Bridge Overpass: Need Opinions

[cv_acr]

For your pleasure
Frankenstein trestle - MEC Mountain Division -  4 degree curve.

Well, that's your typical curved trestle formed from a series a straight spans at a slight angle to each other, and the rails curved on top.

Must be hundreds or thousands of examples like this.

[nkalanaga]

And that picture cuts off the east end!  The entire bridge is, according to one book, 4260 ft long, which would be 26 ft 7.5 inches in N scale, 215 ft high, and has spans up to 160 ft long.  I have no idea what the radius is on the west end, but a 10 degree curve would be 43 inches, and that's a sharp curve for the prototype.  Building it to scale would be a good sized layout in itself, over half the length of our house.

[Ike the BN Freak]

I went on Google Maps, street level and checked it out--sure enough the steel spans are gently curved and appear to be welded in a continuous span with what appear to be expansion joints in the steel structure between the piers. Definitely a first for me. Thanks nkalanaga.

I really need to photo the bridge, just because...

That and its less than 5 minute drive from me.

[nkalanaga]

The Latah Creek Bridge would be perfect for anyone using spline roadbed.  Just glue a detailed "skin" to the roadbed and you're done!  It's a ballasted deck bridge, so the track could be laid and ballasted just like any other.

Of course, it's way too big, but the prototype design could be scaled down.  On a modern layout one or two spans, on shorter piers, wouldn't look out of place.  Maybe on an Ntrak module?  Three tracks, widely spaced, put one in short through trusses (1900), one on traditional deck girder bridges (1950), and one on a modern box girder bridge (today).  Probably no prototype for such a variety at one crossing, but it would attract attention.

[Day One]

Here is a curved concrete bridge.
It's the Multnomah Village bridge located in Portland, OR.
Switching to google street view will let you get a good look at it's structure.

https://goo.gl/maps/mhYd3

It's an old bridge that is rough and bumpy to drive over, and the piers are located close to the edge of the road traveling under it.

[DKS]

Here is a curved concrete bridge.
It's the Multnomah Village bridge located in Portland, OR.
Switching to google street view will let you get a good look at it's structure.

Street view also lets you see that the supporting parts are straight segments.

[primavw]

You guys scared the OP away 

Nah, I've been really busy with work and haven't had time to check the forum. I think I'm going to keep the straight section stored away and scrap the curve. While I wouldn't call myself a bridge engineer, I knew something was kind of strange when I put all of the pieces together. I'm probably going to scoop up a few Rix kits and kitbash them a bit. I will most likely work in a straight span. This thread certainly gave me a lot to consider.

[svedblen]

Here is a curved railroad bridge, in the city of Örnsköldsvik, Sweden. But a very broad curve of course. The support structure seems to be concrete too, but made up of multiple short sections. I have not seen it in person. Only in Google maps.

Satellite view:
https://www.google.com/maps/@63.2927328,18.7029646,481m/data=!3m1!1e3?hl=en

Street view:
https://www.google.com/maps/@63.291983,18.702573,3a,75y,318.86h,81.02t/data=!3m4!1e1!3m2!1sQ9IW5EU8WcRp63P_jBEY5Q!2e0?hl=en

[svedblen]

Here is another one, further north. This one is actually concrete all the way. Clearly seen in street view.

Satellite:
https://www.google.se/maps/place/Ume%C3%A4lven/@63.7651397,20.3293742,3784m/data=!3m1!1e3!4m2!3m1!1s0x467984bd87eabcd7:0xedf98a7641952306

Street view:
https://www.google.se/maps/@63.770122,20.327208,3a,75y,124.22h,100.4t/data=!3m4!1e1!3m2!1sdsd2AtDzzIvyELvDltSOpA!2e0

[jimmo]

Here is a curved railroad bridge, in the city of Örnsköldsvik, Sweden. But a very broad curve of course. The support structure seems to be concrete too, but made up of multiple short sections. I have not seen it in person. Only in Google maps.

Satellite view:
https://www.google.com/maps/@63.2927328,18.7029646,481m/data=!3m1!1e3?hl=en

Street view:
https://www.google.com/maps/@63.291983,18.702573,3a,75y,318.86h,81.02t/data=!3m4!1e1!3m2!1sQ9IW5EU8WcRp63P_jBEY5Q!2e0?hl=en

Both bridges are interesting examples. It appears that they are light rail lines.

[svedblen]

Both bridges are interesting examples. It appears that they are light rail lines.

Actually not. Both examples are from the same line. It is a combined passenger (high speed) and freight line the Bothnia Line. But most pictures show rather short passenger trains that from a distance might perhaps be mistaken for light rail trains.
http://en.m.wikipedia.org/wiki/Bothnia_Line

[glakedylan]

The Keystone Viaduct, like 99.9% of all "curved" bridges, is (or was) comprised of a series of straight spans.  When the state road was straightened and a pier was removed, a faux curved span was installed, but it only has to carry bicycles.

Lee

thanks Lee for the history
good to know
much appreciated

Gary

[nkalanaga]

One thing that curved railway bridges seem to have in common are that they're "continous" bridges.  The few I've seen don't have structurally separate spans, instead having all of the spans fastened together to make a single curved "beam".  That allows the load outside the pier-pier line to balanced by the mass of the bridge (and train) on the remainder of the curve.  I don't know whether this is a result of better materials allowing the elimination of expansion and stress relief gaps between spans, or because we can transport and assemble bigger pieces today.

[Bruce Bird]

No- better engineering.  The older rail bridges with straight spans on a slight curve were built that way to allow for expansion in each span- one end is fixed and the other is allowed to move (expansion end).  With newer bridges you can have a solid beam construction with various fixed piers with expansion piers in between the fixed ones.

And I looked at Latah on Streetview as well and it may be smooth but it isn't welded.  You can easily see bolted connections and splice plates on the beams.  The splice plates are inside the beams to help the bridge look smooth.  The various lengths of beams were delivered to the site and bolted together just like any steel frame bridge.

When I get a chance I will post pics of what a fixed and expansion bearing look like.  There are many different type of designs.

Bruce

[nkalanaga]

Bruce:  Thank you.  I just assumed the bridge was welded, as much new construction seems to be.  Driving by on I-90 doesn't give much time for looking, and since I don't model Spokane, there hasn't been any reason to examine the bridge too closely.

Mallery's "Bridge and Trestle Handbook" (is it still in print?) has a nice section on shoes and bearings, but I imagine it's as dated as the rest of the book.  My copy was published in 1976 and doesn't mention Latah Creek.  It just says "don't curve your spans".