Budget replacement

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Although they are often invisible to users, the most expensive and difficult to install parts of a bridge are the abutments or end seats and the main beams that actually span the gap. New designs, like this timber bridge, aim to prolong the life of these major components.

Rot is the major problem on timber bridges, and any drilled holes will start to rot in time. The decking boards on this sawn timber bridge are fixed to nailing strips that have been tied onto the main beams using galvanised fence wire, not screwed or bolted on. The handrail posts are bolted onto two supports (transoms), not directly to the beam sides, which usually involves drilling holes through each beam. It all means the longevity of main beams is increased and future maintenance should just involve replacing the boards, posts and nailing strips.

nailing strip fixed to beams wth wire ties

It is also possible to extend a bridge's life by using recycled plastic, which can be cut, shaped, screwed and bolted like wood. It is perhaps most useful for the nailing strips and transoms that support the other parts. Recycled plastic is heavier than timber and more flexible, so it is not generally suitable for the decking boards.

handrail support post bolted to transomsBridge handrails always need careful design and secure fixing. People leaning on the rails or horses brushing against them exert a lot of leverage on the posts, which can eventually become loose. The higher the rail is, the worse it gets. Here the transoms (supports) above and below the main beams offer a double fixing for each handrail post. The transoms are positioned at right angles to the main beams to provide added strength and to prevent the posts twisting. The handrail posts are bolted to the transoms. The days of having to fix posts to threaded metal rods passing through the beams are gone!

Find out more...

You can find out more about planning, designing and constructing bridges in the icon Path Bridges Guide.

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