The Flexi Arch Bridge System

Although the arch bridge is almost as old as the bridge they are not generally used for modern military bridging, even non equipment bridging. Developed in conjunction with Queens University Belfast, the Flexi Arch bridge system from Macrete uses precast concrete sections to dramatically improve installation time.

Arches are strong, robust and look good but they are labour intensive and expensive because they need formwork in order to centre the bridge and strong abutments to transfer the loads.

Arch bridge centering
Arch bridge centering

By using the flatpack precast Flexi Arch with their precast voussoirs a durable and long life bridge without corrodible reinforcement can be built.

Once the foundations have been built the arch is lifted in, spandrel walls attached and concrete fill poured. The road surface and cladding can then be finished. Typical build times for a 15m arch are less than a day. The maximum span is limited by transport and crane lifting capacity but they are already developing a double radius arch for rail profiles.

Perhaps not of enormous relevance to the military bridge builder but interesting nonetheless and good to know bridge building innovation is still alive and well in the UK.

Read more at MacreteQueens University and Google


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February 9, 2015 9:03 am

I struggle to see the advantage?
– specialist facility ror making the components
– hence v long transfer to point of need
– v bulky (and specialist) kit to move and erect it
– no time (speed) advantage, even forgetting all of the above

Maybe material is cheap and maintenance free, but…

February 9, 2015 9:24 am

I think the advantage is that when you look at the video, all the preparation work on site is done away from the river/ canal / railway line etc, so you are not impeding the flow of whatever it is you are bridging.
From a commercial point of view, 6 40 foot trailers in and out in a day, and the hire of a crane for the day, it probably a lot cheaper and less disturbing that have a load of guys building form work, then getting them to pour concrete. It also has the advantage that the more you can do “inside” a factory, the less time you may loose due to bad weather.
As TD says, possibly little application for the military, but a great bit of British Engineering

February 9, 2015 10:15 am

The issue politely glossed over is that the strength of an arched bridge is all in the foundations. The point (as in reason) of the arch is that all forces act as compression though the arch – no tensile force at all – down to the base of the arch. If the foundations are weak or mobile due to misunderstood ground mechanics or poor implementation, the arch will fall. Making a structure of tapered blocks strong in compression is relatively straightforward, although it has to be said the idea of sticking them to a band so they can be lifted as one onto the prepared footings is pretty impressive.

February 9, 2015 1:04 pm

For defence I’d see this more as a reconstruction tool; building bridges in areas where you want your exposure time in the field to be minimised.

What I don’t understand is how flexible the construction is; wouldn’t you need to shape each block to match the span of the bridge?

February 9, 2015 4:31 pm

Quite a clever idea, I could see it having use in post disaster and conflict reconstruction, maybe DFID should take a look.


I think you provide them with the span dimensions and they provide the required arch and abutment’s, says they can span from 3m up to 15m in the video.

February 9, 2015 4:58 pm

I had to Google “voussoir” as I couldn’t work out what something that sounded French infantry-ish had to do with bridges.

“A voussoir (pronounced /vuˈswɑr/) is a wedge-shaped element, typically a stone, used in building an arch or vault.”

Deja Vu
Deja Vu
February 9, 2015 5:43 pm

Steve D

Yes I believe though it is not stated that the arches can be tailored any way you want, as the individual voussoirs are presumably cast in steel moulds that can be adjusted for any curve by adjusting the slope of the sides.

If all the voussoirs have the same angle the arch will be circular, but parabolic would just be a matter of having maybe three or four changes of angle probably.

A Different Gareth
A Different Gareth
February 10, 2015 1:03 pm

Might be handy for building bunkers/shelters? With some holes in the blocks to allow lateral connections of some sort you could build an arched shelter pretty quickly. If it wasn’t going to be a bridge presumably the blocks could be smaller and/or aerated concrete? Cover it with concrete canvas to make it watertight.

The strips of big blocks, if laid on their side, could be used as a kind of concrete Armco barrier to contain vehicle movements.

Maybe you could use it for quickly and consistently making brick arches. A prefabricated sheet of bricks and mortar that when you lift it up forms the arch and squeezes out any excess mortar.

I wonder if these would be of use for making paths in soft ground, perhaps using T-shaped blocks to get some depth and also spread the weight of vehicles.

February 11, 2015 6:55 am

Brings to mind the precast segments used to line underground rail tunnels.