Contemporary solution for a traditional bridge
In 2004, work started on the construction of a new inner relief road in Sheffield. The construction of a new 1.5km dual carriageway was duo to take approximately two years and was required to ease traffic congestion in the city and help regenerate parts of the city after years of decline.
The area is well known for its Victorian rail bridge and the new proposed structure, built in the Wicker Arches, had to complement this. As well as having the appearance of a traditional steel structure, it also had to have concrete parapets for containment of any accident on the line. Birse was the chosen contractor to deliver the new road and CEMEX was appointed to construct the new bridge.
It was agreed that the bridge should be constructed of 40 precast concrete parapets with steel plates cast into the units. When painted, this gave the structure a traditional appearance without incurring any additional cost. To complete the appearance, large stainless steel angles were developed to allow for fixing. In addition, new copings
were required along the wing walls to the new bridge and these were precast using coloured concrete to match existing units.
Working with Birse, the design for the components of the bridge evolved to ensure various criteria were met. In order to withstand adverse weather, the steel plates at the rear of the parapets had to be galvanised and painted. When galvanised, the units were prone to warp, so stiffening plates were added that also allowed for fixing. As the plates were larger than the parapets, this presented problems in casting the units. It was decided to cast upside down in wooden moulds, using the galvanised steel plate for one side of the mould.
In order to fix the units, a stainless steel angle was required to be cast into the toe. Over time the design was developed and a non-standard angle made from Duplexgrade stainless steel resulted, which would hold the units in position in the event of accidental impact.
The following were used in the construction, including 172 tonnes of precast concrete for the parapets and copings: Parapets
2 × 2300mm
36 × 2110mm
2 × 1540mm
120 tonnes of C40/50 strength class, grey self-compacting concrete.
17 × 1450mm
1 × 920mm
30 tonnes of C40/50 strength class, grey self-compacting concrete.
These were made from hot-dipped galvanised steel painted to the client’s specifications.
These were made from Duplex-grade stainless steel.
Standard high-tensile steel was used for all units.
CEMEX delivered the units to site, with the steel plates pre-painted, to coincide with Birse’s construction programme. To keep disruption to the railway line to a minimum, the line was slewed away and the first 20 parapets and 16 copings were delivered and installed in January 2006. The track was then moved back to its original position and the construction of the bridge continued. The remaining parapets and copings were delivered in July 2006 for the other side of the bridge. CEMEX also supplied ten profiled coping units for the abutment walls, which were designed to match existing stonework.
In order to achieve the appearance desired by the client for this new rail bridge, the construction approach adopted by the developers had to consider the twin challenges of traditional design and modem reinforcement.
IAN TUPLING, CEMEX
Copyright The Concrete Society Mar 2007
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