Talk:Self-anchored suspension bridge

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[edit] self-anchored vs self-supporting?

Hi all, I changed the image on this page from the proposed bay bridge to the Pittsburgh three sisters. I'm thinking there perhaps there should be some discussion about the differences between the old-fashioned two-tower self-anchored suspension bridge and the more modern single-tower self-supporting suspension span as proposed for the bay bridge. Are there other examples of these types of bridges we could look at to get a better idea of how to approach this issue?

Thanks, Robshill 18:56, 20 April 2006 (UTC)

Currently, the largest Self-anchored suspension bridge is the Yeong Jong Bridge. Its website has quite a bit of information on this topic. I'll add something about this to the article as well. -- Samuel Wantman 07:50, 21 April 2006 (UTC)

I'd like to learn more about self anchored vs. self supporting. To me the key point about self anchored is that the roadway ends up in compression much more than it would if there were anchorages, and that the cables themselves are conventional heavy cables that follow heavily bowed paths (not a catenary exactly) with separate suspenders in tension like a "normal" suspension bridge. What is self supporting exactly? How does it differ from a cable stayed? The Yeong Jong reminds me of a cable stayed like the new Charles River bridge (Zakim Bunker Hill Bridge) in Boston (it even has similar shaped towers)... ++Lar: t/c 17:32, 21 April 2006 (UTC)

My apologies, please bear with me while I back off a bit and approach this from a different direction. Simply put, a self-anchored suspension bridge lacks anchorages -- the apartment-building-sized huge chunks of concrete which keep the cables from pulling out of the earth. Instead, the cables attach to the road deck, which experiences compression equal to the tension in the cables. However, the first sentence of the article is "A self-anchored suspension bridge is a type of bridge combining elements of a suspended-deck suspension bridge and a cable-stayed bridge." I think this sentence is wrong and should be changed, but I think I can see why it was put there.

This article describes the new span on the bay bridge, which by my definition above is a self-anchored suspension bridge, because it is a suspension bridge which lacks anchorages and has the deck in compression. But if you take a close look at the pictures, you notice two things about the bridge which remind one of a cable-stayed bridge. First, there is only one tower. Second, the suspender wires are not vertical -- they slant down at an angle. My theory is that the initial author of the self-anchored suspension bridge article focused on these cable-stayed-bridge-like elements of the new bay bridge.

Since we now know that there are many self-anchored suspension bridges which in no way resemble cable-stayed bridges, I think we should reword the article to focus on the key feature of self-anchored bridges: the lack of anchorages. Let's excise the term "self supporting suspension bridge" everywhere, and replace it with "self-anchored suspension bridge".

Robshill 04:16, 22 April 2006 (UTC)

Thanks for the restatement from fundamentals. I personally knew all that already but wasn't nearly as clear as you in putting it crisply and succinctly. With that as background (and much of it ought to be worked into the article, i think, it's that good), I agree. Let's get the point across that self anchored and cable stayed are different, that we're not talking about cable stayed and that self supporting, if anything other than just a confusing term to be avoided completely, is a broader category than this one as it could possibly include both types. Or just not mention it at all. Vertical suspenders to me are key. IIRC User:Samuel Wantman(??) did some diagrams about bridge phylogeny that may be good to reference. ++Lar: t/c 05:38, 22 April 2006 (UTC)

The diagrams were from User:Leonard G. -- Samuel Wantman 06:09, 22 April 2006 (UTC)

A couple of notes...the self-anchored suspension bridge predates the cable-stayed bridge (which appeared c1950 in Germany [1]), so we ought not say that it combines elements of the suspension and cable-stayed types. Also, I'm thinking vertical hangers are not definitive of suspension bridges; the Severn bridge appears to have diagonal hangers (see bottom photo in article). I think that as long as the hangers connect a catenary-like cable to the deck, it's a suspension bridge. If the hangers connect the deck to the tower, it's a cable-stayed bridge. —The preceding unsigned comment was added by Robshill (talk • contribs) 01:44, 22 April 2006.

Nod. Nice work on the rewrite! Thanks for the correction on the graphs too, Sam. I do not think vertical suspendors are mandatory in the definition I guess... Aside (while we are talking about bridge phylogeny), what is the Brooklyn Bridge? It has a lot of non vertical cabling in it but does it have any direct cable stays to the towers?. Also consider the Royal Albert Bridge which uses suspension chains in tandem with a compression arch to put no net sideways loadings on its end towers. Not exactly a self anchored since it's not the roadway carrying it. There are so many variants! Cool stuff. ++Lar: t/c 16:37, 22 April 2006 (UTC)

PS the Severn's diagonal hangers are diagonal in the vertical plane orthogonal to the main cables (and roadway) but are still vertical in the plane congruent to the main cables (if you look at the bridge square on in a sideways view, they would look vertical). Cable stayed bridges typically are not because the cables run diagonally from the tower to the roadway. That's what I was referring to, not true verticality in all planes... being vertical in the plane congruent to the main cables means they are not themselves exerting any sideways to the cable force, and being paired means they are not exerting any force that moves the cable sideways either (the sum of their force is straight down). If that makes any sense! I am not sure! ++Lar: t/c 16:43, 22 April 2006 (UTC)