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Brick parapets are no match for 24t trucks

Engineers are divided on whether it is practical to strengthen the UK’s bridge stock to avoid accidents similar to the Oxshott crash.

Bill Harvey, a specialist consultant on arch bridges, said it would be “pretty costly” to improve the strength of bridge structures.

Harvey agreed that the structure of the Oxshott bridge didn’t have “much more than the weight of the bricks” to resist collision, and added that “it would have done a good job stopping a car but not other vehicles”.

The Rail Accident Investigation Branch has confirmed that the lorry was loaded with concrete and weighed approximately 24t.

One possible technique to strengthen the three span bridge, parapet he said, would be to install cantilever restraint up the bridge deck to the side of the bridge piers, on the railway side of the structure. This would comprise vertical steel ribs connected by ties running across the deck to the side of each arch.

The ribs would limit the length of the parapet between substantial supports to about 9m.

Another possible structural solution is to remove the top layer of the brick parapet and drill holes into which are placed either steel or fibreglass bars.

This system of strengthening was devised by a team including Professor Brian Hobbs in 2002. Now with the University of Glamorgan, he said that this system could be put in place in bridges similar to Oxshott, where the parapet was one and a half bricks thick. The system, was endorsed at the time by Railtrack and London Underground but has not yet been installed, he added.

Readers' comments (1)

  • Considering bridge parapets, I was surprised how much is on the public internet, and commercially offered .. .Most of these could not be installed on old/small bridges dotted all over the road network, or perhaps someone commercially minded is working on a retrofit method, as discussed above.
    A sore question would be, how to anchor it to the old bridge, a lot of modification/reinforcement would be required, often within limited headroom. We also have the "listing" brigade to satisfy in some cases.

    Some bridges need complete replacement, or taking out of motor vehicle/highway service altogether.

    "EN 1317 is a performance Specification which lays down requirements for vehicle containment and redirection. The restraint containment level is decided by passing two specified tests in achieving either Normal (N1 or N2), High (H1 H2 H3 ) or Very High Containment (H4a H4b). The UK Highways Agency specifies Normal Containment (N2) for its Trunk Road and Motorway system. . .. "

    Having done what is possible, the rest need PROTECTION from errant lorries/heavy vehicles straying over them, or at least these should be limited to REALLY slow speeds over these bridges, and only used for emergency access, not as a through route. This would need enforcement, e.g. by video cameras.

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