Bridge Overpass: Need Opinions

[primavw]

About two weeks ago, I started the project of scratch-building a bridge overpass. I planned on using Hydrocal to attempt to accomplish the texture of concrete. I used styrene to make the forms to cast the hydrocal, and everything seemed to be working ok.

My complaint now that they are ready to be installed, is the uprights which support the curved section over the rails is going to take up a bit too much real-estate and will cause some rubbing with wider rolling stock. Very minor. The other is that I will need to do some minor filling to get the two pieces to fit together without gaps.

Anyway, I just need a general opinion. I'm kind of on the fence about pushing forward with the hydrocal casts, and am possibly considering scrapping them and just picking up some boring old Rix kits to complete these.

Anyway, take a look and let me know what you think.



The center support is not installed for this shot.


Loosely based on this:


Keep in mind they are just set in place, so they aren't aligned properly. Also the pavement has not been painted on so that area has just a rough layer of paint.

[John]

I would follow to the proptype .. make it straight .. and build the support like the picture you have .. more believable ..

[DKS]

Have not seen an all-concrete curved bridge... at least one that sharply curved. Think in terms of where weight will be supported--and you'll realize the bridge would quickly topple if built in real life.

Try something like this:

[wazzou]

It's certainly not necessary to use concrete to make concrete. 
It looks easy enough to construct from Styrene, then paint and weather to resemble concrete.
I'd ditch the harsh curve too.

[DKS]

It's certainly not necessary to use concrete to make concrete. 
It looks easy enough to construct from Styrene, then paint and weather to resemble concrete.

This.

[davefoxx]

I was going to also suggest to go with straight spans on a less angled centerline, as John and DKS suggested, but then DKS posted a picture exactly of what I had envisioned.  I can't top that.

If you do decide to go back to the boring old Rix kits, you can skew the parts.  I used sheet styrene to make the sloping abutment.  (Please disregard the lack of weathering.  I haven't set this bridge permanently yet.)



DFF

[tom mann]

I would build what DKS has drawn.  A concrete bridge with that sharp of a curve doesn't look right.

[Kentuckian]

I like what DKS said.  Curved concrete bridges are very rare.  And railroads like to have a clear zone to abutments.  In most cases, the railroad was there before the highway, and the highway dept. needs an airspace permit from the railroad to build a bridge over it.  So as part of the permit process, the railroad gets to specify a clear zone.  This is in case of a derailment at the overpass.  Era would play a role here, an older era may have less of a clear zone.

BTW, railroads usually take their time with a permit review, since the bridge construction is a pain for them.  The last one I aware of happened recently, and it took several years.

[Bruce Bird]

From someone who designs and builds these things in real life- I agree completely with the concept of a straight bridge.  Also, the castings are a bit Fred-Flinstone-ish: very chunky.  You could probably re-use the piers, but shave those puppies down to no more than 18-24 scale inches wide.  No need to be wider than that.  Curved concrete bridges are not impossible to design, but the stresses and forces in the beams plus the difficulty of building it properly in the field make it almost a last-chance design choice when building a bridge.  Make it straight and make your scale engineers, carpenters, ironworkers, and laborers happy!

Also, your era would dictate what type of pier design to use.  Current standards call for a solid pier up to a minimum height, so that if a train derails under the bridge it hits a 'crash wall' and doesn't knock out a pier piling and collapse the bridge.  I think the minimum height is 20 feet.  Older piers would have the open pilings.  Your pier designs are perfect for a modern layout.

Bruce
BTW - your proto pics show a bridge with steel girder superstructure holding up a cast-in-place concrete deck.  A very common design.

[Chris333]

I use fine texture spray paint on concrete made of styrene. The color of the texture doesn't matter because you can spray to correct color over it.





Oh yeah, I'd make it straight as well 

[jimmo]

Wow, you guys pretty much nailed my sediments.

If you're using the photo for your concrete color guide, remember that you are looking at it in a hard shadow so your model bridge is way too dark. It is best to always err on the lighter-toned side as it is far easier to darken that it is to lighten a painted surface.

If your line of reasoning has you thinking that only an aggregate looks like aggregate then take into account that N-scale concrete (even old, weathered concrete) is nowhere near as rough as 1:1 scale aggregate--even smooth plaster. Styrene is much easier to work with and with the right color treatment looks more like concrete than any other building material.

[DKS]

Wow, you guys pretty much nailed my sediments.

 

[cv_acr]

The center support is not installed for this shot.

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.

[cv_acr]

Have not seen an all-concrete curved bridge... at least one that sharply curved.

In complicated highway interchanges, with ramps between two major freeways, I have, but agreed, no where near that sharp, and not on a minor 2-lane road.

[DKS]

In complicated highway interchanges, with ramps between two major freeways, I have...

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.

With the GSP less than a mile away--which is being widened as I write this--I live near a virtual sea of these:

...and not on a minor 2-lane road.

Indeed, I've never seen a curved bridge anywhere but a major multilane highway.