Curved steel bridges--they exist

Ray Haddad wrote:
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The deck is certainly curved, and it looks like some of the supporting girder spans are curved too.
Most curved bridges are actually curved decks supported on a series of straight spans.

Bob, you may be sitting to close to your monitor and have gotten irradiated. That is a curved bridge as I have stood underneath it and attempted to take pictures to show all that *yes* indeed there are curved bridges. This thread came up a year or two ago and I made a special trip to take pix while I was visiting mom. I am going back to Spokane in a couple of weeks and will see if I can get better shots of the steel arc. I am about 50 feet below so I don't know what the Mavica will do and how much I can get.

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Yes it is... I was the one who pointed out this particular bridge in the discussion back then... the girders *are* curved, regardless of what Bob May wants you to believe.
____ Mark the civil engineer

If those girders are indeed cuved, then it is the exception to the rule. The load bearing girders have troubles when trying to support a load in their middle as that is not between the two ends of the girder. You have to do all kinds of rotational support to keep the girder from rolling over on it's side. All the rest of the bridge, the subroadbed and so forth are indeed curved and you can call it a curved bridge but the load supporting girders are not curved. The three photos that have been presented have all had straight girders. Look at the first photo in the earlier post (from on top of the bridge which sweeps up and to the left) and you will note that there is a definite angle (slight but it is there) on the right side of the photo about 3 spans from the edge of the photo where the angles are most pronounced. The last photo is somewhat diffcult to tell but it looks like each span has 11 braces on it (including the ends) and then there is a break in the angle.
-- Why do penguins walk so far to get to their nesting grounds?

Nope, those bridges are straight bridges with a curved trackwork on top. Look at each girder segment and you will see that they are indeed straight. Those girders are the bridge and the stuff (track and so forth) are the load that the bridge is carrying. As with the concrete load that the other poster has shown, the bridge itself is consisting of sequential straight segments that are wide enough to carry the load without tilting over.
-- Why do penguins walk so far to get to their nesting grounds?

wrote:
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You're as blind as you are stubborn. The thing is curved. NOTHING on it is straight. Things have changed in engineering in the last 50 years, really.

I reckon, looking at the photos, that those girders are curved. They'd have to be well braced internally to resist the torsion loads that would be applied to them in addition to the normal bending and shear loads, but this obviously has been done. So, I'll withraw my earlier comment that all steel bridges would have to be made up of tangents if they were to follow a curve. The photos show that in the case of the bridge illustrated, this is not so. Mea Culpa! Regards, Bill.
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itself

On Mon, 08 May 2006 11:00:03 -0700, David Nebenzahl
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I see curved steel girder bridges very often here in West Virginia. If they are used on highways , why can't they be used on railways ?
I have a couple friends who own a bridge construction company. They just finished a bridge over the Logan subdivision on the CSX about a half mile from my house. It's definately curved.
Ken Day

David Nebenzahl wrote:
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OK, I looked at these pics. I've seen them before somewhat larger and clearer printed on good paper. :-)
Those bridges are curved decks supported by s series of straight spans. No problem - just make the spans short enough and wide enough to reduce the transverse bending moment to manageable proportions. Curved bridges of this type are relatively common, but built only when a straight bridge isn't possible.

On Mon, 08 May 2006 11:00:03 -0700, David Nebenzahl
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I see curved steel girder bridges very often here in West Virginia. If they are used on highways , why can't they be used on railways ?
I have a couple friends who own a bridge construction company. They just finished a bridge over the Logan subdivision on the CSX about a half mile from my house. It's definately curved.
Ken Day

"Ken"
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The issue here is the perception of what a "curved" bridge is.
There are hundreds, if not thousands of "curved" steel bridges in the world. However, I'd be very surprised if any of them were made with curved steel girders. How on earth do you curve a steel girder with flanges top and bottom? That'd be one heck of a bending brake. How'd you stop the flanges from buckling?
So, go to that bridge half a mile from your house, stand underneath it and look up. I'd bet the farm that what you'll see are straight girders from pier to pier. Now stand on top of the bridge and the track (And probably the ties) follow a curve.
Yes, this bridge is indeed "curved" but it is made up of straight sections.
-- Cheers
Roger T.
Home of the Great Eastern Railway http://www.highspeedplus.com/~rogertra /

