The Mandurah Road Footbridge crosses Mandurah Road and the PTA rail lines in Mandurah – to provide direct access to the Mandurah Rail Station from a nearby education campus. The bridge consists of two fabricated steel box girders that taper towards the crown of the arches. The structural steelwork is finished with a three coat Polysiloxane coating system that is required for both corrosion protection and appearance.

BG&E were requested to develop a methodology to investigate the condition of the coatings, defects and coating failures, and confirm if the defects are related to the coating application, exposure, or lack of maintenance.

The inspection methodology included

• The use of drones and other camera technologies for visual inspection of inaccessible areas.
• Identification of sampling locations, destructive and non-destructive testing, and sample requirements for laboratory testing.
• Testing requirements for coating adhesion, total dry film thicknesses and thicknesses of individual coats, assessment of surface preparation and analysis of coatings (laboratory methods).
• Consideration of access issues related to working over a busy four lane divided road and rail corridor, weight limits for access equipment on the footbridge and pedestrian traffic.

In addition to the inspection methodology, BG&E developed a coating specification suitable for undertaking site repairs to the protective coatings on the footbridge.

The specification took into consideration

• The existing coatings condition and compatibility with repair coats.
• Surface preparation methods suitable for site works.
• Specification of coatings compatible with the existing coatings, suitability for site application in limited time windows available, and a service life comparable to that of the existing coating systems.
• Maintaining the appearance of the bridge.