Walton Bridge – a new arch bridge over the River Thames, UK

Walton Bridge comprises a steel thrust arch with pad foundations supporting a steel–concrete composite ladder deck. The arch ribs have parabolic profile and varying hexagonal cross-section, tapering from springing points to crown, and span 96·1 m. The total rise of the arch is 14·77 m with a span to rise ratio of 6·5. The bridge deck is suspended from the arch by bar-type hangers. Continuous end spans carry the bridge deck between the arch and end abutments, which are full-height reinforced concrete. This paper discusses the method of design employed, including the impact of construction methodology and environmental constraints, together with analysis of aerodynamic effects. It focuses on a number of innovations that were introduced and challenges that were resolved. Two key issues had to be addressed. First, the arch design utilising plastic section properties with reductions to account for the continuously curved steel plating making up the arch ribs. This required local non-linear analysis to demonstrate that the curved arch plating had similar, but slightly reduced, strength and ductility to an equivalent flat plate with the same width and thickness. Hand calculation methods were developed from the results of the analysis. Second, the design and specification of bar-type arch hangers for brittle fracture and fatigue, with insufficient industry guidance on either subject: there is little codified guidance on toughness requirements for bars or on fatigue testing taking angular tolerances at end connections into account, arising both from initial setting-out tolerances and displacements in service from variable actions including temperature effects.