attach rail to tressel bents

[newto gscale]

We are building a tressel and need some advice on how to attach the lgb track to the top of the bents that form the tressel. Any and all ideas welcome . Thanks

[ttrigg]

I'm cheating on my bridge.  When building the roadway, I spaced the wooden ties just far enough apart for the plastic LGB ties to fit down inside. That way I can just drop in the track.

[jhsimpson62]

I have never found a need to attach the track to the trestle bents. One of my trestles is 70 bents long. When it heats up a bit (as it will in the south) the track is able to flex at the curves, but comes back in line as it cools.

[ttrigg]

JH:

Before I ask you a question, I would like to define a few terms.  I spent over twenty years designing, building and teaching others how to build timber bridges. Your post has left me with some concerns.

I have never found a need to attach the track to the trestle bents. One of my trestles is 70 bents long.

The substructure of a timber trestle bridge consists of "bents", either "timber bents" or "pile bents", timber bents are composed of (from bottom to top) 1) timber footings, 2) timber sill, 3) timber posts, 4) transverse bracing (commonly called diagonal bracing along the face of one bent), 4) timber cap, and scabbing (reinforcing lumber on the outside of the cap/sill and posts). 5) Longitudinal bracing (diagonal bracing running from one bent to another.)  Pile bents do not have the footers and sill as the posts are driven into the ground.

The superstructure of a timber bridge has the following parts.  1) stringers (large dimensional lumber spanning the gap between bents) 2) decking (timbers that run across the width of the bridge, (in the case of a RR bridge, these are the ties.) 3) tread way, (the actual wearing surface of the bridge, commonly 2x6 or 2x8 laid lengthwise on the bridge for vehicle wheels to roll on (in a RR bridge that would be the rails.)  Optional parts of the superstructure would be railings and walkways.

I take it that you have built the superstructure of your bridge (the stringers and decking/ties) and are attempting to attach the tails to wooden ties?  In my case the bridge is 27 feet long and has an "S" curve in it.  When I built the decking I spaced the wood decking material so that the plastic LGB ties would just drop in-between.  The rails rest directly on the timber decking but are not attached.  The plastic ties "float" between the deck while maintaining proper rail spacing and allow the rails to expand and contract.  I have noticed some expansion/contraction in the last few weeks, but do not believe it to be of any significance.

If this sounds like the ravings of an old lunatic, I apologize in advance as it was not meant that way.  I do not believe that you meant to say you are wanting to attach rails directly to your bents without any stringers or decking.  

If you are concerned about the rails lifting, you could "wire them down."  every 18 inches or so drill a hole through the lower rail flange and wire it to the stringer, but this would cause problems with rail expansion and might tear the bridge apart over time.  Better yet, run the wire over three or four deck timbers so the rail could "slide" on the wire.  In my case, to prevent "rail lift", about every foot I took my pneumatic nailer and shot in a brad from the underside of the plastic tie into the wood decking.

[runawaytrain726]

 this may be no help to you but this is the way my father and i built our bridge. first, we just get a long plank of wood and nail down the LGB track then stake it to the ground. then we added all the fine detail around it. but for curves, we got got a small plank off wood and cut the sides into angles so it'll fit into the next straight away and then finish it off with all the details of a lumber trestle. Again, this is what me and my father did on the Salazar Hillside Railroad & minning Co. And agaun this is just another way we did it and you really don't have to follow it.

                  There is no right or wrong in building a railroad. Just find the grove that works for you and go with it,

                         Steven!

 

[Anonymous]

OK, now I am totaly lost but what Trigger said is right, to float them. You also get away with with illision of the track being on the wood ties and not the plastic ones. Leave room for split jaws if your using them.

Trigg hit me with that 8lbs sledge please!

[Rex in Pinetop]

Okay let me see if I'm getting this right:

1)  Bents or posts are the upright/verticle supports (compression type loads)

2)  Stringers are the beams/trusses spanning between bents.  (tension type loads on lower members and compression type loads on upper members)

3)  Decking goes perpendicular to the trusses 

4)  Treads go perpendicular to decking

5)  Ties go perpendicular to treads followed finally by the rails

Did I get it close?

I understand the advantages of "float" with respect to expansion/contraction but what keeps the track (ties and rails) from shifting side-to-side on corners if it's not somehow attached or constrained by the treads?  I was planning on putting some brass pins through a few of the ties to keep things from crashing inside my helix.  Of course getting rid of the treads and ties and spiking the rails directly to the decking would solve that problem.

Rex

[ttrigg]

In an attempt to undo any confusion I may have created, here are a couple of pics of my bridge during construction, please ignore the mess on the ground. Notice the "S" curve crossing over the mainline on the ground level. Yes that string is the "grade line".


At the far right you can see the track floating in the bridge "decking".  After dropping in the LGB ties I glued on the "foot tread way" on each side, securing the ties to the stringers , vertically that is, they can still float in all four horizontal directions.  On the "S" curve, you will note that the plastic LGB ties sit directly on top of the stringers, no attachment at all.  I know it is going to flex with the weather and I am willing to let it do so freely.  I'm not going to try to fight that battle!

