Ralph's Bridge Investigation and Replacement Design
Sterling investigated tree-impact damage to the 58-metre Ralph's Bridge in Cobboboonee National Park and designed an AS 5100-compliant steel replacement for six spans, configured for helicopter delivery and a 100-year design life.
Challenge
A fallen tree damaged six spans of the 58-metre timber pedestrian bridge on the Great South West Walk. Following an earlier visual inspection, the land manager needed a detailed investigation to determine whether affected elements could be rehabilitated or required replacement. Any replacement also had to meet current AS 5100 requirements and be practical to construct in a remote location accessible only by helicopter.
Solution
Sterling inspected the affected spans, measured pile inclinations and undertook timber boring at excavated pile locations to assess below-ground condition. Although selected piles remained in fair condition, the combined damage and loss of structural continuity meant repair alone could not reliably meet current loading and safety requirements. Sterling completed an options assessment and developed a steel-girder replacement for Spans 1 to 6, supported on reinforced concrete pad footings and configured as segmental, simply supported components suitable for helicopter delivery. The design was progressed through Issued for Review and Issued for Construction stages for a 100-year design life.
Deliverables
Deliverables comprised an engineering investigation report covering the affected spans and pier groups, an options assessment and Issued for Review and Issued for Construction design packages. The design package included structural drawings, a Safety in Design register and geotechnical assessment for the replacement structure.
Outcome
The investigation confirmed that the cumulative damage could not be resolved through repair alone. The replacement design provided a durable, AS 5100-compliant crossing with a 100-year design life. Its segmental, simply supported arrangement improves maintainability by allowing an affected section to be replaced independently following any future tree impact, subject to engineering assessment.
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