Award winning deck repairs to the M20 Chatham Road bridges in Kent represent the use of innovative techniques while having minimal effect on the natural and built environment and resulting in substantial savings on the overall project cost.
The project, undertaken by InterRoute, our highway management joint venture with Balfour Beatty Infrastructure Services, provided a novel engineering solution to the task of in-situ repair and restoration of the damaged steel beams of the motorway bridge decks at a congested traffic location with minimum disruption to the road users. Normal repair would have involved cutting out damaged sections of the distorted beams, replacing them with new sections and installing new bracings – a process that would have cost £800 000 and required temporary propping of the steel beams during site repairs. This would have resulted in complete closure of the north bound carriageway of the A229 and the coast bound carriageway of the M20 at junction 6, which is already known as a traffic congestion hotspot during peak hours. To overcome this the damaged sections of the beams were repaired, instead of being replaced, using ‘heat straightening’. As a result all the repair works were done during off-peak night time road closure of the north bound A229 and lane closures on the coast bound M20.
Heat straightening is an innovative technique developed and widely used in the USA. Its application in the UK has been limited but as the method is enhanced it’s becoming more accepted. The process involves heating the bent sections of damaged beams to around 600ºC using a heating torch following precisely defined patterns. As the heated sections cool and shrink, a combination of restraint from the surrounding cold parts and external jacking forces bring the beams back to their original shape. The heat straightening repair of the M20 Chatham Road bridges won industry recognition in the innovation category of the Thomas Brassey Awards given by the Institution of Civil Engineers Kent and East Sussex Branch.