Author Topic: How do I ... build a concrete bridge?  (Read 2043 times)

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rickb773

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How do I ... build a concrete bridge?
« on: September 09, 2013, 12:41:00 PM »
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I am trying to replicate a sense of a scene of the Manayunk bridges across the Schuylkill Expressway in Philadelphia. The scene is so condensed that I am not attempting to duplicate the actual scene, just get a "sense" of the scene. The basic landforms are done and scenic-ed to a "good enough for the time being" state. (I am trying to get my whole "phase 3 construction" done to the point I can get operations started, so I am moving onto my Camden area for the time being.)

I am looking for input on how (when I get the time) I can construct a reasonable concrete bridge similar to those in Manayunk. It does not need to be detailed.

Restraints:
I am pushing 67 and my modeling skills have seriously deteriorated (so it has to be simple)
The arches need to be architecturally modified to get the trains and trucks to fit underneath.

Here's the target:


Here's the current state:



Mark Dance style paper bridges:   :)

Philip H

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Re: How do I ... build a concrete bridge?
« Reply #1 on: September 09, 2013, 12:51:12 PM »
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Rick,
You could lay that pattern over some foamcore or Gatorboard and cut enough layers to bond to thickness.  Under a good coat of concrete paint no one would ever know.
Philip H.
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johnhale

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Re: How do I ... build a concrete bridge?
« Reply #2 on: September 09, 2013, 01:02:19 PM »
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I agree. I would cut it out of flat material and laminate layers together. then paint the whole thing "aged concrete", weather, and be done.
John Hale
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Philip H

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Re: How do I ... build a concrete bridge?
« Reply #3 on: September 09, 2013, 01:07:25 PM »
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And it looks like you need to adjust that far left hand side arch for clearance. :facepalm:
Philip H.
Chief Everything Officer
Baton Rouge Southern RR - Mount Rainier Division.

"Yes there are somethings that are "off;" but hey, so what." ~ Wyatt

"I'm trying to have less cranial rectal inversion with this." - Ed K.

"There's more to MRR life than the Wheezy & Nowheresville." C855B

Alaska Railroader

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Re: How do I ... build a concrete bridge?
« Reply #4 on: September 09, 2013, 01:07:58 PM »
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I still have this bridge to finish.....

Pomperaugrr

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Re: How do I ... build a concrete bridge?
« Reply #5 on: September 09, 2013, 03:52:16 PM »
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I still have this bridge to finish.....


I still have that bridge to buy, once they are available.  I have a spot reserved for it. 

Eric

John

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Re: How do I ... build a concrete bridge?
« Reply #6 on: September 09, 2013, 03:54:05 PM »
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ask lordzox ...

Scottl

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Re: How do I ... build a concrete bridge?
« Reply #7 on: September 09, 2013, 04:09:21 PM »
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I'm not an engineer, but I know rivers and that would be a peculiar placement of the bridge with the arch at the bank and well below the land to the left of it.  Assuming you don't want to modify the landscape and road (which are both nicely finished), I suggest looking at some different arch geometries or alternative types of bridges.  I suspect in that case the prototype would use a combination of truss bridges to give clearance for the rails, road and to provide the span for the river.

Zox

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Re: How do I ... build a concrete bridge?
« Reply #8 on: September 09, 2013, 07:19:41 PM »
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For building this bridge:



I used a "sandwich"-style construction as suggested above, although mine was basically Styrofoam between two slices of MDF (and dimensional-lumber spacers inside the piers, and paper laminated over the joints between the MDF and Styrofoam):



The upper arches and all the surface details were made out of laminated styrene (and generous application of Squadron Green Putty to fill the gaps):







The bridge deck is plywood, and the rounded breakwaters at the foot of the piers were shaped from MDF with a router. About the only structural materials I didn't use at some point were steel and stone. :)

I'd say the general sandwich technique, with appliqued details, is a good path to follow. Just don't do like me and try to insert the upper arches after the bridge deck is permanently mounted... :)
Rob M., a.k.a. Zox
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rickb773

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Re: How do I ... build a concrete bridge?
« Reply #9 on: September 10, 2013, 10:27:21 AM »
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That is beautiful!

How did you cut the rounded tops of the interior arches?

JMaurer1

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Re: How do I ... build a concrete bridge?
« Reply #10 on: September 10, 2013, 11:49:50 AM »
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We have a member who built a similar bridge for one of our modules. He had the side pieces laser cut (like AK RR did) and sandwiched them then painted it with concrete colored paint. Looks great.
Sacramento Valley NTrak

Zox

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Re: How do I ... build a concrete bridge?
« Reply #11 on: September 10, 2013, 06:52:34 PM »
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That is beautiful!
Thanks!

Quote
How did you cut the rounded tops of the interior arches?

I used a drill to make the arches in the "skins" before cutting out the major curve:



(I did the same sort of thing to make the tiny arches at the top of the piers.)

I was fortunate in that on the prototype, the arched tops of the small arches are only in the outer layer of the bridge. The interiors are vertical walls, as can be seen here, although it's not obvious at a casual glance:



So I didn't have to put a curved top of the "inserts" that span from one side to another.

If you can get a similar close-up of the bridge you're modeling, you might want to see if they did the interior the same way; i.e. the small arches are essentially cosmetic appliques.
Rob M., a.k.a. Zox
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It is said a Shaolin chef can wok through walls...

dave n

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Re: How do I ... build a concrete bridge?
« Reply #12 on: September 12, 2013, 09:41:14 AM »
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Those are some fantastic looking bridges guys!  I'm a styrene guy - use it for all of my scratchbuilding.  Here's an option for arches, which I would think would work for a bridge or a building.  For arches for my Modesto depot, I ended up doing them like this:





I cut the arches out of .020 sheet styrene, then glued ribs to the rear and attached thin strips that I flexed to form the inner round walls (.015 I think, if I remember right I tried to use .010 and the proweld melted the strips too much and deformed them)  Here's the finished product:


sd75i

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Re: How do I ... build a concrete bridge?
« Reply #13 on: September 12, 2013, 11:33:03 PM »
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  How about NOV/DEC 2001 N Scale Railroading?  Nolfork Bridge.  http://www.nscalerailroadn.com/008/NSR008.html

towl1996

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Re: How do I ... build a concrete bridge?
« Reply #14 on: September 13, 2013, 10:43:15 AM »
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Not modeling related, but I used to live in Roxborough and often parked my car under that bridge while partying at the River Deck in the 90's. Ahhh, good times...! Looking forward to seeing how this turns out, I always liked looking at that bridge, it seemed so massive, classic PRR.
Never argue with idiots; they'll drag you down to their level, then beat you with experience.