Saunders Pedestrian and Cycle Bridge

The Saunders Pedestrian and Cycle Bridge demonstrates how advanced steel fabrication, complex plate engineering and digital verification can be combined to deliver a highly architectural structure with demanding structural performance requirements.

The project involved the delivery of a new pedestrian and cycle bridge at Saunders Bridge, Mullingar, providing an active travel link across a highly constrained area involving the Royal Canal, the Dublin to Sligo railway line, existing masonry walls, public footpaths, live services and approach works. While the finished bridge presents as a clean, flowing and visually simple structure, the engineering and fabrication behind it were highly complex.

The bridge is approximately 40 metres long and weighs more than 40 tonnes. It was fabricated in Murphy’s steel workshop in Newbridge and transported to site in two main sections before being installed during a single night operation using a 700 tonne crane. The completed bridge has an architectural curved profile, a weathering steel finish, integrated timber parapets and built in lighting. Each of these features added technical complexity and required close control from design review through to final installation.

One of the most significant engineering features of the bridge is that the steel structure is made entirely from plate. All plates had to be cut, shaped, stiffened, welded and controlled to create the required structural form. This approach was necessary because of the bridge geometry, stiffness requirements and architectural profile. The curved plan, shallow structural depth, variable cross sections and exposed finish meant that standard rolled sections would not have provided the required combination of strength and stiffness. The internal diaphragms, ribs, longitudinal stiffeners and transverse stiffeners were critical. They tied the top plate, soffit plate and edge plates together so that the bridge acted as a stiff, integrated structural section. Extensive full penetration butt welds were required because the plate elements had to work together and transfer load through the full section. Butt welding allowed the plates to behave as continuous structural elements, helping the bridge achieve the required stiffness, strength and durability while maintaining a clean architectural finish.

One of the greatest challenges on the project was maintaining the bridge geometry throughout fabrication. The structure incorporated multiple curves, changing levels, tapered sections, transition pieces and complex interfaces between the deck, parapets, diaphragms, stiffeners and bearing locations. As the bridge was formed almost entirely from fabricated plate, there was little tolerance for error. Any deviation in plate alignment, camber, weld shrinkage or overall geometry had the potential to affect not only the visual appearance of the bridge, but also critical interfaces with the timber parapets, integrated lighting system and site support arrangements. The complex internal arrangement of diaphragms and stiffeners further increased the risk of cumulative dimensional error as fabrication progressed.

To manage this risk, Murphy adopted a combination of traditional fabrication controls and advanced digital verification. Alongside rigorous dimensional checks and controlled welding sequences, the team utilised augmented reality through FabStation to overlay the 3D BIM model directly onto the physical steel structure during manufacture. This allowed fabricators and quality inspectors to compare the fabricated assembly against the design model in real time, verifying geometry, component position and overall alignment before dispatch. Rather than being used as a visualisation tool, augmented reality became an engineering control that supported quality assurance, reduced the potential for rework and gave confidence that the fabricated structure accurately reflected the design intent before installation.

A further challenge was the timber interface. The parapet system was a key architectural feature and included timber posts integrated with weathering steel plates, cleats, rods, bolts, caps and cover details. The timber had to follow the curved profile of the steel structure and connect precisely into the fabricated plates. Steel plates and rods had to be pre welded and coordinated with the timber specialist so the timber elements could be machined, bonded and installed correctly. The detail required close coordination between the steel fabricator, timber supplier and design team, particularly around dowels, slotted plates, countersunk fixings, adhesive bonded rods and removable elements for future maintenance.

The lighting detail added another layer of engineering coordination. The lighting was integrated into the bridge and parapet arrangement rather than added after the structure was complete. Cable routes, ducting, access for pulling cables, luminaire openings and maintenance access all had to be considered during detailing and fabrication. The steelwork had to allow the lighting system to function without compromising the structural performance or the architectural line of the parapet zone.

Installation required the same level of planning. The bridge had to be transported from Newbridge to Mullingar, lifted into a constrained site, positioned over infrastructure and connected accurately to its bearings and supports during a planned rail closure. Temporary propping, lifting arrangements, splice control, CHS pier support and site welded areas all had to be managed so the final geometry matched the design.

The true achievement of this project lies not in what is visible, but in the engineering hidden within the structure. More than 5,500 fabrication hours were invested in transforming thousands of individual plate components, diaphragms, stiffeners and full penetration butt welds into a single, continuous structural system. What appears to be a simple architectural bridge is, in reality, a highly engineered plate structure where structural performance, fabrication precision and visual quality had to be achieved simultaneously. That level of complexity, executed successfully and largely unseen, is what makes this project exceptional.