I never paid too much attention to them until recently. I am talking about truss rods under "old-style" wooden passenger and freight railroad cars. I was wondering what is the purpose of truss rods. I am not around fellow model railroaders or railfans, and I do not belong to any model railroad club, so I couldn't ask anyone. I tried to figure out the purpose of truss rods for myself and the conclusion I came up with is: since "old-style" wooden railcars have them, the purpose of truss rods was to prevent the railcars from sagging in the middle by the use of turnbuckles in the center of the truss rods for tightening. Design engineers back then didn't design the underbody frames of railcars strong enough to support weight in the middle, so there was a tendency for the railcars body to sag in the middle, between the trucks. Truss rods were designed to prevent this.
This is what I concluded about truss rods. Am I right?
Reinforcement. They have the same purpose as I beams or channel beams do in more mdern equipment; or, the unitized body of automobiles do today. They give strength in the direction needed to support the load placed on the car.
NP 2626 "Northern Pacific, really terrific"
Northern Pacific Railway Historical Association: http://www.nprha.org/
The truss rods serve a similar purpose like that of the frame of a automobile. That is to keep the body from sagging and hold the structure of the car together.
Dr. Frankendiesel aka Scott Running BearSpace Mouse for president!15 year veteran fire fighterCollector of Apple //e'sRunning Bear EnterprisesHistory Channel Club life member.beatus homo qui invenit sapientiam
Hi Tractionnut
Actualy the engineers did design the frames strong enough you have to remember the limitations of the matierials they had avalable, basicaly wood and wrought iron
Steel was a new fangled matierial back at that time and quality control in steel was not good or reliable
Which is why truss rods where added they are a vital part of the car frame.
They kept passanger cars straight and freight cars bent
If the truss rods on the freight cars where properly adjusted,
the frame had a slight up wards bow that may not even have been easily visable the car straightend out when loaded.
If the truss rods where not there the freight car frame would just break in half when laoded.
The classic sway backed car beloved of some modellers is prety much a falicy you could not have loaded it without breaking it
And if a result of poor maintainance no amount of tension applied on the truss rods would fix it the only thing to do is burn it and recover the expencive iron work, and build a new freight car.
regards John
Truss rods are used to create a truss structure, just like a truss bridge. It enables longer cars to carry more weight while weighing less. The loaded truss will have the top member made of wood in compression (where wood is strongest) and the bottom member made of iron in tension (where a long slender piece of iron is strongest). You could build a car solely out of wood but the size, number and weight of the beams to do that would be prohibitive. By using a truss you can get a much lighter structure with a larger capacity.
When you study the construction of wood cars, you can see how clever the early car builders were.
Dave H. Painted side goes up. My website : wnbranch.com
dehusmanThe loaded truss will have the top member made of wood in compression (where wood is strongest) and the bottom member made of iron in tension (where a long slender piece of iron is strongest).
if you want to see a good demonstration of this principle, take a long peice of foam maybe a 1/2" x 3" x 2' and glue a piece of balsa sheeting on one side (3" x 2') and put packing tape with the glass fibers on the other side.
This makes the structure very stiff when trying to bend it in one direction (strecthing the tape) but very flimsy in the other direction. All the tension and compression is in the tape and balsa. The foam just holds them in place.
greg - Philadelphia & Reading / Reading
Short answer:
You're right.
Your right, truss rods were used to prevent sagging, and deformation. But it wasnt because of poor or bad design. When truss rods were used, steel hadnt been implemented yet in the frames, nor other make up of cars. Both freight and passenger. Wood was good but to keep a car from "bending" would mean a bigger frame. That added weight and a larger frame. Not doable.
Passenger cars - were longer than freight and thus would tend to sag under their own weight. Remember all the fancy shmancy ornate decorations that were used inside the cars. That and the ornate metals (like brasswork) did weigh alot. All that on a wooden frame, plus the endless pulling and pushing placed on the frame from use in a train would definately play havoc on the cars. Using steel trussrods essentially kept the frames from bowing.
Freight cars - carrying the burden of a young industrial america and were shorter than passenger cars, but carried alot more weight in some cases. Just loading them sometimes would cause the frame to sag. Again, truss rods were used to stiffen it. As we know freight trains were alot longer than passenger.... carrying many more cars. Thats alot of push and pull on a frame that was closer to the loco than the end cars. An older car with a worn out frame without truss rods, could and would crush with no problem.
You will note than when steel finally made it to cars, it was implemnted slowly. You will find many companies (like Ralstan for example) would take existing cars and "re-frame" them. Keeping the wooden bodies they would replace the wooden frames with steel. Thus the nomenclature in freight rosters that lists "wooden - steel underframe" or "wd.- s.u.".
As we know wooden framed cars were phased out in favor of steel underframes. And eventually, cars (both pass and freight) were made from steel. Thus eliminating the truss rod. It was a big thing to have all steel cars then. It improved handling AND, on a better note... improved safety.
Wooden cars didnt fare well in crashes which were more prominant back then. Steel passenger cars were hailed by railroads and the public alike. Steel frames allowed for more weight, longer trains. And we all know, bigger-better-faster was the name of the game in those days.
Hi everybody!!!
I want to thank every single one of you for your replies/comments on the "purpose of truss rods". I learned alot about why truss rods were so important during the bygone days of wooden passenger and freight railcars. You see, I collect a lot of Suydam brass HO scale model trains that represent the wooden passenger and freight cars of the Pacific Electric Ry, and all of them have truss rods. But, I never stop to think what the purpose of of these truss rods were for. It only dawned on me recently what truss rods were for. But, I did have some idea that they provided some kind of support for the wooden cars because of the word "truss" in truss rod.
The turnbuckles in the middle of the truss rods was another clue. What I didn't figure out was that the truss rods were so vital to the life of the railcars and the people that rode in them. But, I learned a lot from reading all of your replies/comments. And I appreciate everyone of you for partaking in this discussion.
I love the wooden cars from a bygone era. Steel cars may be safer and major improvement over wooden cars, but they were nowhere near as beautiful as wooden cars. That's why I am such a fan of the Pacific Electric Railway, and an avid collector of Suydam brass HO scale wood interurban and freight train models.
Note that some wood cars with truss rods were later upgraded with steel center sills and other structual members underneath the car. But the truss rods remained. This is particularly evident in non revenue cars like cabooses that lasted into the 1960s on some roads. Look at photos of New York Central wood cabooses and you'll see what I mean. This was evident with some wood freight cars but likely no longer in interchange service after the the steam era for other reasons like age, etc. Some older truss rod equipped passenger cars were rebuilt too but usually remained captive on a given road, particularly shortlines. However, I believe there were some pressed into service during WWII and head-end cars of this kind of genre were more common. It all makes fun and interesting modeling.
Victor A. Baird
www.erstwhilepublications.com
Hi again,
It's me again - I've been visiting this blog again and again because I find all of your replies and comments on the subject of truss rods interesting. I understand the purpose of truss rods much better now - especially after reading this blog a few more times. I find you all very knowledgeable on the subject. I love those old "turn of the century" wooden passenger and freight cars the same way we love classic automobiles. But, I never stopped long enough to wonder what the heck those truss rods were for. I know now, thanks to the input you've all added to this discussion.
I appreciate it.
TractionNut :-)