Thursday, 21 July 2011

Borough High Street bridge

Not quite new, this tubular steel truss bridge went up over the Easter bank holiday weekend. It took several months to build, of course, but the engineers worked out that they could build it on top of the newly-constructed viaduct alongside, where it could be worked on without disrupting traffic. The new railway viaduct has caused a lot of disruption to Borough Market, but that's another story. The original plan was to construct the whole thing some way down Southwark Street, and transport it up the road to its final position, where it takes two lines into London Bridge station. That plan fell foul of the network of underground services and tube lines that could be damaged by imposing such a heavy load on the road surface. So, the bridge was assembled high up on the viaduct, on temporary rails that would allow it to move to the final position. Over the holiday weekend 22 to 25 April the road was closed and the structure inched across at a snail's pace, supported on hi-tech motorised platforms, and then lowered into position. Too slow to stand around watching really, but Network Rail have put a time-lapse video on YouTube. The bowstring truss is just the public face of the bridge: the other side is hard up against the old railway bridge and it's just a flat girder, albeit massive. The aggressively muscular truss side is designed for effect, and not everyone will love it.

It comes as a surprise to find that no trains will use the bridge until work on London Bridge station is complete, some years hence. When everything is in place, though, this will be a vital part of the new Crossrail link currently under construction across central London.

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