Large Scale Central

A Bridge Build for the Little River R R

Modeling
#21

Bob Cope said:

Tom,

My note was more one of a ‘heads up’ rather than a full out warning. I am aware of the other ‘Volunteer’ that sells the bridges made of ABS. I also believe that the material he is using is considerably thicker (on the 1/8 to 1/4" range) than the material you are using. Quite possibly the trussed nature of your build will be sufficient to hold up, but then again …

As for temps, if memory is correct you are ‘on the plateau’ which sees a bit lower temps. Living in Kodak we several times in my tenure there saw temps right at or a bit over the century mark. The other consideration that many forget about is the solar heating from sunlight. East Tennessee has a relatively clear atmosphere, little smog, so solar heating is higher than other areas of the country. Consider how fast you can get a sunburn - that is solar heating. Another more direct example, I laid a piece of Aristo brass track outside on a late summer day. 85 degrees ambient temp turned into 145 degrees with the solar heating at the rail. Although I now live in the panhandle of Florida, that is still a good general reference of how much solar heat can be.

Silver would definitely be a better choice over black in my opinion … FWIW. Black would absolutely add to the heating effect of the sun, where the silver would likely reduce it. My intent was not to scare you into questioning you build, but rather to hopefully assist you in preserving a great build.

A thought just occurred to me. IF you have some acrylic available, you might cut a piece to fit on the inside of the truss if it starts to sag a bit in service. This would reinforce the structure and hopefully not detract from the overall appearance.

Bob C.

Hi Bob,

Thanks for the thoughtfulness in your email. I really appreciate all you seasoned veterans here. It is great to “mull” all these things over with you guys.

I am learning a lot about ABS now and that will help me with future modeling.

I like the idea of reinforcing the trusses if needed. Good Advice.

We do heat up pretty intently here in Middle Tennessee particularly in August. That is one reason I allowed for plenty of expansion and movement in my track work. So far no big disasters. Hopefully no problems with this big bridge this simmer and if there are I now Know how to correct them.

Thanks for the friendly “heads up.”

Tom

#22

Span number 1 is now painted in primer. It is looking more like a steel bridge and the shiny plastic is gone. The white spots are sun rays through the blinds…not defects in the paint or measles.

(http://i542.photobucket.com/albums/gg412/DrGrab/photo_zps84d26e7a.jpg)

Tom

#23

Doc

If it wasn’t mentioned might I recommend a heavy clear coat of Krylon UV protection

#24

Rooster just Rooster . said:

Doc

If it wasn’t mentioned might I recommend a heavy clear coat of Krylon UV protection

Very good point. I will be getting this when I pick up the final color for the bridge and some more primer for span #2.

Thanks. Tom

#25

Watching all this from the sidelines here, Doc, and liking the build. I do hope Bob’s warnings turn out to be unnecessary, or that his suggested fix turns out to be satisfactory. We certainly do have to take into account the experience of these guys around here, don’t we?

What you’ve done so far looks really fine!

On a slight tangent, by the way, I don’t think you’ll have to worry too much about track expansion as long as your line incorporates a curve every so often. The curves absorb much of the movement very neatly. It’s the long straight sections that give trouble, hence in the deserts of N. Africa, pipeline engineers build regular bends into those steel pipelines that run hundreds of miles across the surface. In these locales expansion and contraction takes place constantly ovewr every 24 hour period, as you can imagine.

If you’ve read me expounding on this subject elsewhere, my apologies…

#26

Thanks John. I did not know that there was a difference in expansion of curves and straight line track. Amazing what you can pick up here on this site.

Tom

#27

Tom,

It is not so much that curves expand differently from straights, but the the curve acts as a place to absorb the linear expansion. Consider that piping companies spend thousands of dollars putting expansion loops in long steam piping systems. Do a Google search for “steam pipe expansion loop”, there are some good example pictures. I wish I had taken some photos of the movement of the club layout last summer.

I have some commentary on track expansion on the Bachmann forum, see the link below:

http://www.bachmanntrains.com/home-usa/board/index.php/topic,23152.0.html

This may answer some of you questions about expansion.

Bob C.

#28

Bob Cope said:

Tom,

Be wary of the ABS outdoors in hot weather. ABS does not have the structural abilities of the acrylics. ABS is one of the materials used in vacuum forming for those complex shapes in airplane models because of its flowing characteristics when heated.

What you have may well work, but just a note to keep an eye on it so if it starts to sag you can find a means to reinforce it before it becomes a real issue.

ABS can also be joined with MEK if you are working is a well ventilated area. I once, in a past career, built industrial models of chemical plants using what is now only known as Plastruct. MEK is what we used due to it’s fast setting time, as this is solvent bond in stead of an adhesion bond.

Great start on that bridge. Seems in the back of my memory I have seen that bridge in my explorations of the Smokey Mountains while living in Kodak. Will you be weathering it? And to what degree?

Bob C.

Hi Bob,

I was the one who told Tom about the ABS bridges built by a man in Tenneesee. I have built 16 feet of arch bridges in ABS and 8 deck bridges of ABS to form 1/4 of a 90 inch radius curve. No problems (yet) in the Southern California heat in the middle of summer, some full sun, some partial. I have had them in place for about 2 years. A friend of mine in Gig Harbor, Washington has had three truss bridges on his layout for almost 9 years, also built of ABS. Not the same heat as California, but direct sunlight in 85+ degree weather.

