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The Wellington Bridge is a three span overbridge constructed in 1965 of steel concrete composite construction which includes a cantilever and suspended span arrangement. The bridge carries a single carriageway over the A12 Hatfield Peverel Bypass trunk Road. There are 7 No girders with half joint detail which supports the deck spanning approximately 27m overall between the East and West piers.
The structure was initially struck on the cantilever span of Beam 7 on the 23rd February 2010 and again for a second time on 21st May 2012 with a vehicle striking the bottom flange of the suspended span steel beam around 0.55m from the half joint. In addition Beam 6 and beam 5 had sustained impact damage.
HS Carlsteel were contracted by Interserve to undertake heat straightening of the damaged girders. The option of full beam replacement was not considered viable, however sections of one of the Girders was not salvageable and it was necessary to undertake a partial replacement with larger sections receiving a heat treatment to reinstate them to acceptable limits. HS Carlsteel employed the services of Corodus Consultants Ltd to assist with the development of the heat plans and methodology and oversee the operation
Works included:
A detailed heat plan will be produced prior to commencing the heat straightening operations
Global Sequence of Repair Works
Agree general methodology
Undertake trials (if deemed necessary)
Shot-blast\Remove paintwork to affected areas.
Mobilise and Set up Datums on beam.
Remove Stiffeners\Determine Elastic Recovery.
Out of Plane Deformation Survey, MPI & hardness survey
Locate Yield Line, Heat Plan, Straighten beam (s) MPI and hardness survey
Final Out of Plane deformation survey
Heat straightening is generally applied to areas that have either experienced yield or are immediately adjacent to areas that have experienced yield. It is not applied to otherwise undamaged areas of plate. None of the previous surveys had identified yield zones, and in particular the extent and location of plastic hinges. This was necessary to establish the final heating plans. The first item in the procedure was to establish if any permanent plan deformation of the flanges of either girders 6 or 7 existed. If so “S” classification repairs, as per the FHWA Manual, requiring intermittent Vee-heats and general access throughout the span would be necessary.
The procedure called for a survey at 1m centres throughout the suspended span. However, access was not available to do this and the straightness of the flanges was assessed visually from the working platform around the impact points. It was agreed by all parties that no plan curvature was evident to the bottom flanges of girders 6 and 7 prior to the commencement of heat straightening operations. Plastic hinges were identified below the top flanges of both girders 6 & 7. On girder 7 the plastic hinge extended from Ch300 to Ch2900. The tangent point A could not be directly identified but was judged to be close to the flange/web root radius. Tangent point B was 50mm below the top flange at Ch300, and 80mm below the top flange at Ch3000. No plastic hinges were found below half joint level.