Instruction for Girder bridge construction

[Gobbler]

I've done a search but cannot find what I'm looking for.  Can anyone direct me to plans for building a metal (I think it's called a girder) bridge for use outdooors?  Do you actually build it from metal or can you use wood and paint to resemble metal? 

[ttrigg]

Gobbler:
Check back over the last couple of months, David ("FJ and G") posted a very good little article about building a girder bridge using smashed copper pipe.

[Ray Dunakin]

I think I still have a couple bridge construction pics posted on my site:

http://albums.photo.epson.com/j/AlbumIndex?u=3009006&a=32116967

I had to remove most of them due to space limitations, if you need more I can email them to you. I built my plate girder bridges out of 1/8" thick G10 fiberglass sheet, a very tough, rigid composite material. The angle-iron braces were made from styrene angles. I used dots of thick craft paint to represent rivets. The result is quite realistic.

[FJ and G]

Flattened copper plumbing pipe cut with heavy duty tinsnips after 2 sides separated with tinsnips; HO rails create the grid pattern. You can solder these or use epoxy or silicone to attach. Then take dremel and smooth it out

Use steel supports inside. I’ve used a steel stop sign post or angle steel from Home Depot or Lowe’s. That gives it structural integrity









these last photos also used HO rails but instead of copper, I used metal rail gutter material, cut to length on a large table saw with metal cutoff wheel. The operation is a bit dangerous and used gloves and full face mask and padding

 

incidentally, the castings are concrete (supports) using a rain gutter (vinyl) as a mold with rebar in the center and holding it into earth exactly like Marc H posted on last page of this month's GRR magazine. He experienced severe cracking in all of his. I have not as of yet. I'm wondering if it might be how the concrete is mixed or the type that caused the cracking in his vice the rusty rebar expansion he mentions. Of course he could be correct as I'm not expert at structures

 

 

here's construction photos for the 2nd type of bridge (non copper). Notice the stop sign ppost. Wood is sandwiched and bolted to the sides with recessed bolt hole. The metal sides are then nailed into the wood and silicon calked for added measure. The HO rails in this type of metal are not soldered as were the copper bridge. Instead, I used a combination of epoxy and silicone; they've been up 2 years now no problems

 

 

 this bridge will hold several people standing on it. The hound sometimes walks on it, balancing herself

 

 

 

[Ray Dunakin]

FJ and G wrote: "Incidentally, the castings are concrete (supports) using a rain gutter (vinyl) as a mold with rebar in the center and holding it into earth exactly like Marc H posted on last page of this month's GRR magazine. He experienced severe cracking in all of his. I have not as of yet. I'm wondering if it might be how the concrete is mixed or the type that caused the cracking in his vice the rusty rebar expansion he mentions."

I've been concerned about that too, ever since reading Marc's article. My bridge piers also have rebar. I'm not too worried about the simple piers that support my plate girder viaduct. The rebar on this is completely surrounded by concrete, with none of it extending into the soil. Also, if they ever did fail, it wouldn't be too difficult to replace them.

What I'm most worried about is my cast concrete viaduct. Not only does the rebar on this extend into the soil, there is also a crack in the top of the bridge which would permit moisture to reach the rebar inside the bridge itself. And of course, this structure would be a pain to replace. I may try to force some sort of glue or sealant into the crack to slow any potential damage. Other than that, all I can do is hope that our dry local climate and the arid nature of my desert landscape will at least minimize the problem.

[Anonymous]

I see Boss BB is barking orders

[Gobbler]

    Thanks for the responses.  They give me a lot to consider.  I, too, read the article about concrete and rebar.... just after I finished pouring footings and piers to support a poured bridge.  I did not use rebar but instead used the flat, pointed metal stakes (can't remember what they are called) that are used to support metal expansion joints in concrete.  I DID drive them into the ground though through the footing forms and at the proper angle on up the piers.  They turned out pretty good.  I hope they last.

    Question for Ray:  where does one buy the G10 fiberglass?

     Questions for FJ and G:  1)  What are the dimensions of your single span bridge?

    2)  I don't understand what you mean when you say the "wood is sandwiched and bolted to the sides".  I guess I need to go to Lowe's and look at a stop sign post to get a feel for it.  What type of wood?   And dimension? 

    Thanks for the help.  I really need it.
 

 

[Ray Dunakin]

Gobbler wrote: "where does one buy the G10 fiberglass?"

Composite materials are usually carried by plastics dealers, so check the yellow pages for you local plastics supplier. Here in San Diego they're listed under "Plastic Rods, Tubes, Sheets Etc. Supply Centers".

If you're lucky, they may have something useable in their cutoffs bin. This will generally be cheaper but you may still have to pay to get it cut to size. For instance, when I built the 44" long section of my viaduct, I found an 8" x 48" scrap in the cutoff bin and had them cut it lengthwise into two sections 4" wide. I then cut two 2" pieces off of each one, and used those for the cross sections.

BTW, you could probably do the same thing using sheetmetal, with brass angles soldered to it for the braces. I chose G10 because it's something I've had experience with, it doesn't rust, and is dimensionally stable (minimal heat expansion). Plus my soldering skills aren't that great.

