Curved steel bridges--they exist

On Tue, 9 May 2006 18:37:46 -0700, I said, "Pick a card, any card" and Steve Caple instead replied:
The bridge is curved. Period. The girders are also curved but that is irrelevant. The photo shows a curved bridge. You'd be correct if I were discussing the girders supporting the concrete. There are better views of that curvature. -- Ray

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.

Sure looks like the girders themselves are straight sections! The angle isn't much and the photo isn't the best but I do see that the girders themselves are indeed straight. It looks like every 11 posts in the girder, the angle changes. Kindo of hard to tell tho as the photo is rather fuzzy.
-- Why do penguins walk so far to get to their nesting grounds?

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?

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

On Wed, 10 May 2006 19:25:06 -0700, I said, "Pick a card, any card" and "Bob May" instead replied:
Study the gap between the edge of the girder and the edge of the curved bridge. Since the distance is constant, at least from the photographer's angle, the curves must be the same. -- Ray

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.

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.

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"
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

I wrote: -
I take it all back. I found a site showing how to build and test curved steel girders.

-- Cheers
Roger T.
Home of the Great Eastern Railway

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.

I know what a "curved" girder is.
Thousands are made with curved steel girders on highways. 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,
You lost your farm :-)
Ken Day

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.
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

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

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

On Fri, 12 May 2006 05:56:34 GMT, I said, "Pick a card, any card" and "Mark Mathu" instead replied:
Like highway curves, my bet is they're also banked to allow higher transit speed but increasing friction at the same time. An engineer's nightmare but as the photos show, can be accomplished.
They compensate by making the boxcars and other load bearing cars straight.
Mathematically speaking, all curves are an infinite number of straight line segments formulaically defined in this link Remember, this is analytical geometry. Nothing on this page is easy. An arc, which is what is really being discussed in this thread, is a segment of the circle defined above which is mathematically explained in that link.
Here's an arc definition and description. last, a chord: A thousand or so years ago, as a young engineering student, we had to be multi disciplined after a fashion by being exposed to a variety of engineering subjects. I was an Electronics Engineer but had to suffer through some Mechanical, Civil, Hydraulic and Electrical before I was allowed to choose my final discipline.
We designed bridges of all types but none of them were curved, I'm afraid. I know it can be done as we have seen proof in the photos. It strikes me as odd that in the face of evidence, we still cannot agree that a curve bridge can and does exist.
It reminds me of the Flat Earth Society in a strange way. -- Ray

I used to read reports of a "Man Will Never Fly" group in Kitty Hawk NC (site of Wright brothers' first flights) with the motto: "Birds fly, Men drink"!

Of course you and I know that it is a vast conspiracy to doctor those photos to make it look as if the steel structure is curved. The lengths that some people will go to...
fl@liner