Bonds Mill Bridge

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Bonds Mill Bridge was opened in 1994 and is the world's first plastic road bridge.


The original swing bridge was still in place in 1993 but in a very poor state. It was of stell construction but had been widened and partially re-inforced following the disuse of the canal.

The main RSJs were such poor that it was possible to put one's fist through them in places.

The original plan was to install a couter balanced steel lift bridge but the supplier decided to triple the cost over and above their original estimate.

It was at this point that Maunsell's suggested to the Cotswold Canals Trust that we consider using a bridge based on recent development work they had undertaken on composite bridges.

Some large section structural beams had been fabricated and one of these had been tested to destruction; a second one was available for use at Bond's Mill.

The main advantages in using such a bridge was:

• Lighter Weight: This allowed the use of the original abutments and the need for overhead counter weights could be eliminated.

• Low Maintenance: No wood to rot or metal to rust paint.
  

The Cotswold Canals Trust repaired and modified the abutments and the bridge was installed by WRG with the assistance of Maunsells.

The hydraulics were designed and installed by Hydatight.

There have been a number of problems with the bridge, some foreseeable and some not. The hydraulics initially caused problems and a review of the design indicated that the design was not really powerful enough to do the job. Another initial issue was the need to ensure that the rams on both sides applied and equal strength and travelled the same distance as failure to do this would twist the bridge.

There was a major problem with vibration as the bridge descended when it was first installed. Eventually this was tracked down to air being trapped in the rams which need to be detached from the bridge in order to get all the air out.

There wer also problems with the roadway. At first the steel edging on the towpath became loose and was only fxed on the second attempt. The second problem was more serious; the road deck became spongy after a period of use.

The road deck consists of a wearing surface which comprises a rubbery material on a plywood base. This is supported on wide transverse beams about 10cm deep the inside of which is filled with foam plastic within a cell structure. Tests by Surrey Unicersity suggested that this design should work even for HA loadings - experience suggests otherwise!



More details about the bridge can be found at : http://iti.acns.nwu.edu/composites/problem.html