[FJ and G]

Ray,

Rebar is used in commercial projects all the time as well as residential for sidewalks and stuff, as you are aware. I’m not sure that iron in contact with oxygen or water and breaking down to iron oxide would expand. Rather, I’d think the oxide would displace the iron. So I still don’t really see how cracks could form because of that.

Small, non structural cracks are easy to repair with vinyle patching cement or flexible crack filleer, made for exterior usage, sold in Home Depot.

I think faulty concrete has to do with the mixing process and how well it is cured. I believe it needs to be kept moist for several days. That’s why sidewalks are often covered with plastic.

But I’m not concrete expert so this might all be hogwash.

Goobber. Look closely at the photo and you will see the wood. There’s holes in the stop sign where bolts can go thru and be recessed into the wood. The wood is there to hold the outside metal and give the bridge a bit more width. Angle iron, as Ray and I mention, could  be used in place of a stop sign, which you can’t really buy conventiently unless you remove a stop sign from an intersection, something you might not wish to do.

I got mine at a dump. The end was twisted

The 2 spans are 8 feet and 6 feet

The gutter castings with rebar sticking in the ground are merely for show. The concrete supports that actually support the bridge are at the ends of the bridge (3) One at each end and one in the middle holding the 2 bridges.

The clamps in the photo are holding HO rail to the metal, while the silicone and epoxy are curing. In the copper bridge (short pictured at the beginning of the post, they’re soldered to the copper).


The wood in the sandwich is treated wood for one span and cedar for the other

 

Incidentally (and this is a bit confusing), the below photos of the bridge are at the beginnings of construction and DO NOT show the rain gutter castings in place for aesthetic purposes. Someone criticized my bridge for it looking too long without supports. that's why I added those later.

 

[FJ and G]

OK, I have been pondering this for a few minutes and have reached the following conclusion:

Marc's concrete support was not set deep enough into the ground to get below the frostline. Instead, he relied on the rebar to stick into the ground and support the bridge.

A combination of iron oxide rust and water osmosis up thru the rebar created a very small opening or hairline crack that became moist and expanded with freezing temps. This pattern was repeated several times and the crack became bigger.

 

Had the concrete gone below the surface a couple of feet (he's in Colorado), I believe this would not have occurred. Commercial bridge supports are far below the frostline.

 

Anyway, that's my theory 

[Anonymous]

OK, I have been pondering this for a few minutes and have reached the following conclusion:

Marc's concrete support was not set deep enough into the ground to get below the frostline. Instead, he relied on the rebar to stick into the ground and support the bridge.

A combination of iron oxide rust and water osmosis up thru the rebar created a very small opening or hairline crack that became moist and expanded with freezing temps. This pattern was repeated several times and the crack became bigger.

 

Had the concrete gone below the surface a couple of feet (he's in Colorado), I believe this would not have occurred. Commercial bridge supports are far below the frostline.

 

Anyway, that's my theory 

This can be correct.

My is remember we must not forget the steel and concrete contract and expand but when the steel on/in ground alone I am not sure because I never poured like that but David's theory makes since.

William

[Gobbler]

Great looking bridges!!  FJ&G, I see that you have one with ballast and one with the ties directly on a hard surface.  Which do you like better?  Also, what is the width of your bridges?

 Thanks, Ray, for that info on the fiberglass. 

 Wm.

[altterrain]

I did not see the original article that Marc did but I'll agree with the Dave's conclusions. Their are many factors that can influence the strength of concrete. How it is made is a primary one. If too much water is added initially or if water is added later on to slow down the setting process, that can greatly reduce its strength. As Dave mentioned, hastening of the curing process in a dry environment by not keeping it moist or wrapped (Colorado is typically pretty dry) will also influence. A bad batch of concrete, i.e. a too high salt content, can also affect its strength. Whether or not exposed rebar can also influence this is unknown to me, as rebar or any steel reinforcement is usually fully embedded.

-Brian 

[FJ and G]

Hi William,

 

No preference; just like to try different styles of bridges. I don't have my measurements with me as I'm at work now but the track is 32mm so you might be able to gauge the width based on that. 

[Gobbler]

32mm???   What's that in American measurements? 

[FJ and G]

i think it is about 1.25 inches (O gauge). But you can sandwish wood of any thickness to meet your requirements, as I assume your track to be 45 mm or G gauge.

One thing I failed to mention, is that the ties are glued down directly to the steel stopsign post with Gorilla Glue. Used weightlift plates to press the ties in place while it cured, wetting everything thoroughly. No ties have popped off after 2 years.

That idea was from a couple people on this forum, which I'd like to say a big THANKS!

[Gobbler]

10-4.  Mine is "G" scale.

[Anonymous]

Here is a bridge made from 6 concrete  chimminy blocks and it is holding up well in the winter.            

here is another one of my bridges that i made.    ben

      

 

 

[Gobbler]

Good looking bridges, Ben.  Gives me something else to consider. 

[Anonymous]

Gobbler

 I hope you enjoyed the pictures i sent direct to you , i hope they help you in some way.    Ben

[Gobbler]

Enjoyed the photos, Ben and they certainly give me several options that I had not considered.  They certainly will help me in my construction.  Thanks.   Wm.