Structural Steel Design Awards 2021 - Merit

These steel truss bridges over the Greta River in the Lake District at two sites, Brundholme and Low Pearson, form part of the reconstruction of the Railway Trail connecting Keswick to Threlkeld following the winter flooding of 2015.

Access to the bridge sites for construction plant and a mobile crane was problematic. The bridges were to be built ‘in-line’, the Brundholme site had to be crossed in order to access the Low Pearson site, and it was uneconomic to design the permanent structure at Brundholme to support the construction traffic loading. In addition, any works in the river carried a number of risks to the environment, programme, safety and cost as the area was subject to flooding.

The solution was based on using a modular temporary steel bridge, adapted to fit on the permanent foundations at the Brundholme site, but designed to accommodate 44-tonne construction traffic. This temporary bridge, which was launched into position, gave the construction team access to the Low Pearson site and facilitated construction of the paths and roadway to the second site, as well as the bridge itself.

The Low Pearson bridge was fabricated in three sections, delivered to a compound adjacent to the Brundholme temporary bridge, loaded on temporary vehicle bogies and moved to site by tractor. Once onsite, the sections were bolted together, fitted with a unique temporary launch nose adapter, temporary launch frame and lower boom launch runway beams, which enabled the bridge to be launched into final position without damaging the permanent works. Once the bridge was in its final position, the launch rollers, launch nose adapter, launch frame and lower boom runway beams were all removed.

The same innovative system was used for the Brundholme Bridge, with the permanent structure being assembled on the far bank of the temporary bridge. Again, this structure was fitted with the same temporary lower boom runway beams and frame as at Low Pearson, but was spliced to the end of the Brundholme temporary bridge. This enabled the same launching operation to both launch the new permanent bridge, and de-launch the temporary access bridge, improving programme and eliminating further risk. Once the permanent bridge was in its final position, the temporary launch frame and lower boom runway beams were removed and recovered for recycling. The steel temporary bridge, launch nose and rollers were all returned to the supplier to be reused on other projects.

Architect

Capita

Structural Engineer

Beaver Bridges Ltd

Steelwork Contractor

Jamestown Manufacturing Ltd

Main Contractor

Cubby Construction Ltd

Client

Lake District National Park Authority

Judges' comment

These new bridges replace ones that were washed away during storm Desmond in 2015. The team cleverly adapted existing erection techniques to address the inaccessibility of the two sites, reducing the installation cost and minimising any detrimental impact on the surrounding area which is inside the Lake District National Park.