Viaduct terminology.

[30907]

(This is actually about a French viaduct but I think this forum is the best place for it).

Does anyone happen to know the English term for the pizza-slice shaped voids between the arches in the attached photo of Morez viaduct? They serve to lighten the structure - in French they are élégissement.

(Enquiry from my sister's translation forum - thanks in advance)

@timmydunn

 

[Dr Hoo]

I’ve heard them described as ‘sinuses’. [I am not an engineer.]

 

[The exile]

Are they not spandrels? Or are they only that if filled in?

 

[stuving]

I guess it's an open spandrel. Usually that means the spandrel is replaced by a mini-viaduct, with pillars or arches to hold up the bridge deck. But a small hole needing no supports in it appears to fit.

 

[Mcr Warrior]

I was going to say "ventilation" but doubtful that would have been correct! BTW, noting that the example posted by @30907 is from France, were similar features (i.e. the voids) ever that commonplace on GB (railway) viaducts?

 

[30907]

I was going to say "ventilation" but doubtful that would have been correct! BTW, noting that the example posted by @30907 is from France, were similar features (i.e. the voids) ever that commonplace on GB (railway) viaducts?

I can't think of anywhere with that particular style of viaduct - it seems characteristically Alpine to me. I could imagine the odd decorative void in a C18th bridge - or there's the piers of the Ouse Valley Viaduct on the Brighton line but that's not strictly comparable.

 

[Dr Hoo]

Such ‘holes’ were used to reduce the weight of a structure even before the time of railways.
The famous bridge at Pontypridd (once claimed to be the longest arch in the world) has them after previous versions collapsed.
Marple Aqueduct is another early example of an ‘orificed’ design.

 

[30907]

I guess it's an open spandrel. Usually that means the spandrel is replaced by a mini-viaduct, with pillars or arches to hold up the bridge deck. But a small hole needing no supports in it appears to fit.

Thanks - I've forwarded the suggestion along with

pierced spandrel

As the translation is of a rail travel book, rather than a treatise on viaducts it may be good enough.

My sister's contact says thank you

 

[eastwestdivide]

Marple Aqueduct

Quoted in a book I can‘t find at the moment as having ‘pierced spandrels’ - the phrase sticks in my mind even if the location of the book doesn’t!

 

[DelW]

In "Great Buildings of the World: Bridges", Derrick Beckett refers to both "open" and "pierced" spandrels, the examples shown having arched openings.

In "How to read Bridges", Edward Denison and Ian Stewart refer only to "open" spandrels for both arched and cylindrical openings.

So I think you're okay with either!

 

[Ken X]

Just our of interest, I spotted this pierced railway viaduct whilst leaving Worcester on the Worcester and Birmingham Canal in July, wondered what the reason was for the circular hole, so took a quick happy snap. Can I assume it is weight saving, as mentioned earlier, or is there another explanation?

 

[Dr Hoo]

It may also help to diffuse the sideways thrust of the large arch.

 

[30907]

Thanks everyone. I knew I'd seen a railway bridge with open/pierced spandrel somewhere.

 

[stuving]

It may also help to diffuse the sideways thrust of the large arch.

I think the question to ask is where would the weight of the missing masonry be borne. Here, it would not carry down to the ground, but be redirected sideways by the arch. On one side that would push the abutment, but on the other it would push the base of the main arch and the pier below, which is much less solid. So I'd suggest that's the advantage of the big hole (whatever it's called).

 

[edwin_m]

Because the side arch is smaller than the main one, the weight acting downwards on it will be re-directed sideways into the intermediate pier (left to right in that photo) at a lower level than that from the main arch (right to left). This would possibly increase the risk of pier collapse, particularly as the trench of the canal is a short distance to the right of the pier foundations. The hole reduces the total weight force as mentioned, but also directs some of it into the pier at approximately the same level as the opposing force from the main arch, thus reducing the uneven force distribution.

 

[Ken X]

Many thanks for the replies, it interested me at the time (which probably indicates I should get out more ) and this thread seemed a good opportunity to ask the question.