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New Bridge beams and concrete deck slabs for Birse Rail’s Piano Overbridge24th April, 2012 by Gillian Murtagh
Working with Steve and the Birse Rail Team an initial value engineering exercise was carried out by the Shay Murtagh Design Team and a substantial reduction in the number of prestressing strands required in the box beams was proposed. Shay Murtagh was subsequently granted detailed design responsibility for the bridge beams, deck slab, parapet upstands and bearing schedule. On design completion a Design Check was completed by consultants Roughan & O’Donovan wherein the reduction in prestressing strands was verified along with the full detailed design for the structural components mentioned above.
The project consisted of 26 no. 700mm deep x 750mm wide prestressed box beams used within two simply supported spans. 13 no. beams were 19.875m long and 13 no. beams were 18.95m long. The beams were tapered at the ends to a minimum depth of 600mm in order to accommodate the road profile. A portion of the parapet upstands was batched with the edge beams to minimize formwork and eliminate falsework on site. The edge beam and parapet upstand batched assemblies weighed a maximum of 36.5t while the individual box beams weighed a maximum of 24t.
6 no. cill beams installed on the existing abutments and 3 no. cill beams installed on the existing pier were also manufactured as part of this contract. The cill beams varied in weight from 9.7t to 20.2t.
The bridge has a skew angle of 3.7° and the completed deck had a clear width between parapets of 9.1m and spans between centre lines of bearings of 19.466m and 18.4m.
A trial erection was completed in house and an inspection team from Birse Rail and Network Rail attended. Logistics worked closely with the on-site team and installation began on 2nd March under a strict rail possession.
“This was a challenging project but it showcases our design strength as we want to give our project partners the best possible solution both economically and structurally” – Steve Lowe Senior Design Engineer. It was a pleasure to work with Steve Harper and the Birse Rail Team and we look forward to our next project together.