Engineered system a lifeline for state’s deteriorating timber bridges

Thirty per cent of timber bridges in regional NSW are in a poor condition, making the restoration of these critical transport arteries a priority for local governments and councils.

Given the importance of these transport routes and the safety of the local community, councils have needed to lower payload and speed limits as a precaution to the continued deterioration and disrepair of the state’s 2,000 timber bridges.

When a bridge is closed for maintenance or repairs, or is load limited, the impact on the local community can be significant, particularly if the bridge is one of only a handful of access points crkconnecting a region, as is the case with the farming area around Cedar Creek Bridge in NSW’s Hunter region.

As one of 74 bridge assets in the Cessnock local government area, the ageing timber bridge was highlighted as a priority for urgent restoration given the significant deterioration of the corbels, girders and deck planks. “Heavier vehicles cause much more vibration in the bridge as they pass over, this can cause bolts and fasteners to rattle loose over time requiring higher maintenance and causing increase wear to the joints in the timber,” explains Justin Fairfull, Cessnock Council Bridge Inspector. The council had implemented a six-tonne load limit on the bridge as a short-term solution while it searched for a low-cost alternative to a steel or concrete replacement, both of which come at significant costs to the community.

Bridges form a vital part of Australia’s transport network, with around 30,000 timber road bridges in service throughout the country. In NSW, timber bridges are recognised for their place in the state’s colonial history, with many of the old bridges classified as ‘State Significant’ under the Heritage Act. However, heavier and faster moving vehicles have put a considerable strain on these old timber bridges, accelerating the rate at which many of these ageing timber structures have been deteriorating.

As a way to extend the life of timber bridges, the Cessnock Council selected Bridgeply, a plywood bridge deck system developed by timber specialist and plywood manufacturer, Big River Group. An alternative to steel and concrete decks, the system is an engineered substitute for traditional hardwood decking, which is less expensive and faster to install, a critical measure of success for the Cedar Creek Bridge.

“The larger size of the Bridgeply product helps to absorb much of the extra vibration of heavy vehicles while also tying together the other timber components of the bridge better than solid hardwood planks,” says Fairfull. “So the product is not only quite durable in itself but it also extends the life of the timber frame it’s installed on.”

As Fairfull explains, due to the condition of the bridge and the local community, comprising of small farms, a bed and breakfast, and a wombat refuge, who needed access to this infrastructure, a fast installation to minimise the impact on the residents was critical.