Spencer Bridge Engineering were awarded the contract by Transport Scotland to deliver four new permanent access gantries under the East and West cantilevered footways on the Erskine Bridge. The package of works included a full turn-key solution to design, construct, install and continually maintain the gantries to support the clients year-round inspection activities of the structure.
The new gantries were required to be designed, manufactured, factory acceptance tested and installed on the bridge to meet the requirements of the project specification, runway beam loading constraints and the IStructE Purple Book.
A number of constraints were placed on the gantry design by the client, including to be lightweight in their construction and achieve sufficient traction on the existing runway beams. In addition, the gantries were required to dock at dedicated points on the bridge to align with access gates in the tall pedestrian parapets.
The full gantry system was to be controlled via a HMI panel on board of the gantry, allowing users to interact with the traversing operation and control gantry functions and outputs. The construction was to be tested prior to installation, to ensure the as-built gantry performed in accordance with the design specification and client requirements.
In addition to the design requirements, training and ongoing maintenance was to be provided, to ensure the gantry was operated and maintained, to prolong its safe operational use.
An innovative lightweight aluminium gantry was designed specifically to suit the bespoke requirements of the Erskine Bridge geometry and constraints. Traction was achieved by designing a specialist drive system that reacted wheels perpendicular to the runway beam webs, mitigating potential issues and premature wear associated with complex interactions between the main load bearing wheels.
The gantries were profiled to allow passage through the existing deck web access platforms, whilst ensuring adequate clearances were achieved. For passage over the expansion joints, a load transfer arrangement was developed that can be deployed when reaching this area.
The electrical control system was configured to monitor position on the bridge and correct for skew position due to bridge geometry.
Each gantry was built off-site and factory acceptance tested to the designers requirements. Once installed on the bridge, the gantries were put through site acceptance testing and commissioning to ensure acceptable performance and interaction between the runway beams. Once handed over, the clients representatives were trained in various operational roles to ensure compliance with the IStructE Purple Book. Following the project, an ongoing maintenance and support contract was awarded to Spencer Bridge Engineering to ensure the gantry was kept in optimum working order to maximise its lifespan.
