Bridge Overpass: Need Opinions

[wazzou]

How about a two lane, rural, old cast concrete bridge on a modest curve at the end of the structure?

I've seen quite a few examples like this here in the Pacific NW.

https://www.google.com/maps/@46.666657,-122.980602,3a,75y,90h,82.59t/data=!3m4!1e1!3m2!1s6SuAZ-p4ikZZJBrig1w5-A!2e0
https://www.google.com/maps/@46.666441,-122.98015,3a,75y,311.76h,80.97t/data=!3m4!1e1!3m2!1sVHSbvsmcARCGbYWX6Y8fSg!2e0

But, that's about the extent of it.

[jimmo]

Also, any joints between cast bridge sections should be directly supported on one of the vertical supports. You can't have a joint free hanging in mid air between supports. (At least not on a real bridge.)

Really takes me out of it when I see all these model bridges with major supports under the middle of a girder span, and unsupported girder joints in the middle of the bridge.

Don't get me started...

I had a Paul Mallery's book "Bridge and Trestle Handbook" years ago and in the back of the book there was a page of illustrations entitled (something like), "Model bridge comedy of errors," it made a huge impact on my view of building model bridges.

If this forum were a university (IMHO) it should be required reading. Especially after seeing the bridge and tunnel thread elsewhere in this forum. Some of you guys are great modelers but could use a little more info on the subject of bridges.

[jimmo]

How about a two lane, rural, old cast concrete bridge on a modest curve at the end of the structure?

The key word here is "modest curve." There is no shortage of curved concrete bridges, especially in places where there are freeway overpasses and interchanges, the important thing to bear in mind is the support system and where they are located.

Unless you are designing a fast food drive-through, extremely tight curves should be avoided. David's solution was following common sense engineering practices and is a great example of a plausible model bridge.

[wazzou]

The key word here is "modest curve." There is no shortage of curved concrete bridges, especially in places where there are freeway overpasses and interchanges, the important thing to bear in mind is the support system and where they are located.

Unless you are designing a fast food drive-through, extremely tight curves should be avoided. David's solution was following common sense engineering practices and is a great example of a plausible model bridge.

Yeah, I get it Jim.

[DKS]

How about a two lane, rural, old cast concrete bridge on a modest curve at the end of the structure?

I've seen quite a few examples like this here in the Pacific NW.

https://www.google.com/maps/@46.666657,-122.980602,3a,75y,90h,82.59t/data=!3m4!1e1!3m2!1s6SuAZ-p4ikZZJBrig1w5-A!2e0
https://www.google.com/maps/@46.666441,-122.98015,3a,75y,311.76h,80.97t/data=!3m4!1e1!3m2!1sVHSbvsmcARCGbYWX6Y8fSg!2e0

But, that's about the extent of it.

Excellent. Glad you posted this. Being so short and slight, the curve seems almost superfluous, as though it's really just to smooth the approach--nothing much projecting beyond the limits of the abutments other than the railing.

Don't get me started...

I hear you. Implausible bridges are probably my biggest pet peeve.

[peteski]

Really takes me out of it when I see all these model bridges with major supports under the middle of a girder span, and unsupported girder joints in the middle of the bridge.

Like this curved N scale beauty?  The missing support is elsewhere, but still, it is just laughable on so many levles.

[mrhedley]

How about balsa or bass wood?  You can get it in wider thickness that will be much easier to work with than the same size Stryene.  A little fine sanding will provide enough texture that resembles the coarseness of the concrete.  Apply a seal coat before painting and apply enough paint to keep any grain pattern from showing through.  I make my abutments and supports out of it and I like how they appear.  Unfortunately I'm still having Photobucket problems or I'd post a pic for you.

[peteski]

How about balsa or bass wood?  You can get it in wider thickness that will be much easier to work with than the same size Stryene.  A little fine sanding will provide enough texture that resembles the coarseness of the concrete.  Apply a seal coat before painting and apply enough paint to keep any grain pattern from showing through.  I make my abutments and supports out of it and I like how they appear.  Unfortunately I'm still having Photobucket problems or I'd post a pic for you.

Balsa might be a bit soft, but basswood works ok.  Here is a photo of friend's concrete bridge. Piers are made from basswood.

[cv_acr]

I've seen plenty of curved road bridges, but the only ones I've seen were steel deck girder, not cast concrete. I'd be interested in seeing one of these.

[DKS]

Awesome. Thank you. Pretty funky markings on the thing...

How about balsa or bass wood?  You can get it in wider thickness that will be much easier to work with than the same size Stryene.  A little fine sanding will provide enough texture that resembles the coarseness of the concrete.

Balsa may be easier to work, but control is poor; concrete structures such as bridges and abutments are made of precise geometric shapes, and balsa is difficult to shape with the needed precision, not to mention the surface is very porous and would need to be sealed. Also, the "coarseness of concrete," when reduced 160 times, becomes quite smooth. Modelers often make the mistake of thinking that objects with somewhat rough surfaces in real life should also have rough surfaces as models. Unfortunately, that's not the case; a slightly grainy coat of paint is all you really need to simulate the surface of concrete. Styrene is an ideal material to use (and not as hard to work as some may think); basswood is adequate, assuming the surfaces are sanded smooth and sealed.

[Kentuckian]

There is a difference between cast concrete and pre-cast, segmental bridges, like the example above.

[jimmo]

Balsa might be a bit soft, but basswood works ok.  Here is a photo of friend's concrete bridge. Piers are made from basswood.

Nice looking prestressed concrete bridge model. I would love to see the prototype. In all my years of being a rail fan, modeler and bridge aficionado, I have never seen a curved concrete railroad bridge. Lots of curved concrete highway bridges (especially here in California) even a light rail or two but not a single one was carrying heavy standard gauge rail line.

[jimmo]

Great example of a curved concrete bridge but how do we know it's a railroad bridge? Light rail lines do not count as their load rating is similar to highway standards.

[peteski]

Nice looking prestressed concrete bridge model. I would love to see the prototype. In all my years of being a rail fan, modeler and bridge aficionado, I have never seen a curved concrete railroad bridge. Lots of curved concrete highway bridges (especially here in California) even a light rail or two but not a single one was carrying heavy standard gauge rail line.

It is totally freelanced.  The curved concrete deck is supported by steel beams resting on the piers.  The beams are painted green (not easily seen in that photo).

[jimmo]

It is totally freelanced.  The curved concrete deck is supported by steel beams resting on the piers.  The beams are painted green (not easily seen in that photo).

I see the straight steel beams now, obviously your friend did his homework before taking on the task. The results are convincing.