A DAMAGED steel bridge beam spanning the M5 near Weston-super-Mare in Somerset is being straightened using a revolutionary heat treatment technique.
Originally developed in the US, the technique is being trialled by the Highways Agency on the 25-year old New Road overbridge near Junction 22 on the M5.
The bridge was struck by a tipper truck early last year. The accident caused the outer 840mm x 290mm Universal Beam to displace by 400mm over a 2.5m length.
To repair the beam, oxyacetylene torches are being used to heat the lower flange to between 500 and 600degreesC in a V-shaped pattern. Horizontal jacks restrain expansion away from the original line so that, as the beam cools, internal stresses develop and gradually straighten it.
According to the Agency, conventional repairs would have required one carriageway of both the busy motorway and of the overbridge to be shut for up to seven weeks while the damaged section was cut out and replaced.
The cost of this alternative was estimated at more than £250,000.
However, specialist subcontractor Fairfield Mabey is hoping to complete all remedial works within seven days at a cost of about £150,000.
US research is said to have shown that, provided local steel temperatures never exceed 750degreesC, the strength of the straightened beam is virtually identical to its original value.
For full report, see NCE Road supplement 22 June.