SSDA 2019: A slender steel Thames crossing

Steelwork’s structural strength made it the only option for a very slender bridge (Image: Anthony Prevost)

Steelwork provided the solution for the latest River Thames bridge, which had to be constructed offsite and erected from a barge due to limited access. 

A new footbridge at Taplow in Buckinghamshire is the latest crossing of England’s second longest river, providing a pedestrian link in the Thames Path and connecting a riverside development with nearby Maidenhead.

Spanning 40m over the River Thames, the shallow arch form of the design is inspired by Brunel’s nearby Maidenhead Bridge and is echoed in the slender steel box structure.

Fabricated triangular-section box girders form the twin structural arches that support the deck, while slender steel hangers complete the composition and ensure the structure is lightweight and transparent in river views.

“The site for the bridge presented numerous access challenges,” explains Clare Taylor, project manager with engineer COWI. “The only viable access route for construction was the river and so it was important to design a bridge that could be constructed easily and safely from the water without compromising the bridge aesthetics within this picturesque setting.”

This challenge was solved by using steel as the primary material, which allowed the bridge to be fabricated offsite in one piece.

Another important consideration was steelwork’s high structural strength and stiffness. It provided the only possible material to realise the architect’s vision of a very slender bridge for this site.

Outward-leaning arches support a composite steel-concrete deck (Image: Anthony Prevost)

The steel structure was designed with structural efficiency in mind but allowing a clear architectural identity. It consists of three key features: the arch, deck and flat plate hangers.

The arches are triangular in cross section and lean outwards to produce a dramatic visual effect, opening up views of the river and landscape.

“The arches support a remarkably slender composite steel-concrete deck formed by a steel tray comprising the edge beams and bottom plate, which was filled with in-situ concrete after the bridge was installed,” says Taylor.

“Transverse stiffeners are revealed below and extend outwards to form the hangers. This composite construction results in improved structural behaviour, particularly from the point of view of dynamic response and acoustics, and it also facilitated easy construction.”

Offsite fabrication by S H Structures was a key factor. It enabled a high-quality finish to be achieved and allowed for a trial assembly, ensuring a more efficient onsite build.

“Installation was the most significant challenge with limited access to the site. This meant a conventional crane could not be used and so the bridge had to be delivered by river,” says S H Structures director Tim Burton.

The structure was transported in three parts by road to a laydown and assembly yard a short distance downstream of the site. The bridge was assembled on temporary works, before the entire steel structure was lifted onto a pontoon, floated upriver and installed using hydraulic jacks in a one-day operation. 

Produced by the BCSA and Steel for Life in association with Construction Manager