The 1km long cable-stayed Kessock Bridge crosses the Beauly Firth at Inverness in Scotland and its existing gantry required replacement, as it had come to the end of its structural design life, having been installed 35 years ago, two years after the bridge opened in 1982.
The 24-tonne gantry follows the complex geometry of the bridge while the platform holding the operators remains level and has a scissor lift at each end of the platform to allow operators easy access for maintenance and inspection of the bridge overhead.
Our project team has applied high-level ingenuity and innovation throughout the project and the bespoke gantry is currently being installed in two phases.
We are delivering the challenging project for BEAR Scotland, a service provider in the Scottish roads maintenance sector, on behalf of the national transport agency for Scotland, Transport Scotland.
Andy Beach, Operations Director said: “Our depth of in-house knowledge and expertise has allowed our team to design and build the new under-deck access gantry before carrying out the complex process of installing it on the bridge following extensive off-site testing.
“Our innovative solution will allow access to the entirety of the under-deck area and eliminate the need for scaffolding, reducing costs and limiting the impact on the normal operations of the bridge.
“This has been a hugely complex and technically challenging engineering project. We are proud that we have been able to provide such an innovative and effective solution for the client.”
The gantry, which is 21 metres long and six metres wide, will operate 29 metres above the water and is able to travel the full length of the bridge. The project also involves a detailed survey, inspection, refurbishment and repair of the existing gantry rails underneath the bridge deck that the gantry will move along.
As part of the project, the gantry parking area at the north side of the bridge has been upgraded to allow the gantry to be safely stored and maintained when it is not in use.
In addition, improvements to the gantry infrastructure have been installed in the form of dedicated charging points along the length of the bridge at selected piers, ensuring the gantry can be plugged into an electrical supply when not in use, ensuring optimum maintenance and prolonging its operational life.
Luke Fisher, Off-Site Project Manager for the scheme, said: “We believe this is one of the most complex mobile access gantries developed for any structure anywhere in the UK and it is completely bespoke to this bridge.
“It demonstrates Spencer Group’s capability in multi-disciplinary engineering by combining mechanical, structural and electrical expertise. Bringing all of these elements together is where the true innovation comes in.
“Due to geometry and curvature of the bridge, the gantry must self-level in two planes to allow the platform to remain level for the operators. The control system has an array of sensors installed on the gantry, which respond to geometry change in the bridge structure and allow the gantry to safely negotiate along its full 1km length of travel.
“The gantry is supported by hydraulic rams on each corner, suspending the full weight of the 24-tonne structure. Through the control system, they extend and retract to the position of the existing gantry rails, which vary by 160mm, essentially allowing the gantry to grow in length.”
We hold an exceptional track record of successful specialist bridge schemes, including being appointed to carry out a long-term maintenance painting programme on Scotland’s Erskine Bridge. The bridge spans the River Clyde near Glasgow and the £18m package of works is being carried out over a four-year period on behalf of Transport Scotland in the most extensive maintenance painting of the landmark crossing for a generation.
Earlier this year we completed a £10m project to complete repair works which followed a fracture that caused the closure of the Forth Road Bridge near Edinburgh. That scheme involved the replacement of the truss end links, which connect the bridge deck to the towers, with a unique new sliding bearing system designed by Transport Scotland’s consultants Fairhurst.
Find out more about our expertise in bridge maintenance HERE