Rick Marty has two very large arch bridges, on his layout near Redding, CA. Built by the same man and using ABS. Not the coolest place in the world during the middle of summer. So far, so good.

#29

Great build, of a cool prototype! The use of ABS is of special interest to me, as I have long-term plans to build a through-truss bridge on my layout, and will likely be using ABS. It’s good to know that others have not had problems due to heat, which has been my biggest concern. I still may add some square aluminum tubes under the deck for extra measure – I wouldn’t want to break the bridge while scrubbing the track.

#30

Tom Grabenstein said:

Thanks John. I did not know that there was a difference in expansion of curves and straight line track. Amazing what you can pick up here on this site.

Tom

It’s all going to expand and contract at the same rate, Tom. But if you have a curve at the end of a straight run, that will be be where the movement occurs. This movement within a curve will take the form of virtually invisible extended or reduced radius. This movement absorbs any tendency in the straight run to buckle or kink.

On the desert, a long straight run of pipeline will not be straight at all. The engineers incorporate regular “S” bends. To an innocent observer these bends must seem quite whimsical, since there is no obstacle in sight to require these bends.

The “S’s” get stretched a bit in the cool of the night as they are pulled tighter by contraction in the straight runs and in themselves, and they get squeezed a bit in the heat of the day by corresponding expansion. The straight sections thus lengthen and shorten harmlessly, without kinking or strain.

I didn’t go into detail yesterday because I know I’ve written this somewhere else around here and I didn’t want to bore you with it.

So now you know; as long as your railroad has curves and no long straight stretches, you won’t be troubled with the expansion problem.

And isn’t it good news, these other fellows’ experience with the ABS plastic? Life is good!

#31

Thanks John and Bob for the clarification on expanding metal in curves and straight lines. Very good explanation from you both.

I have 20’ diam curves all throughout the RR and very short straight sections. It is supposed to be nestled in the Smoky Mountains after all. It looks like I will luck up on the expansion issues. Probably why nothing has happened to the track the last two summers here in Tennessee.

I will be watching the ABS bridge VERY carefully this summer. I hope to have a full report come September.

Tom

#32

Hey Doc,

Will the track on your bridge be attached or will it float?

#33

With our desert heat I did not attach the track on any of my bridges.

In the summer I just check it before I run.

Last Spring I had to stop working on my track about 10 in the morning because the track got too hot!

#34

I use GMM catwalks on my ABS arch bridges. The catwalks are fastened to the bridge and the aluminum rail moves in the catwalk ties.

(http://freightsheds.largescalecentral.com/users/gary_armitstead/_forumfiles/bridge11res.jpg)

This photo was taken during July 2011. IIRC it was over a 100 that day. No handrails in place at this time. It had been in the sun and weather for about four months. This was just an experiment to see how it would last over time. I installed them around March of 2012. In it’s permanent configuration, there are four of these arch bridges together to form a 16 footer.

#35

Ric Golding said:

Hey Doc,

Will the track on your bridge be attached or will it float?

Hi Ric,

Sorry for the delays in getting back to you re: your question. I have been in Haiti doing some medical work and just got back.

I hope to allow for some movement and the the track will be loosely attached with wire ties. I will try to post pics when I get to that point in the build.

Tom

#36

Gary, that’s an awesome bridge!

#37

I was able to get a little more work done on the bridge over the Little River. I am trying to recreate this style of bridge.

(http://freightsheds.largescalecentral.com/users/grabnet/Bridge with curve.jpg)

(http://i542.photobucket.com/albums/gg412/DrGrab/Longarmbridge-2_zps0347165b.jpg)

After much thought I decided to paint the steel structure black as all the prototype pictures I could fine showed the steel members were black. I also decided to lightly weather the bridge as it was in the late 1920’s about 20 years after it was constructed.

(http://i542.photobucket.com/albums/gg412/DrGrab/DSC06731_zpsec6ed12f.jpg)

(http://i542.photobucket.com/albums/gg412/DrGrab/DSC06733_zps77532fb4.jpg)

I positioned the two 40 foot spans over Nelson’s Gap on the Little River using a very temporary center pier and temporary attachments at both ends. I was thrilled It was strong enough to hold the first train over the chasm.

(http://i542.photobucket.com/albums/gg412/DrGrab/DSC06747_zps4dfafadd.jpg)

(http://i542.photobucket.com/albums/gg412/DrGrab/DSC06745_zps57b3c330.jpg)

(http://i542.photobucket.com/albums/gg412/DrGrab/DSC06744_zps49f54b1e.jpg)

I think this picture looks a little like the prototype one above.

(http://i542.photobucket.com/albums/gg412/DrGrab/DSC06735_zpsf7dd3d2f.jpg)

Next step as the weather warms is to build a concrete or concrete like pier similar to those above in the prototype. Ideas and comments are welcomed as the Little River RR advances a few more feet.

Thanks for looking.
Doc Tom

#38

Nice work, that bridge looks great!

#39

Sweet! They look even better in place on the railroad. Nice job Tom!

#40

…(http://www.freethoughtnation.com/components/com_comment/joscomment/emoticons/funny/images/smile.png)…

Nice work Doc!