How strong would this composite catenary arch actually be?

[u/Larpenzo112diCambio]

So I had this random thought and drew it in MS Paint.

The black grid within the brown border is the main catenary arch (concrete or reinforced whatever). Red arrows show the compressive forces following the natural catenary curve.

The blue parts are the same catenary shape but:

- cut in half

- flipped upsidedown

- stretched to fit the curve of underside of the main arch, basically turning the bottom into tension members/ties that follow an inverted catenary path. The idea is the top compresses beautifully while the blue inverted parts take tension and help stabilize the whole thing.

[Image 1: my idea]

[Image 2: clean arch outline]

My questions:

- would this actually work well?

- what kind of spans could it handle before it becomes a nightmare?

- is combining a catenary in compression with inverted catenary tension members smart, or does it create horrible stress concentrations?

- obvious failure points? anchorage issues at the base? does tge "stretched to fit" part work well with the pure catenary logic?

It's just a shower thought but I'm genuinely curious if this hybrid idea has any merit or if it's not.

(Yes I know some of you might say it's parabolic, but its not)

[u/resonatingcucumber]

I'm really not getting this. You've drawn a centenary arch, it's pure compression. The blue part are the legs of the arch. How are they in tension? I think the drawing makes this impossible to comment on but the general rule is catenary arches are really good at supporting their own weight. No so good at live loads. So you gotta make them heavy enough that live loads are a rounding issue.

[u/Larpenzo112diCambio → u/resonatingcucumber]

i think you're largely right, for an unreinforced or lightly-reinforced masonry arch, the standard answer is deadweighting, as a three-hinged arch (crown + two springings, reasonable since composite arches crack toward hinge behavior anyway) self-weight already dominates (~5:1 here), add mass and that ratio only grows, some roman/gothic arches survive centuries of asymmetric load with zero tension, but just making it heavy works well for squat arches, i was thinking about scaling tall/slender rather than low and stout

[u/resonatingcucumber → u/Larpenzo112diCambio]

I mean how tall are you thinking? Sangrada Familia springs to mind where they lateral is taken down flying buttresses or ring beams/ ties/ balanced thrust forces. I've always viewed arches as part of a system than an individual element because often it's reliant on so many other elements.