Adelaide City Council this week released a tender for a structural investigation of the nearly 100-year-old concrete arch bridge which carries more than 30,000 vehicles a day between Adelaide and North Adelaide.

Built between 1929 to 1931, the nine-lane bridge on King William Road is now suffering from “historic overloading and insufficient waterproofing”, according to the council tender.

“Recent condition inspections indicate Adelaide Bridge shows signs of deterioration and reduced asset life,” the tender states.

“A level 2 condition inspection undertaken in 2022 estimated Adelaide Bridge should be replaced or undergo extensive strengthening and remediation works within five years.”

The Adelaide Bridge opened in 1931 and was added to the state heritage register in 1986. Photo: Thomas Kelsall/InDaily

Council’s long-term financial plan lists the cost of undertaking a “significant asset renewal” of Adelaide Bridge at $63m.

The council is now seeking a report on the costs of pursuing an upgrade or full bridge replacement.

It has also asked the contractor to consider upgrade/replacement options that accommodate a tram extension to North Adelaide, stating that the current structure is not strong enough for trams.

Adelaide Bridge is nine-lanes and 40-metres wide. Despite this, council has highlighted concerns about its use on Adelaide Oval matchdays. Photo: Thomas Kelsall/InDaily

“With the projected ongoing deterioration of the Bridge as it approaches end of life, the deferral of a full bridge renewal or replacement could lead to individual components deteriorating to an unsafe level,” the tender states.

“Should any individual arch, column, cross beam, longitudinal stringer, or deck slab elements reach an unsafe condition, costly reactive repair works would be required to return the structure to a safe condition until the bridge structure is replaced or significantly rehabilitated.

“There is potential for the Bridge to reach a point where it is no longer economically feasible to undertake these restoration activities to keep the bridge at a structurally safe level and further restrictions or bridge closure may need to be considered.”

The interior structure of Adelaide Bridge. Photo: Thomas Kelsall/InDaily

In 2019, a 26-tonne load limit was introduced to protect Adelaide Bridge from heavy vehicle traffic.

That came after a load-rating study in 2016 found the bridge “had half the capacity of current standards”.

The council tender notes broader concerns with the nine-lane bridge’s current use, including its capacity when there are major events at Adelaide Oval.

“Currently, the Adelaide Bridge is not meeting desired levels of service, with heavy vehicles restricted and on Adelaide Oval event days, pedestrian loading is spread onto the road surface and buses are not allowed to bank up on the deck.

“Additionally untreated stormwater drains from the bridge deck into the river Torrens below.

“There is also the potential for Adelaide’s tram network to expand and continue north along King William Road into North Adelaide, the increased loading of a tram crossing is not feasible with the current bridge’s strength and would require increased capacity as part of an option to facilitate trams.”

The former Weatherill Government made a $259m election promise in 2018 for a tram extension to North Adelaide from King William Street to O’Connell Street, but the plan was scrapped when the Liberal Party won government.

Among the options the council has asked the future contractor to investigate for Adelaide Bridge are:

• Continue Current Corrective/Targeted Maintenance.
• Strengthening and Condition component/full Renewal (with load limits).
• Retention of Heritage Elements/Façade and Replacement of Trafficable Bridge.
• Full replacement with a modern equivalent Bridge.
• Full replacement with Heritage features/Replication.
• Full replacement modern bridge with Tram capability.
• Full replacement Heritage feature bridge with Tram capability.

The council tender says it is “imperative to cost-effectively manage” the upgrade so “both current and future levels of service expectations are met. Most notably, the potential increased capacity for the tram network extension along King William Street and across the Adelaide Bridge”.

Adelaide City Council declined to comment on whether it would be asking for state government funding help for the project.

The report on the bridge upgrade/replacement options is due in May 2024.