ANALYSIS Spending boost presents upgrade opportunity for bridges All bridges have finite lifespans. Many are now carrying greater loads than they were ever expected to, and bearing maintenance is important to longevity Government infrastructure spending boosts following the Covid pandemic may provide a welcome opportunity to upgrade many of Australasia’s 57,000-plus bridges, many now handling loads they were not originally expected to carry. The opportunity for maintenance is particularly significant for Australasia’s local roads network, involving some 30,000 bridges in Australia, most small to medium, many built before 1950, and some before the turn of the century. It is also significant for the 4200 bridges on State And Federal Highway networks, including the 4200 for which the NZ Department of Transport is responsible, including 185 of which are single lane and the oldest of which, the Waianakarua South River Bridge, in North Otago, which was built in 1868.
and cooling expansion and contraction in a bridge structure have to be planned into structures decades ahead. All bridges are an expensive asset with a finite lifespan, so it is common sense and safety planning to factor in the foreseeable,” says Mr Booty, who is Manager of Hercules Engineering (a division of Cut To Size Plastics). The challenge facing builders and operators of thousands of smaller bridges and aqueducts throughout Australasia is ensuring how concrete and steel structures can flexibly, quickly, and cost-efficiently cope with internal movement and stresses caused by changing loads, vibration, thermal expansion, and other common attritional factors.
“Public authorities who manage most of these typically smaller bridges have long been aware of the problem facing our road transport infrastructure, but haven’t had the funds to do the work they would like to. Now they have the opportunity to list their preferred projects with the Government so as to extend the safety and lifespan of assets,” says bridge sliding bearing producer Mr David Booty. Mr Booty has more than 40 years’ experience in the assessment and life-extending renovation of bearings supporting public and private concrete and steel bridges and accessways, accommodating changing loads and demands upon them. He says the engineers responsible for bridge management would often like to do such work for safety and productivity reasons, knowing that trucks and utility vehicles of all types today are a vital link in our rural and urban infrastructure.
bonded to a mild steel or grade 316 stainless steel base plate. “Among the big plusses of HLD Bearings, compared with more sophisticated and expensive heavy alternatives such as pot bearings and roller bearings, are benefits such as lower initial cost, easier installation and no maintenance for periods of 30 years or more,” says Mr Booty. “Larger bridge structures demand sophisticated and typically more expensive solutions, but HLD bearings are very suitable for a wide range of bridge, materials handling, and process equipment structures up to 60 tons per bearing.” The evolving range of Herculon type D sliding bearings – incorporating polymers proven globally for outstanding durability without lubrication or maintenance – were developed to fulfil the need for low-friction bearings on corbels and columns where continuous sliding joints were not appropriate. Aqueducts also are expensive assets, and they can have their foundations weakened if bearings fail in their job of protecting against thermal expansion and contraction and load changes
No-maintenance performance Stock Type D Herculon Bearings (HLD/SG) are designed to accept a lateral load of 30 per cent of the vertical rated load, which can be up to 600 kN per bearing in stock sizes, with higher capacity available custom-engineered for particular applications. They are removable and replaceable, to optimise no-maintenance performance in access infrastructure and high output industrial plant. The ability to provide cost-efficient and maintenance-free solutions to such issues is especially important to road and pedestrian access projects demanding high safety.
Herculon Type D bearings In addition to public bridges are engineered to minimise handling road transport, such downtime and maintenance structures include private by accommodating the vertical assets, such as those providing and horizontal stresses imposed When these cars and trucks were on the roads of Australasia in the 1950s, loads on bridges supply, exploration and service by the shuddering and vibration of were lighter because vehicles – especially trucks- generally were smaller and lighter. routes to mining, energy, oil and varying loads gas projects, where movement “But many of the larger trucks out within access structures is caused there today weigh far more than by factors such as climate, changing uses and delivery One solution developed by Hercules Engineering the 30-odd tons that was considered appropriate of plant including conveyors, motors, turbines and comprises the range of no-maintenance, for short-to-medium bridges up until the mid-70s. reticulation systems. cost-efficient Herculon Type D Bearings (HLD/ And not only are all vehicles generally heavier – cars, SG, HLD/FF & HLD/FX), which are widely proven utes and trucks – but also the number of individual Asset life-extending maintenance solutions are also on applications ranging from steel and concrete vehicles on the roads has increased vastly since then. important to access facilities in urban infrastructure beam engineering structures through to materials projects, including pedestrian walkways, small “This adds considerably to the changing loads and handling and processing facilities. bridges and health and carpark facilities. vibration resulting from generally bigger vehicles Herculon Type D Bearings (HLD/SG) consist of a and more of them.” Herculon HLD bearings are part of a comprehensive mild steel or 316 stainless steel top plate to which range of Hercules composite sliding joints and a polished stainless steel facing plate is fixed. This Climate change structural bearings incorporating engineered plate slides against a low friction hard-wearing high performance combinations of engineered “Now, climate change also has to be factored into (PTFE) Hercuflon-coated Hercupad, which is in turn sliding bearing design, because the rates of heat thermoplastics and stainless steel facing surfaces.
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NZ Manufacturer August 2020 /
www.nzmanufacturer.co.nz