Yes this bridge has a rather steep grade, I'll talk about that later when the bridge is complete and rail service to Chateau de Vic begins.

[ttrigg]

Rex
1)  Bents or posts are the upright/verticle supports (compression type loads)
Perfection!
2)  Stringers are the beams/trusses spanning between bents.  (tension type loads on lower members and compression type loads on upper members)
Well Almost!  In my earlier post I made no reference to truss bridges.  Truss bridges introduce a whole new set of terms!  (see below)
3)  Decking goes perpendicular to the trusses
No!  Decking is perpendicular to the stringers.
4)  Treads go perpendicular to decking
Yes and No!  (Treads (or tread way) is used on a foot or rubber tire vehicle bridge, not on RR bridge, except on the side for foot traffic.)
5)  Ties go perpendicular to treads followed finally by the rails
Yes and No.  Putting tread way on a RR bridge is a waste of lumber.
Did I get it close?  

Pretty good, now lets see how many people I can confuse with this one!

In my previous post in this thread I have pictures on my bridge, the "timber bents" hold the superstructure up in the air, thus spanning the gap.  The superstructure of a timber trestle bridge (RR type) is just stringers and ties.  On the outside edges of mine, I gave the brakeman a place to walk along the train if needed.

A timber trestle bridge is a very sturdy bridge with one major draw back,  maximum span is in the neighborhood of 18 to 30 feet and not much more.  To span greater distances with timber we are now talking about "Truss Bridges"


Notice the much longer clear span of the truss bridge, also notice the triangular shapes that form the webbing in the truss.

A truss bridge (and there are many, many different types) has two trusses, one on each side.  The part that connects the two trusses at the bottom are called transoms.  The connecting parts at the top (IF used) are called "spreaders" and "cross bracing", these two parts carry none of the load, all they do is to keep the trusses from falling inwards on top of the rails.  Some truss bridges have the entire truss system underneath the stringers, ties and rails.  This allows you to build a longer span with smaller dimensional lumber.  If your RR has a hard time acquiring 18 inch by 24 inch by 50 foot dimensional lumber, Simply use 8"x12"x whatever, and build 4, 5 or 6 trusses for the bridge, put the transoms on top and you've got a "deck truss" bridge.
Thus:


Like I said, Transoms connect the two (or more) trusses and the stringers go directly on top of them.  Above that we would have the ties and rails.

Lets follow the "live load" for a bit.
The weight of the train is carried by the wheels, the wheels pass the load to the rails, the rails pass the load to the ties, the ties pass the load to the stringers, from here it can get messy, depending upon which bridge type we are talking about, but in general in a trestle bridge the stringer load is transferred to the bents and then on to the ground.  In a truss type bridge the load from the stringers is transferred to the transoms, then to the truss and then on to the abutments.

Just as a side note, the top bridge pictured here was constructed entirely from folded and glued manila file folders!  It supported a bowling ball rolled through it!

OK folks, now just how bad did I muck up the waters with this one?

[Rex in Pinetop]

Tom,

So in a non-truss type bridge stringers are parallel to the rails spanning between bents.  In a truss type bridge the spans between verticle supports are longer so trusses with a significant web carry the longer spans.  Transoms connect the trusses and the stringers on top of them are still parallel to the rails.  Ties go on top of stringers in both cases.  I guess you could say that transoms are like bents with the verticle supports replaced by the trusses.

Did I come closer?

Rex

[whiterab]

If you are really serious about building bridges and trestles there are two books I would recommend.

Model Railroad  Bridges & Trestles published by Kalmbach is a great book for designing and building your own bridges.  Great diagrams and pictures of just what this thread is discussing.

Now if you really want to get into the details of bridge building and really want accuracy, the Bridge and Trestle Handbook by Paul Mallery ( Carstens Publications) literally gets down to the nuts and bolts of bridge building for model railroaders.

Both of these books may be out of print but there is a good chance you can find them if you google them.  Understanding the basic structure of the different type of bridges makes them a lot easier to build.

[Rex in Pinetop]

Joe,

Thanks for the references.  I tried the Kalmbach site and they weren't there so they are probably out of print as you suggested.  I'm going to try my library and if that fails I'll go to ebay or google.

So now back to the original question - How to attach the track so the train doesn't push the track off the stringers.  I've heard

1)  Not a problem - Let them float  (I'm not real comfortable here because of the curves)

2)  Drill some holes in the rail and wire-thread them to the stringers  (Will take a fair amount of effort through stainless steel rails)

So what about just some lateral caulks on the ends of the ties spiked into the transoms?  That would keep the track centered on the stringers while allowing float.  Just an idea.  I haven't got my circular stringers down yet on the helix sections.

Rex

 

[ttrigg]

Tom,

Did I come closer?

Rex

<>

<>Perfection!

<>

[ttrigg]

So what about just some lateral caulks on the ends of the ties spiked into the transoms?  That would keep the track centered on the stringers while allowing float.  Just an idea.  I haven't got my circular stringers down yet on the helix sections.

