Scottish Trunk Road Network - South East Unit - Forth Road Bridge Side Tower Lateral Thrust Bearing

Descriptions

BEAR Scotland is seeking to appoint a suitably experienced SubContractor to undertake the Side Tower Lateral Thrust Bearing Refurbishment scheme with an estimated value 1.2 million GBP.The Forth Road Bridge is a long span suspension bridge which spans over the Firth of Forth linking Edinburgh to Fife. The side Span is 408m long, Main Span is 1006m long.Two longitudinal stiffening trusses form the basis of the suspended structure, which are connected to one another by regular cross girder trusses.At the Side Towers, the ends of the truss transfer vertical load to the side tower through the vertical rocker bearings which sit on top of reinforced concrete corbels protruding from the side towers. Plan bracing is provided between the east and west trusses in the planes of the top and bottom chords, forming bays of approximately 18m (60feet) in length. The plan bracing transfers the lateral loads (primarily wind) to the Side and Main Towers’ lateral thrust bearings.The side tower lateral thrust bearings have not been replaced since the bridge was built. The top laterals taper down and bear onto a milled bearing block. A gusset plate is bolted to the top of the tapering members. The bearing block is in contact with machined cylindrical surface on the bearing slab, forming a vertical rocker bearing.Three 100mm diameter steel tubes are cast in the concrete and through these tubes, 64mm diameter steel bars are post tensioned securing the bearing blocks. The 64mm dia bars have been assessed to be sub-standard and are in need of replacement. The scheme will require at both side towers:- The installation of temporary access provisions to provide access both externally and internally of the reinforced concrete side towers;- The fabrication and installation of a large steel jacking frame.- De-tensioning and removal of three post tensioned bars sequentially at each location followed by the reinstallation and jacking of replacement post tensioned bars.- Installation of a permanent steel bracing bracket which shall be attached to the side tower by coring and post tensioning bars to the existing concrete; and- Amendments to an existing impressed current cathodic protection system.