Connel Bridge Walkway merges safety, innovation, and a heritage structure

Heritage bridge works specialist The Spencer Group completed a complex and unique walkway on Connel Bridge. The Grade B-listed structure links the villages of Connel and North Connel, near Oban Scotland; spanning Loch Etive. The project involved designing, constructing and installing a 240-metre-long walkway along the full length of the bridge. The project began in January 2022 and was completed for BEAR Scotland, a service provider in the Scottish roads maintenance sector, on behalf of Transport Scotland. The new walkway has a design life of 50 years and is cantilevered off the east side of the bridge. The 2-metre-wide walkway extends out up to 4.5-metres around the tower legs, negotiating the complex shape of the structure and allowing pedestrian access throughout planned works to replace the entire deck over the coming years

Extending the existing structure

Corrosive maritime environment

Zero Maintenance

Specialist pointcloud survey and precision mapping

The design of the walkway employed the use of the latest design technologies to analyse the walkway structure, assessing the effects of various load conditions to provide an optimised and safe design. The design is unique by the way it interfaces with the existing bridge structure. A non-invasive clamping solution was developed to accommodate the rivets present on the bridge chord relative to the primary walkway beams. To maximise the efficiency of the walkway install, the use of a pointcloud survey enabled the accurate positioning of members and therefore minimised the risk of on-site clashes. This also provided the precise mapping of the transition from the existing path to the new walkway. This reduced the modifications to the existing masonry structure in order to respect the heritage of the bridge.

best structural design practice

Complexity of design but ease of construction

The walkway structure is constructed from over a thousand components, each individually hot dip galvanized to a thickness of 85µm. This process was chosen not only for its functional benefits but also for its aesthetic harmony with the existing structure. Despite the painted structure of the bridge, the chosen galvanized finish with a weathered patina seamlessly blends in with the surrounding steel, ensuring a visually cohesive integration.

The decision to opt for galvanizing, over other methods of protection, took into account both practical considerations and long-term durability. Recognizing the logistical challenges posed by the bridge’s constraints, galvanizing emerged as the optimal solution, facilitating seamless installation while offering a robust finish capable of withstanding the rigors of site location.

Cost-efficiency of galvanised steel

Uncompromised safety, affordable, long-term durability

A comprehensive cost analysis underscored the superiority of galvanized steel over traditional painted alternatives, particularly in terms of both time and expense associated with future maintenance and repairs. This strategic foresight ensures not only immediate efficiency during installation but also long-term cost-effectiveness, aligning with the project’s overarching objectives. Given the bridge’s exposure to harsh environmental elements, corrosion resistance emerged as a paramount concern. With an anticipated corrosion rate of 1.5µm per year, the specified finished coating thickness of 85µm promises an impressive life of 57 years, surpassing the design life expectancy of the walkway itself. This judicious selection not only ensures structural integrity but also minimizes the need for costly and disruptive maintenance interventions, thus safeguarding the longevity and functionality of the infrastructure for generations to come

Galvanized walkways and bridges

Specifying Hot Dip Galvanising for bridges and walkways

For the vast majority of applications, hot dip galvanizing can be simply specified using the following reference: Hot dip galvanized to EN ISO 1461 : 2022 by a member of Galvanizers Association.

This standard contains coating thickness requirements which will typically be sufficient to achieve a long coating life for all environments.

For instances where an increased coating thickness is required to achieve a longer coating life, or where work will be exposed in a severe service environment, steelwork may be grit blasted prior to galvanizing. This produces a coarse profile so opening up more steel surface to react with the molten zinc resulting in a thicker galvanized coating.

We have extensive technical information on how to specify for hot dip galvanizing.

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