

This well researched long-life material has been tested by the International Technical committees responsible for ISO and EN standards. HDPE can be welded, does not absorb moisture, does not crack when water is frozen solid inside and can tolerate deformations without cracking. PE 100 can retain 60 per cent of its mechanical strength at average ambient temperatures of 20oC for up to 100 years and potentially more, depending on the application.  

Even higher performance composite materials are available from Hercules Engineering, which also produces Stainless Steel–PTFE–Elastomer Bearings to enable concrete and steel structures to flexibly, quickly, and cost-efficiently cope with internal movement and stresses caused by changing loads, vibration, thermal expansion, and other common additional factors. 

One solution developed by Hercules Engineering comprises the range of no-maintenance, cost-efficient Herculon Type D Bearings (HLD/SG, HLD/FF & HLD/FX), which are widely proven on applications complementing the PE100 blocks, ranging from steel and concrete beam engineering structures through to materials handling and processing facilities. Herculon HLD bearings are part of a comprehensive range of Hercules composite sliding joints and structural bearings incorporating high performance combinations of engineered composite materials and stainless steel facing surfaces.