EXTRA STEELWORK is needed to strengthen the troubled Thelwall viaduct, adding £10M to the £42M already being spent to renew worn bearings, the Highways Agency has revealed.
Latest investigations have confirmed that the 40 year old structure will require stiffeners to be added to its riveted steel plate girders and crossbeam members to beef them up while the bearings are replaced.
The 1.4km long viaduct carries the M6 motorway over the Manchester Ship Canal and River Mersey near Warrington.
Routine inspection of the structure in 2002 revealed that some bearings had failed but by July 2003 the Agency decided to replace all 150 bearings at a cost of £42M (NCE 3 April 2003).
'The Highways Agency wanted to ensure that on completion of the bearing work the viaduct had a sustainable future, ' said Highways Agency project team leader David Brindle.
'Horizontal stiffeners are being placed to prevent the [existing] vertical stiffeners and beams themselves buckling, ' he explained. 'When the bridge was designed in the 1960s, it was for totally different traffic loads to today.'
The structure was refurbished in 1996 to replace the existing deck and expansion joints which had suffered corrosion from de-icing salts. The number of joints reduced from 37 to four.