Due to the harsh marine environment of the Forth Road Bridge (FRB) location and their age, the existing underdeck access gantries on the Forth Road Bridge had reached the end of their operational life and a more refined and robust version was required. Spencer Bridge Engineering were awarded the contract by Amey and Transport Scotland to build; CE Mark and off-site factory acceptance test a new high specification main-span under-deck motorised gantry.
The new gantry was required to be manufactured, painted and off-site factory acceptance tested to meet the stringent criteria of BS EN 1090-2 Execution Class 3 (EXC3), specification for highway works and the IStructE Purple Book.
Particularly robust quality control procedures were in place for the duration of the works to ensure the gantry met the design life required and withstood the environmental conditions the gantry would be exposed to within the location of the Forth Road Bridge.
In addition to the gantry primary structure, two bespoke MEWP’s were also manufactured to EXC3 and mounted to the frame, which provide access to the under- deck of the FRB when in service.
The gantry control system was required to be modified to include additional equipment over and above the previous gantry design, and integrated as required into a previous EC&I design of the new gantry. The new gantry was mounted onto a dedicated test rig and subjected to a number of mechanical and operational tests to verify performance against the designers requirements.
Despite the project running through the full period of the Covid-19 restrictions, mitigation was put in place to minimise the impact to programme and budget.
Robust systems of inspections on the steel-work and painting were implemented throughout the project and reported back to the client to demonstrate compliance with the specification and designers requirements.
Minor improvements to the design were made during the construction stage in collaboration with the designer, to ensure a very high specification gantry was provided to the client, maximising operational lifespan of the equipment for years to come.
