Mt Crosby’s heritage-listed Weir Bridge in Queensland has been decommissioned and repurposed into a pedestrian bridge featuring a Fibre Reinforced Polymer (FRP) collapsible handrail system designed to protect the structure during flood events.
This project balances preserving historical infrastructure with innovative design solutions to improve flood resilience and pedestrian access.
For Pensar Project Engineer Sam Strofield, it marked his first experience with decommissioning and repurposing infrastructure.
“The project involved the decommissioning of a heritage-listed road bridge, originally constructed circa 1926, and repurposing as a pedestrian bridge,” Sam Strofield said.
“The bridge, once used for vehicular traffic, had become unsuitable for modern use due to its 9-tonne load limit and narrow width, which did not support two-way traffic,” Mr Strofield said.
“With a modern traffic bridge constructed parallel to it, repurposing the original structure for pedestrian use was the most practical and sustainable option,” he said.
“The scope included the removal of the existing balustrade system and replacement with a new, aesthetically improved design. A footpath was also constructed to provide pedestrian access to the bridge.”
“The balustrades were designed with functionality in mind, specifically to support Seqwater operations during flood events.”
Pictured – Weir Bridge featuring the FRP handrail system parallel to the new road bridge.
With flood risk being a key consideration, engineers implemented a smart, collapsible Fibre Reinforced Polymer (FRP) handrail design to protect the bridge during extreme weather events.
“Given the region’s position along the Brisbane River, the handrails were designed to be collapsible,’ Sam Strofield said.
“In anticipation of a flood event, Seqwater’s Operations team can remove locking bolts from the handrail base plates, allowing the handrails to be lowered flush against the bridge deck. Once lowered, tensioned cable secures them in place,” Mr Strofield said.
“This innovative design minimises the potential for damage from fast-flowing floodwaters and floating debris,” he said.
“By reducing the vertical profile of the balustrades, the risk of structural impact and debris accumulation is significantly lowered.”
“To integrate the FRP handrail with the existing bridge structure, we mounted each handrail onto a galvanized stainless steel base plate.”
“These plates were then secured using the original hold-down bolts embedded in the bridge deck.”
“This approach ensured compliance with heritage constraints while providing a stable and secure installation platform.”
Pictured – The FRP collapsible handrail system laid down.
Installing FRP at this scale was new territory for Pensar, but the material’s advantages quickly became clear.
“Pensar has had some experience working with FRP however not to this scale,” Sam Strofield said.
“Despite it being a proprietary design, the FRP components were delivered prefabricated and ready for installation,” Mr Strofield said.
“We found them easy to work with and lighter than steel, which improved manual handling and installation efficiency,” he said.
“Their corrosion resistance is a major advantage, especially in environments exposed to moisture or chemicals, reducing long-term maintenance.”
“The FRP installation process was broadly similar to working with traditional materials like steel or aluminium, but the key benefit was the ease of handling due to its lighter weight.”
“This reduced the need for heavy lifting equipment and improved site safety and efficiency.”
Pictured – The Pensar team installing the FRP handrail system.
Working with a heritage-listed bridge presented unique challenges during the balustrade installation.
“The bridge deck, being almost a century old and heritage listed, was uneven and could not be modified,” Sam Strofield said.
“This meant we had to work with the existing hold-down bolts, complicating the alignment and installation of the new balustrades,” Mr Strofield said.
“Achieving a straight and level handrail alignment required creative solutions within tight constraints,” he said.
“As we were also working over waterways, careful action was taken to prevent materials, tools, or debris from falling into the water, which could have adversely affected aquatic life and water quality.”
Pictured – The 99-year-old original bridge and the new two-lane road bridge called ‘Explorers Bridge’.
The innovative handrail design offers a practical solution for flood resilience while making a strong case for wider use of FRP in future projects.
“The collapsible handrails provide a proactive flood damage mitigation strategy,” Sam Strofield said.
“By allowing the handrails to be lowered in advance of a major flood, the design significantly reduces potential damage to both the handrails and the bridge structure,” Mr Strofield said.
“This functionality also reduces debris buildup during flood events and simplifies post-flood recovery,” he said.
“Additionally, the lighter FRP material makes operation easier and quicker for the asset owner, particularly when time is critical.”
“This project highlighted the value of considering FRP components as an alternative to traditional materials.”
“The benefits of using FRP components are they are lightweight, corrosion resistant, and easy to install.”
“These are compelling arguments for using this material in future projects, particularly where maintenance access is limited or environmental exposure is high.”
For more information on the full Mt Crosby project, read Seqwater’s fact sheet here – https://www.seqwater.com.au/sites/default/files/2022-04/20042022%20-%20FACT%20SHEET%20-%20New%20Bridge-%20FINAL.pdf
If you have a question about constructing with FRP or want to know if it is a suitable material for a current project, reach out to your local Business Development Manager here – https://www.wagnerscft.com.au/contact-us/
Watch the webinar ‘Constructing with FRP’ to listen to a first-time FRP user talk about his experience with the material – https://www.youtube.com/watch?v=-4AK0EnQIXo&t=6s
Pictured – The completed project walkthrough.
