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eTraxx
Fireman



Posted - 04/01/2011 :  8:46:17 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Just down from where the pump house will go there is a need for a bridge. The On30 track that serves the Hill Valley Coke Company Coking Ovens siding is owned by the Lugoff & Camden RR (I just HAD to get my line in. Ha) .. anyhoo .. since the purpose of a model railroad is to have trains that run on it .. a pump house or coke ovens are of little use without a rail connection. To that end I figured I needed to get my trains running .. and for that I need to be able to cross my river.

At one time I had intended to model HOn30 .. but .. at some point I was seduced by the Dark Side. During that pre-HOn30 time I had got my clamy hands on a Central Valley Model Works #1903 72 Plate Girder Bridge (single track).



I was happy with the kit and when I went over to On30 I decided I wanted to take the bridge with me. It has great details and would be a shame to not make use of it.



This represents a 72' Single Track Plate Girder Bridge in HO scale. This is 36 feet 3 inches in O scale. Obviously, the tie assembly (8) will have to go but perhaps not so obvious at first glance is that the cross girders and rail bearers (6) will also be tossed. I will build this up from plastic structural shapes.

The main side girders then will be what is actually used. Using HO scale engineering structures in O scale effectively reduces everything by 1/2 (approximately). That's not precisely true since you can reduce the gauge of a locomotive but people remain the same. True, you can reduce cab height and width but generally one of the neat things about narrow gauge locomotives is that the cab appears larger in comparison to the running gear then on a standard gauge locomotive. Let's just say that a 3 foot gauge locomotive is about 2/3 the size of it's standard gauge cousin. If you divide standard gauge into three foot gauge (36"/56-1/2") you get 0.637 which is pretty darn close to 2/3. For On30 that would be 30"/56.5" or a ratio of 0.53

Now .. don't get me wrong .. I know that you can't simply reduce a standard gauge locomotive by .53 .. the cab, walkways, ladders and all of that are still 'people sized' .. but the locomotives that I will be using are small anyway like the Davenport, they will be more industrial size engines. The point being after all of that long winded noise is that I will be happy using the main girders in O scale.

Edited by - eTraxx on 04/13/2011 08:05:53 AM

Country: USA | Posts: 2959

eTraxx
Fireman



Posted - 04/01/2011 :  8:49:44 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Here's where the bridge will go. You can see, I have the track on either side and some crude beginnings of what will be bridge abutments.




Edited by - eTraxx on 04/13/2011 08:06:39 AM

Country: USA | Posts: 2959 Go to Top of Page

eTraxx
Fireman



Posted - 04/01/2011 :  9:01:43 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
I wasn't worried about finding appropriate sized structural members to replace the Cross Girders and Rail Bearers .. Evergreen styrene could supply that. What I needed to determine was the Cross Girder length .. aka the width of the bridge between the Main Girders.

I measured the CV Cross Girders .. at 2.230". Taking a quick look at the NMRA S-7 Clearances we find that for HO - centerline to extreme width is 1-1/32" or 0.03125". Doubling that we then get 2.0625" for maximum width. Hold on .. just a little more math ... (2.230" - 2.0625") / 2 = 0.08375". Ok .. ok. Getting nutz with the 'exact' math .. but hey .. having fun here. That means that the Central Valley Plate Girder bridge measures 0.168" wider then the NMRA clearance for HO. Cool. I simply need to find the NMRA clearance for On30 and add that 0.168".

Referring back to the NMRA S-7 Clearances we find that this dimension for On3/On30 is 3". Adding that 0.168" we end up with 3.168" for the width of the new Cross Girders.




Edited by - eTraxx on 04/13/2011 08:07:38 AM

Country: USA | Posts: 2959 Go to Top of Page

eTraxx
Fireman



Posted - 04/01/2011 :  9:03:46 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
.. a little math ..

The Cross Girders and Rail Bearers of this casting are 1/4" high. In HO that would represent an I-Beam 22" high. In O scale of course, it would be 12".

