Trestle question

Discussion in 'HO Scale Model Trains' started by ChadYelland, Nov 21, 2007.

  1. ChadYelland

    ChadYelland Member

    Hi, I have to build 3 or so relitively small trestles on my layout, the largest trestle in real life is about 500ft long and 100 ft high it was removed when i was about 12 and i cant find a good picture of it around here but i know they were pile trestles no cement foundations. The question i have is i read that 30ft is about the max height for pile trestles, would they have used 12x12 square post bents built on top of 12x12 pile bents for the high center section?? and would the piles be vertical with tapering square upper posts, seperated by a sill?
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  2. PWRR-2207

    PWRR-2207 Rogue Islander

    Check out "Model Railroad Bridges and Trestles" (Kalmbach Books), page 30. They show the use of 10" x 12" 'purlins' run parallel to the ground on 12" x 12" sills for heights greater than 30'. The posts remain square 12" x 12". Sash and sway supports stay 3" x 10". The number of posts increases as the width of the load area increases. Later on the book points out that the number of driven into the ground piles only changes from the standard 5 to a bent to 4 per bent for light load tracks regardless of the height of the bent.
  3. ChadYelland

    ChadYelland Member

    yes, i have the book, nowhere in it does it show a square timber section built ontop of a round pile section, except footings built on top of buried piles...
  4. PWRR-2207

    PWRR-2207 Rogue Islander

    Piles, posts, piers...

    Glad you have a copy as it makes this easier, kind of... Aye, the book seems to use the terms interchangeably. Almost all the photos in the book show square posts on anything over 16 feet high so how about we agree that piles go in the ground and are used to form a foundation while posts are square 12" x 12" timbers that go atop the foundation?

    Now to figure out what the dimensions are for your prototype... For your 100' height, you could us the girts shown in figure 3g on page 30 in a 10 section bent with 5 posts:

    Top of a bent:

    ...middle of bent removed to see dimensions at top and bottom of drawing...

    Base of a bent (dimensions based on 2" batting per foot of height per page 29):

    or you could calculate in the space required to build double sills for the purlins...
  5. nachoman

    nachoman Guest

    This page may help answer some of your questions:

    RGS Technical Page

    It's the Rio Grande Southern narrow gauge, and may not apply to your prototype. One thing I have learned is that narrow gauge people like to nitpick every single detail!

  6. ChadYelland

    ChadYelland Member

    I know what the book says thats why i came to ask you fellows, I found one picture of my brother and i standing on the fire barrel platform, sadly it only shows the top 1/3 of the bridge taken from the riverbank, shows 6 round posts for the bents of the center section and 4 square posts for the flanking bents. question still is how could they have round piles 90+ feet high, there has to be a sill partway up wouldnt you think? and can you have a section of perfectly vertical piles (say 6) then a sill and then battered round piles again on top of that?
  7. PWRR-2207

    PWRR-2207 Rogue Islander

    Reality is - If there is no sawmill nearby to re-saw the logs or the company that is building the trestle does not want to haul them to the site or pay to square them on-site, you will probably see round timbers used. So maybe the round ones were cut on-site and the square ones were hauled in or re-sawed on-site.

    Yes, there has to be a sill in the shoring to evenly distribute the weight across a larger area even if you have timber available that is longer. The piles are under a compression load and to resist the tension placed on the support, you need to distribute that tension. Like an i-beam, the sills and purlins would be the plate used to distribute that compression force outward and away from the weakest point in the support beam so it will not snap.

    Yes, that is called a "pier". It is typically used if there is significant water flow or soft ground to distribute the weight across a larger area for what you are shoring. That is why you see so many pilings under piers. If the depth is too great you will see ground tackle attachments to the shore and a floating pier. The other option developed years ago was the creation of caissons to reach a solid foundation for a pier or bridging structure to be built on.
  8. ChadYelland

    ChadYelland Member

    Nearly dry in the summer but a large amount of run off in the spring, it had big sheet steel ice breaker plates on the "piers" there has to be a picture of it somewhere around here, might have to set up the slide projector
  9. PWRR-2207

    PWRR-2207 Rogue Islander

    Good luck on the slide projector. I am down to one of those hand held viewers my Grandfather left me. Not even sure I could replace the bulb if needed...

