Two existing aluminium under-deck gantries on the Avonmouth bridge were both reaching the end of their operational life. Spencer Bridge Engineering were awarded a contract to undertake a Principal Inspection and any resulting refurbishment work to extend their lifespan. The gantries were required to be lowered to ground level to undertake repairs in a safe and controlled area, removing components from the gantry for off-site refurbishment.
The scope involved a Principal Inspection (PI) to the Design Manual for Roads and Bridges (DMRB) of the two aluminium cantilever gantries on the Avonmouth Bridge. To undertake the inspections, both gantries were lowered to ground level to permit a thorough inspection in a safe working environment. Following the inspection, a detailed PI report was compiled, together with an electrical inspection report, defect register and list of recommendations for remedial works.
Following the PI, remedial works were required, involving weld repairs, full electrical replacement, painting and further assessment work. The assessment work determined the requirement for storm wind bracing, not a feature within the original design. The scope concluded with lifting the gantries back on the runway beams of the bridge and commissioning for handover to the client. A critical aspect of the project was providing assistance to the client with compliance matters and guidance with new design codes since original construction.
The Avonmouth Bridge gantries underwent their first major overhaul since original manufacture. This extensive refurbishment work included a full gantry re-wire, generator refurbishment (incorporating new 316 stainless steel outer casing) and rewiring all onboard emergency stops, proximity sensors, and alarms. Non-destructive testing (NDT) using dye penetration was performed on the structural welds, with any non-compliant welds ground out and re-welded.
The hanger components, including secondary fail-safes and main trolley items, were fully stripped, rewelded as required, straightened, rebuilt, and repainted. All safety critical pins were replaced with new 17/4PH stainless pins, which were bespoke manufactured for the project. A new wind restraint system was designed, manufactured and installed on the gantry, as a result of further assessment work to review fatigue damage since original construction.
Once fully refurbished, the gantries were hoisted back into position on the existing runway beams, re-commissioned and handed over to the client for continued use.
