Tuesday, March 17, 2015

Always have a good platform to work from.



Some dry stone bridges can be built without having to construct temporary bridges either side to work off of. This bridge in Russell Ontario had very little rise and the creek it went over was dry so our team could build the bridge and transport material across with no trouble. 



Bruce's Bridge had a steady stream going under the form while it was being built. The old wooden bridge was used as the new temporary platform while we built the new stone bridge.


At Hubb Creek Bridge in Prince Edward County we laid planks over the big barn beams that were supporting the bridge form in order to walk and carry material across to the other side.


You can see here too that because our 2x4s extended several inches past the form, radiating lines for the alignment of all the voussoirs had to be set up with strings, rather than try to follow the lines drawn on the plywood.



3 comments:

  1. John, this has always concerned me, since the building of the Hubb Creek bridge.
    In the photo of Bruce's bridge, you can see some very tall voussoir stones placed higher in the arch. If very tall stones are placed nearer/closer to the apex of the arch, the contour of the uphill climb steepens and it becomes a difficult bridge to climb. Anne Halliday remarked she needed to extend her bridge by a meter to make it easier for the golfers to climb. Please correct or confirm. It seems that the volume of material necessary to fill then must also increase, if even one tall stone gets placed nearer the top. Shouldn't the long/tall voussoirs be placed early or split/shortened before they 'rise to the occasion" bw

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  2. Yes that's right. Of course there is nothing wrong with extending the bridge to make it not so steep, if you have the material. Also it could be argued that voussoirs near the apex are laid more upright and thus more likely to slip downward than ones nearer the skewback which are laid more flat which in a way appears almost corbelled. This would tempt one to make the upper 'more upright' voussoirs longer, so that there would be more 'meat' on them for the neighbouring arch stones to clamp on to .

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  3. another solution witnessed in Norman's bridge seems that the semi-circle of the arch begins below grade of the surrounding bank. bw

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