    PS: I thought of another reason that the lengths and thicknesses of the timber would be limited when possible - they had to use block and tackle to hoist things into place. Given that they were using using scaffolding and the already built structure to rig booms off or attach the tackle, would you really want to find out how much weight your block and tackle can hold? :cry:

    Plus, as for square pieces - did you ever try to drill a hole in a round dowel without putting it in a vice or pinning it down? I would rather not be fighting with a cross member 30+ feet in the air because it keeps rolling off :wink:
  10. ChadYelland

    ChadYelland Member

    found 1picture so far, i have to scann the other. too bad it wasnt taken from farther back (can you tell i'm canadian by the picture)
  11. PWRR-2207

    PWRR-2207 Rogue Islander

    Cross braces

    I am looking forward to the other picture because it looks like they cross braced the bents atop the piers:


    Nothing in the book and after looking at 46 pages of pictures in Google, not sure there is anything on the web with the word "bridge", "bridge wood", or "bridge arch wood" out there that even looks close...
  12. chooch.42

    chooch.42 Member

    PWRR, Just a guess/observation; the angled members seem to be the same size and material as the verticles, much heavier than sway braces - could this be a simple form of TRUSS bridge as opposed to a classic bent-trestle ? As the piers support each truss unit, a lower tension member need not be as strong as an un-supported truss...? I ain't that kind of ENGINEER, just supposin'. Bob C.
  13. PWRR-2207

    PWRR-2207 Rogue Islander

    Aye or a combination of such architecture but since ChadYelland has been spot on with his recall, I am holding out for the other picture...
  14. ChadYelland

    ChadYelland Member

    here they are, sry there taken from the Slide projector, I have to thank my older brother and some highshool project i found in a box entitled Winter Scenes! Thats me and him next to the fire barrel. It looks like round piles for the approach bents (can they be that tall and a single length?) , and square for the center.
  15. doctorwayne

    doctorwayne Active Member

    Wow! :eek: That looks like something that only a modeller could dream up! Was this bridge being modified when the pictures were taken? The five bents near the centre have only four verticals each, whereas those at the left of the last photo all have six. Also, there seems to be a lot less sway bracing between those centre bents, and in your first photo, with the skaters, the piers almost look like they're forms for pouring concrete.

  16. ChadYelland

    ChadYelland Member

    The piers were never cemented, It was to protect the piles from Ice and debris damage during spring flood. When i remember it they were covered in sheet metal not just lumber. One end or part of the bridge was burnt at some point by a farmer, i have no idea how it looked before i assume it was rebuilt simular to how it was, Note in the first picture there are pile "stumps" sticking out of the ice, either from the original bridge or part of construction. I don't think i'll ever find a picture from 1924. I noticed how thick the caps are, allso two bents are closer to eacheother on the left side of the last picture, allso the center ones are battered much more then the others I dont know how the girts were placed to join them to the rest of the bridge. I assume that it took 6 piles to a bent because there driven directly into the clay, 4 was all that was nessisary for loading and stood on pile piers...
  17. Doc Holliday

    Doc Holliday Member

    I used round piles with a pile cap and a trestle on top for a lake crossing. Don't know if its prototypical or not. The first pic shows the structure and the second shows it in place.

    Attached Files:

  18. ChadYelland

    ChadYelland Member

  19. PWRR-2207

    PWRR-2207 Rogue Islander

    Engineering "Plan" versus "As-built"...

    Thank you for the pictures and the history. That explains a lot as to why things are dissimilar beyond "what the Designer planned, Purchasing supplied and the Construction Foreman actually built". I think the 30' length is a 'guideline' not a hard rule because the average US wooden telephone pole is either 30', 60' or 90' tall. So it is conceivable that they used 45' to 60' poles in the middle section. It is also possible that a larger sawmill could have a layout able to re-saw timbers that length rather than segment incoming timbers prior to re-sawing and that would produce some long square pieces for them to use.

    PS: Those posts near the piers could also be anchor points for rigging block and tackle...
  20. wpyr

    wpyr Member

    looks good

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