Steel special: Sustainable steel delivers Worcester’s new bridge
The bridge sections fabricated by Cleveland Bridge in S460K2W+M steel, ready for transport to Worcester
Cleveland Bridge delivers a UK first with use of new steel on construction of River Severn crossing.
An innovative new steel composition has been employed in Britain for the first time on a new river crossing in Worcestershire, which is intended to be a more sustainable and cost-effective bridge structure.
Steelwork contractor Cleveland Bridge UK is constructing the new Carrington Bridge in Worcester from S460K2W+M, a higher-strength, fine-grained structural steel with improved atmospheric corrosion resistance, which has been used on structures in North and South America, France and Turkey.
“Due to its chemical composition, this steel develops a patina with increased resistance against atmospheric corrosion in comparison with standard structural steels,” explains Phil Bailey, chief technology officer at Cleveland Bridge UK.
“The thermomechanical rolling process in its manufacture allows fewer alloying elements, leading to a lower carbon equivalent value (CEV), which offers an improved weldability compared to normalised weathering steels of the same strength. The steel can therefore be used in steel constructions for bridges and high-rise buildings where a higher-strength weathering steel with good weldability is required.”
CGI of the road improvement scheme, showing the new bridge
The new bridge is part of Worcester-shire County Council’s project to dual the A4440 Southern Link Road and will sit alongside the existing Carrington Bridge crossing the River Severn. Main contractor Alun Griffiths was appointed to deliver the improvement scheme.
The crossing was originally planned to mimic the design of the existing six-span bridge. “Using S460K2W+M enabled the new bridge to become a more economic three-span structure,” says Bailey.
The revised design, produced by a Burroughs/COWI Design joint venture, working with Cleveland Bridge UK, reduced the number of piers from five to two, which delivered savings as a result of decreased material requirements.
Fabricated at Cleveland Bridge’s facility in County Durham, the 873 tonne bridge was produced in four lines of girders to form two braced pairs. The main girders, diaphragms and stiffeners were produced from S460K2W+M with channels, bracings, cross girders and splice plates using another weather-resistant steel (S355J2W+N).
Work on the steel sections in Cleveland Bridge UK’s facility
“The new steel decreased the plate thicknesses, which therefore reduced its weight by around 15% to 20%, due to its higher minimum yield strength of 460 MPa – an approximate 30% increase against S355 steel,” says Bailey.
“It also reduced the workmanship, as the thinner plates required smaller welds and the possible need for doubler plates. The steel has improved weldability due to its reduced CEV of typically 0.47, which combined with thinner plates required a lower pre-heat process.”
S460K2W+M steel is based on a product named DIWETEN 460, produced by a German mill, Dillinger.
Cleveland Bridge’s use of the steel on the Carrington Bridge has been CE marked in accordance with BS EN 1090-2.
After a trial assembly, the sections were transported by road to site. They were delivered as four lengths of braced pairs and two lengths as single girders then assembled into six braced pairs using two 500-tonne crawler cranes.
“S460K2W+M offers production, operational and cost efficiencies, which is a benefit to all parties involved in major structural steel projects,” says Bailey.
The new bridge is scheduled for completion in spring 2020.