I wrote: -
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I take it all back. I found a site showing how to build and test curved steel girders.
http://www.tfhrc.gov/eventpix/presentation/curvedgirder/index.htm
-- Cheers
Roger T.
Home of the Great Eastern Railway http://www.highspeedplus.com/~rogertra /

Roger T. wrote:
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It's a composite road bridge. The concrete deck plays an important part in keeping the steel girders stable. Furthermore, such large deflections are not allowed on railroad bridges.

On Thu, 11 May 2006 14:38:47 -0700, "Roger T."
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I know what a "curved" girder is.
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Thousands are made with curved steel girders on highways.
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I have, and I've looked down while standing on it and watched the construction day by day as I go by it almost every day,
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You lost your farm :-)
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Ken Day

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What is even more difficult is when the curved bridge is a "box section" with tapered side webs. The geometry required to fabricate those are a nightmare -- especially if the bridge is curving vertically as well as horizontally. ____ Mark

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They can be used on railroads, but there are a couple of factors working against their use:
1) Railroad curves are typically far broader than highway curves, 2) Railroad loads are so large that usually several short spans are more economical than a single long span.
Taking both of those factors together, it means that railroad bridges on curved alignments can usually be built as a series of short, straight spans instead of as an actual curve. But when the need arises, the girders for railroad bridges can be fabricated on a curve.
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You might want to check with them to see if that's really the case. Railroad spans are often so short that they appear curved, when in fact they are made up of a series of short, straight sections between piers.
____ Mark

Mark Mathu wrote:
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One more important factor, and perhaps the most severe restriction: Deflections allowed on railway bridges are much less than on road bridges.

Erik Olsen wrote:
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I don't see it being that "much less" -- my experience is that railroad agencies actually allow more deflection than highway agencies do. Here in Wisconsin USA, I design road and rail bridges for a living and we need to meet the following live load deflection limits for steel bridges: Union Pacific RR: Span Length / 640 Canadian Pacific RR: Span Length / 800 Wisc. Dept. of Trans. highways: Span length / 1200
If you look at what would be considered the "bare bones" deflection criteria as prescribed by AREMA and AASHTO, the limits are: span length / 640 for railroads [AREMA 15.1.2.5] span length / 800 for highways [AASHTO 10.6.2]
As you can see the deflections allowed on railway bridges are larger than on road bridges in the USA, just the opposite of what you wrote.
You seem knowlegable on this subject... what sort of deflection limits are used on steel railroad and highway bridges Denmark? ____ Mark

Mark Mathu wrote:
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Sorry, I wrote based on the situation in Denmark. I didn't imagine that it would be that much different in the USA.
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I don't have any values on hand but I will try to find them.
I remember a design case from 1963 between the isles of Falster and Lolland in the southern part of Denmark. The bridge which was named "Frederik 9th. Bridge", consists of two parallel steel plate girder bridges, a four-lane road bridge and a single-track railway bridge. The bridges are in fact curved, consisting of a nomber of straight spans including a bascule span in each of the bridges.
The road bridge was constructed from RRSt. 52-3 (later Fe510C, tensile strength 510 MPa) whereas the railway bridge was constructed from RRSt. 37-3 (later Fe360C, tensile strength 360 MPa) (sorry, these are DIN and ISO steel designations, I don't know the equivalent US designations). The reason for the different materiels used was that the higher strenght of the RRSt. 52-3 couldn't be utilised on the railway bridge as deflection was the limiting factor.
I participated in rebuilding the track switches and interlocking on the bascule span of the railway bridge around 1985.

Despite that set of specs, I'd bet that the railroad bridges are a lot stiffer than highway bridges. I'll also bet that you can much more freely use concrete in highway bridges than railroad bridges. Being a civil engineer, you know the problems with curved bridges and their loading and difficulty in construction as a result.
-- Why do penguins walk so far to get to their nesting grounds?