Just for fun. When you double the size of something .. H x W x L it cubes the volume. Looking at that another way .. if you had a steel cube measuring 1" x 1" x 1" it would equal 1 cu. in. .. if you double the dimensions so you get .. 2" x 2" x 2" the volume now is 8 cu. in. A narrow gauge locomotive is about 2/3 that of a standard gauge locomotive or 0.666~ .... therefore that same 1" sq. cube reduced to .666" x .666" x .666" would be 0.295 cu.in.

Round that to .3 .. so something 2/3 the size will weigh about 1/3. From the 'American Civil Engineer's handbook' we have a chart. An I-Beam 21" high weighing 100 lbs per foot has a Coefficient of strength of 1,766,100 (calculated load in pounds that will produce a stress of 16,000 lb per sq in on the extreme fiber when the span is 1 ft. By dividing this coefficient by the span in feet, the safe load uniformly distributed in pounds is found). Figuring 1/3 of that we get 588,111 COS. That equals to around a 15" high beam at 40lbs per foot. a 12" beam (that's what the CV beams work out to in O scale) would have a COS of about 500,000. Since in "my world" the locomotives that will be using this bridge will be on the light side .. even for narrow gauge, that 12" beam would probably be ok.

With that in mind I looked at what I have in my parts box as far as I-Beams. I have .. 3/16", 5/16" and 3/8" Evergreen I-Beams. Cool. The 3/16" I-Beam is too small as it would only be a 9" I-Beam. The 3/8" I-Beam would be a 18" beam. The 5/16" I-Beam would be a 15" beam. Shazam! That will work! Now, the Evergreen 5/16" I-Beam #278 has a flange width of .134" which equals 6-1/2". That is close to a 15" I-Beam running 85 lbs per foot and having a COS of 1,131,000 which means it will more then be sufficient for our bridge. Cool.



Country: USA | Posts: 2959 Go to Top of Page

eTraxx
Fireman



Posted - 04/01/2011 :  9:06:52 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Using the data collected in the prior section, here's the 'new' bridge I beams ..





With that I can print off a full-size plan of the new bridge structure. I will tape this to my work surface (12" sq marble tile) and use double-sided tape to build the structure directly on the print.




Edited by - eTraxx on 04/13/2011 08:08:26 AM

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visman48
Fireman



Posted - 04/01/2011 :  10:19:09 PM  Show Profile  Visit visman48's Homepage  Click to see visman48's MSN Messenger address  Reply with Quote
Ed,
Thanks for the info, I have some of these and will be using them someplace. Not sure I will have the same approach...details wise but I like where you are going...

Les



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eTraxx
Fireman



Posted - 04/02/2011 :  07:32:07 AM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
I had started on this and got as far as gluing up the bridge frame .. Cross Girders and Rail Bearers and realized that I had messed up.



I had made both using the 5/16" Evergreen I-Beam .. and that won't work. Here's why ..

This is the CV casting flipped over to look at the underside. To make the casting easier they have the Cross Girders and Rail Bearers the same height. The Lateral Bracing (X-Bracing) looks ok .. until you look closer. It actually passes through the Rail Bearers when it should clear that. I looked into it and the Rail Bearers are not as tall as the Cross Girders.



While browsing this morning and having coffee and pancakes w/sausage I sketched a little. I looked into it and a bridge like this, the Rail Bearers are not as tall as the Cross Girders. I decided to go with th 5/16" Evergreen I-Beam for the Cross Girders and 1/4" Evergreen I-Beam for the Rail Bearers. This leaves a 1/16" space between the bottoms of the two I-Beams .. which is perfect for 1/16" Evergreen Angle Iron.




Edited by - eTraxx on 12/25/2011 8:19:47 PM

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eTraxx
Fireman



Posted - 04/02/2011 :  3:06:09 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Have all the girders sliced, diced and sanded and ready to assembly the bridge frame.



I used my home made sanding tool .. called a 'Shooting Board' evidently/possibly. I'm calling this my prototype .. it works but having used it for a bit I am ready to make another .. better.




