Tag Archives: arch

The dangers of canal bridges …

… to Her Majesty’s mails.

Skew arch bridges

The IHAI AGM at the weekend, in Newtownabbey Borough Council’s splendidly restored Mossley Mill,  included a tour of the premises and its museum. Then Professor Adrian Long of Queen’s University Belfast gave a short talk about the FlexiArch bridge, which his team have been developing since the 1990s.

Professor Adrian Long with a wooden model of the FlexiArch bridge

He said that their work started by asking why nobody built arched bridges any more; they developed a system that used pre-cast voussoirs (the wedge-shaped blocks) linked by a polymeric flexible membrane. The voussoirs for any bridge are cast to give the correct taper for the span and rise required for that bridge.

Arch rings arrive on site stowed flat on the back of a truck; when they are lifted off, they fall into the correct shape and are lowered into position on previously-installed footings. Each arch ring is 1m wide; several of them can be placed side by side to give whatever width is required. The end walls are added and the structure is filled and given the appropriate surface (eg tarmac).

FlexiArch is manufactured by Macrete of Toomebridge (beside Lough Neagh); their website shows several examples of installation including one at a name familiar on Irish waterways. There is a brochure [PDF] and there is a video showing the installation of a 15-metre bridge.

Wooden model as a skew arch

No, I haven’t any shares in it. I just thought it was interesting, for three reasons: first, the speed of construction is very impressive; second, there is a link to Lough Neagh; third, it might encourage the construction of more skew arch bridges over canals.


Who took the arch? A Shannon whodunnit

O’Briensbridge is a village in Co Clare, islanded between the headrace of the Ardnacrusha hydroelectric power station and the River Shannon. Up to 1929 the river was the navigation between Limerick and Lough Derg (and eventually Dublin), and the bridge itself was something of an obstacle to navigation.

In 1832 the engineer Thomas Rhodes drew a sketch of the bridge with 14 arches, whereas nowadays it has only 12. We know when the seven arches on the Co Limerick side were reduced to six, but it has not been clear when an arch was removed from the Clare side. I think I know the answer; you can read it here.