The existing underdeck access gantries on the Kessock Bridge had reached the end of their operational life, meaning a more refined and robust version was required. Spencer Bridge Engineering were awarded the contract by BEAR Scotland and Transport Scotland to fully design, build, install and commission a new under-deck motorised gantry that could be used year-round to maintain the bridge for the client. The new access solution would need to allow access to the entirety of the under-deck area and outer faces of the main girders, as well as providing a solution for emergency escape from the gantry in all locations on the bridge.
The new gantry was required to articulate around the geometry of the bridge in order to run freely along each span, providing access to the under-deck of the bridge as well as the piers and the exterior of the bridge utilising specially designed scissor lifts on each end of the gantry.
The scope included upgrades to the gantry parking area at the North side of the bridge to allow the gantry to be safely stored and maintained when not in use. The gantry could be jacked up from the bridge utilising specifically designed jacking frames, permitting a detailed inspection of the load bearing components of the gantry, prolonging its operational lifespan, and maximising its availability.
In addition, improvements to the gantry infrastructure were installed in the form of dedicated gantry charging points along the length of the bridge at selected piers, to ensure the gantry can be plugged into electrical supply when not in use, ensuring optimum maintenance and prolonging its operational life.
The gantry is one of the most complex designs of this type of equipment known, which demonstrates Spencer Bridge Engineering’s competency in multi-disciplinary engineering, by combining mechanical, structural and electrical expertise.
Spencer Bridge Engineering’s in-house mechanical design team designed the gantry from concept to detailed design. An innovative design feature of the gantry includes hydraulic ‘span compensator’ cylinders (rams) which the full weight of the gantry structure is suspended from. Each of the rams is connected to a piston accumulator system, which provides a constant force onto the rams to assist with skew control and anti-crabbing when traversing along the runway rails. Full information and feedback is provided through the HMI control screen, providing the operator with complete control of the gantry functions.
The gantry was factory acceptance tested, site acceptance tested, commissioned and handed over to the client by Spencer’s in-house bridges delivery team.
