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The A14 Huntingdon Viaduct is a post-tensioned concrete box bridge built in the mid-1970s. It carries the busy A14 dual carriageway across the Brampton Road overbridge and the East Coast Main Line (ECML). Strengthening work called for beams to be placed under the viaduct to reinforce and support the half joints carrying the midspan over the railway lines and Brampton Road.
The viaduct has six spans, the third and fifth being post-tensioned reinforced concrete sections that cantilever over piers into the fourth span. It is here that half joints support the main precast beams crossing the Brampton Road overbridge and the ECML.
Following growing concerns over the strength of the viaduct, three major defects were identified as requiring urgent remedial work. Concrete was spalling at the top of the piers, exposing the reinforcement. The main half-- joints were judged to be under strength due to a lack of reinforcement, and the post-tensioning tendons in spans three and five were regarded as insufficiently grouted.
A major part of the strengthening work involved bolting a series of steel beams to the underside of the cantilevered sections to support each precast beam, relieving the load on the suspect half-joints. These beams were 8-14m long and weighed 5.5-8.7 tonnes.
Additionally, as...