Rex

Here is a thought, IF you are using "flex" track, because "flex" rails will slide on the plastic ties as it needs to move.  Cut the wood ties about 1/2" longer than the plastic ties.  Grab a redwood fence board, run it through your table saw in strips about 1/8~3/16 inch thick, soak them in water, bend as needed and attach to the outside end of the wooden ties.  This will "box in" the plastic ties to limit their lateral movement.  Then you might consider an expansion joint at both the upper and lower ends of the helix.  Just a thought!  If your helix is in full view this might not be too appealing to the eye.

[Rex in Pinetop]

My bents (lower level) and transoms (upper levels) are about 2 1/2" OC so I still need stringers for the track ties to rest on.  Right now I'm planning for 2 stringers 1/2" by 1/2" laminated (soaked, bent, pinned, and glued) to go beneath the rails.  The track is SS sectional 16.5' diameter connected with Split Jaw connectors.  I'm sure they will require some tweaking with a rail bender to keep the track dead center inside the helix which will surprise me if it comes out as uniform as I expect it to.  The top level inside width is 9 3/4"  so I don't have a whole lot of slop to work with.  If I let the track float on the stringers I can envision a heavy log train coming down a little faster than planned pushing the floating track off the stringers and crashing into the side of the trusses.  That wouldn't be pretty.  I have a lot of scrap 1/2" by 1/2" short sticks.  I could make some 1/2" by 1/2" by 3/4" beveled blocks that I could pin to some of the 560 transoms and bents and then use your suggested "1/8" wrap" pinned to the blocks to keep the track from sliding around.  I think that was what you were suggesting??  Would I need to do the inside too or just the outside?

Rex 

[ttrigg]

Rex;
I think you could skip the inside.  Runaway trains will push track to outside.  Expansion due to heat will push to outside.  I cannot think of anything that would push to the center.  I think you have the solution well in hand.

[imrnjr]

 Rex--- 

I'm putting  1/2x5/8 wooden rails outside both sides, (can't remember what they are called dagnabbit), which was prototypical for some of the NG lines.  They are not really guard rails since they don't sit on the ties, but I'm down this path  as both additional stringers for trestle stiffness, and as a way to lock the ever shifting rail on to the top of the trestle since its my first effort. 

I also put some blocking in between the stringers under the ties that I could run a black drywall screw into to hold the track during trestle assembly and in transport from the barn to the garden.    You can't  see the blocking and if you really wanted to you could leave the screws in place.

 

mark

[Rex in Pinetop]

Mark,

1/2" by 5/8" wouldn't bend very well for me so I went with 1/8" by 5/8".  Do you have pictures posted some place? 

Here are some photo's of one section of my helix as I try to figure out how to attach the track.  I put the outside "bumper" on outside of the stringers which are pinned to the transoms (upper level) and bents (lower level).  It looked lop-sided so I put an inside "bumper" on to form a "tray".  (I don't know what to call these parts either.)  All comments and suggestions are very welcome especially before I do to the rest of the 25 sections.

http://i178.photobucket.com/albums/w273/RANichols_2007/SRGRR087.jpg

http://i178.photobucket.com/albums/w273/RANichols_2007/SRGRR089.jpg

http://i178.photobucket.com/albums/w273/RANichols_2007/SRGRR091.jpg

http://i178.photobucket.com/albums/w273/RANichols_2007/SRGRR092.jpg

http://i178.photobucket.com/albums/w273/RANichols_2007/SRGRR093.jpg

Rex

 

[ttrigg]

Rex:

Looking good!!!!!

Where did you get the C-47? 

[kstrong]

Great looking woodwork there. I love the use of the nuts and bolts. Tedious, I'm sure, but visually well worth the effort. Looks like you've found a great technique for keeping the track in check, too. Most excellent.

Later,

K

[Rex in Pinetop]

K,

Thanks for the compliment on the woodwork, nuts & bolts, etc.  It took about an hour to assemble each of the 2' helix sections after precutting all the wood and prebuilding the trusses.  Lots of holes drilled and blind nuts threaded.  When it came down to the stringers, bumpers, and caulks I went with the much discussed nail gun and glue.  Boy did that go fast compared to the drilling and bolting.

This weekend I carry the whole works up to Pinetop for final assembly and track laying of the helix.  Each section slopes up a little over a 1/3rd of an inch so it will be transit time to prevent the roller coaster look.  I haven't converted my loco's yet so still won't be able to test the track although I'm sure I won't be able to resist the urge to let a car go free wheeling down just to check out the rail attachment scheme.

Rex

[rpc7271]

When I built my first (and so far only) trestle I put a third stringer in the middle of the bridge. (Trestles normally only have 2 stringers, one under each rail.) I then screwed my LGB track directly into that third stringer. It isn't prototypical at all but noone has ever noticed it or said anything. I live in Mesa, Az so sometime when you are down this way give me a call or drop an email and you can look at it. It will be on the convention layout tours next April.