The existing underdeck gantries on Tay Road Bridge are both reaching the end of their operational life and are frequently unavailable due to breakdowns. Spencer Bridge Engineering were awarded two contracts to apply their specialist knowledge and experience to the design for replacements. The bridge operator required several options looking at, including refurbishment of the existing gantries, like-for-like replacement, similar-to-existing replacement with upgraded and modernised features, or a more radical departure from the existing design.
The first contract considered the options available, including practicality, programme and cost. The original gantries were first brought in to service in 1986 and a study of historic and applicable up- to-date standards was needed to inform the final chosen design route. The bridge board also desired to improve access and welfare, both for health & safety reasons and to be more operationally efficient.
The second contract took the chosen design route and developed it to a stage where the documents provided would form the basis of a Design and Construct Tender for the client to issue to selected contractors.
The resulting design-and-tender package included Approval in Principle (AiP) documents for the structural, mechanical and electrical designs, a report outlining the constraints of the existing runway beams, a Safety Consultation document, a User Requirement Specification, an Operational and Maintenance Guide and a summary of the unusual risks associated with bridge gantries in general and more specifically with Tay Road Bridge.
Following on from completion of the first contract, Spencer Bridge Engineering were instructed to further develop the replacement gantry design based on a similar-to-existing form that complied with current standards and codes and also provided improved access, shelter and welfare facilities. Of fundamental importance to any gantry design is to consider the safety and working conditions for the end users.
With this information, Spencer Bridge Engineering’s in-house design team developed the design specification to incorporate many of the desired improvement aspects highlighted by the operatives, supervisors and managers.
The revised specification incorporated a range of improvements to enhance safety, access and long-term usability. These included better load distribution from the trolley wheels, improved clearances at known pinch points, more efficient staircase access in place of ladders and easier access for the inspection, maintenance and replacement of mechanical components.
The client also sought to future-proof the gantries by enabling a transition to rechargeable battery power, introducing an incinerating toilet and kitchen/mess room to support longer periods on board, providing additional control stations, creating a dedicated refuelling and service area and improving handrail containment to remove the need for a safety boat to remain on standby.