Edited by - eTraxx on 04/13/2011 08:09:31 AM

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eTraxx
Fireman



Posted - 04/03/2011 :  1:44:24 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Bridge frame glued up .. building X-Bracing




Edited by - eTraxx on 04/13/2011 08:10:01 AM

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eTraxx
Fireman



Posted - 04/04/2011 :  07:46:17 AM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
One more X-Brace to glue up. Each X-Brace is made up of paired .060" Angle glued to make a "T". The brackets I am adding actually do what they REALLY do .. and that's reinforcing the joints.




Edited by - eTraxx on 04/13/2011 08:10:29 AM

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eTraxx
Fireman



Posted - 04/04/2011 :  7:11:12 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Finished this part .. take a beer break and then attach to main girders




Edited by - eTraxx on 04/13/2011 08:10:58 AM

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sn3forme
Engine Wiper



Posted - 04/04/2011 :  9:07:04 PM  Show Profile  Reply with Quote

Very nice tutoral Ed,
I will need a few bridges on my layout
and I will learn plenty here. Just please,
tell me there will not be a math test
at the end of this thread!



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elwoodblues
Fireman

Premium Member


Posted - 04/05/2011 :  08:22:29 AM  Show Profile  Visit elwoodblues's Homepage  Send elwoodblues a Yahoo! Message  Reply with Quote
Ed,

OK, all that math is giving me a whopper of a headache.

I like the thought process you have put into designing the new bridge frame. You're going to have a great little bridge that won't look out of place with the equipment running on it when its completed.


Ron Newby
General Manager
Clearwater Valley Railway Co.
http://cvry.ca

Country: Canada | Posts: 6441 Go to Top of Page

eTraxx
Fireman



Posted - 04/05/2011 :  8:52:24 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Making some progress. Taking it slooowwwly .. trying to align everything which means glue a bit .. let that set up. I'm adding the triangular braces .. having to file to fit the larger cross girders but think they will work. One thing they do is to actually act like the full scale braces .. and brace the darn thing! :)



One thing though. Take a look at this photo. This is the stock bridge structure with the tie assembly. While in HO the ties overhang a bit .. 30" beyond the rail bearers. Seems to me that in 'real life' the ends would have been supported on something. These HO ties measure out at a little over 11' in length.



Narrow gauge ties run let's say 6-7' in length .. but what about the bridge ties? I'm guessing 8'? If so .. what the heck supports the ties on the outside?



Edited by - eTraxx on 04/13/2011 08:11:28 AM

Country: USA | Posts: 2959 Go to Top of Page

eTraxx
Fireman



Posted - 04/05/2011 :  9:15:44 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Well. In a book titled "Notes on track : construction and maintenance By Walter Mason Camp" pub 1903 I found a diagram showing that .. yepper .. the ties overhang. If I used 8' bridge ties .. that means they would overhang the rail bearers by only about 33" .. which is the same (pretty much) as the standard gage overhang.



Interesting book though. Found that at least! :)

Edit: On page 847 it says .. "The size of tie required for a bridge floor depends upon the manner in which the tie is supported. If the tie is supported by stringers directly under the rails (which mine does .. aka .. the rail bearers) or nearly so, it supports the rail without appreciable bending movement, and other then this its duty is merely to hold the rails in gage and in line. Under such requirements a tie of ordinary size is sufficient, and the common sizes are 6x8, 7x8 and 8x8 ins., the first and last mentioned being the most common."

Well. That pretty much answers that. 8' ties will fit with clearance between the triangular braces. 7' might be better. Will have to wait to I get to that part! :)



Edited by - eTraxx on 12/26/2011 07:47:03 AM

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eTraxx
Fireman



Posted - 04/06/2011 :  6:11:45 PM  Show Profile  Visit eTraxx's Homepage  Reply with Quote
Ok.

QUESTION TIME!!

The instructions that came with the Central Valley Plate Girder bridge are basically useless when getting to where you want to attach the bridge shoes.



I'm sorry. I could draw a better image with a pencil held between my toes.

Sheesh.

Here is a close-up of a couple of the shoes still on the sprue ..



My guess is that I have them oriented correctly in the photo with the longer 'bits' up top pointing in toward the center of the bridge.

Could use some help here! :)



Edited by - eTraxx on 04/13/2011 08:12:36 AM

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