It had a good run. But after more than 200 years of service spanning the River Tweed between England and Scotland, the one-lane Union Chain Bridge wasn’t meeting modern mobility demands. So in July 2020, the Northumberland County Council hired U.K. engineering firm The Spencer Group for a £7.1 million project to repair the storied landmark.
“It’s the bridge both physically and metaphorically between Scotland and England,” says Neil Hewitt, project director, Spencer Group, Goxhill, U.K. “It's massively important, not only to the engineering world, I’d say, but also the two communities that it serves.”
The goal wasn’t just to preserve the world’s oldest suspension bridge still carrying traffic but also to improve the flow of vehicles. With a weight limit of 2 metric tons, the 137-meter (449-foot) structure had been forcing drivers with heavier loads to take a 19.3-kilometer (12-mile) detour.
To preserve every possible original piece, team members first had to meticulously deconstruct the bridge. Over the span of 18 months, they examined the condition of more than 10,000 suspension components to determine what could be repaired and what needed to be replaced—carefully tagging each piece so it could be reassembled in its original place.
The project involved dismantling and refurbishing the bridge, which proved to be a daunting chore. The team removed the timber deck, 800 cast iron chain pins, 146 wrought iron hangers and thousands of nuts and bolts. It also took apart 444 chain rods that weighed a combined 33 metric tons. Project leaders established an onsite facility where the team could clean, restore and repaint original items—but they also made a painful discovery.
“Only when we dismantled the bridge and removed all of the old parts, stripped the paint and assessed them did we see the reality,” says Hewitt.
While the team was able to preserve about 30 percent of the original suspension chains, the rest had to be replaced with new ones designed to be identical to the originals. The pins that fasten links and chains fared better, with the team able to reuse the majority of the originals.
Project leaders also found an innovative way to meet archeological and ecological protection constraints—while also keeping workers safe as they installed bridge cables high above the rapid-flowing river to support their access system. By working with French engineering company VLM, the team was able to install a platform and two cradles from which they could access all parts of the suspension structure, without disrupting the water or surrounding land. The system also included a crane that carried heavy elements of the bridge across the river.
Along the way, the team also built in opportunities for local economic development. It used a local masonry company for the project’s stone work, and sourced all new stone from the same local quarry that produced the bridge’s original materials in 1820.
The project team engaged with local stakeholders in other ways, too. For example, the team upcycled old timber beams and steel from the bridge to build a commemorative bar in a nearby village and handed out bags of timber to community members for firewood. The Friends of the Union Chain Bridge consistently praised the team’s work, which Hewitt noted was quite a coup.
The final piece in keeping community stakeholders happy? Reopening the bridge, which is slated to happen in quarter three.