Railroad rail MOI 1

One thing I've noticed is that very old rails tend to be much smaller than modern rails, so you may not be able to find modern rail of the same size as the existing. (In a mining town, those rails might have come off some sort of mine railway or narrow gauge railway as well).

If you can't find the information online, you might contact mills handling these products- seems like the one in Pueblo, CO, does rails.

A few years ago in my previous job, we had an add-in package for AutoCAD that computed section properties, given an polyline drawing of the shape. It took some tweaking and hand checking, but it really came in handy a couple of times. I know there are a couple of commerical packages out there, but there may be a freebie or two to be found.

I would not use old rails in any design. These could have been loaded hundreds of cycles per train and fatigued thereby reducing the strength.

Additionally, as reinforcing in concrete, I'd be worried as well. As the rails are relatively smooth, the concrete would not develop it as tension steel, but they would rather act in unison, both deflecting equivalently, sharing the load in proportion to their properties.

As far as section properties, you can draw the section in AutoCad, convert it to a region, do the "massprop" command on it to find the centroid, move the region to the centroid, and do the "massprop" command again to get the moment of inertia and such. I have no idea what psi to use as allowable. Might be good to send a couple of sections off to a lab and have them determine Fy & Fu.

I found overall dimensions here (but no sectional properties):


Older rail used bolted splices, modern rail uses welded splices, and I don't know how properties might have varied to accommodate that change. Also, old used rail may have been worn and/or ground, so section properties may not match new.

My copy of the "Standard Handbook for Civil Engineers", 2nd Ed., Merritt has a table on page 19-33 that provides rail info including section modulus and detail dimensions.

Yes, the rails all over town have various sizes. The pieces in my project are 6 inches across the bottom flange (not dinky underground ore car rail).

Excellent point on the fatigue of the rails. I have seen pieces laying around here with brittle fracture of the flange, probably evidence of cyclical load to failure. For my construction, I am looking at supporting a loft area about 150 square feet residential space. I will use new rail and ridiculously overbuild it. I just want to be able to show the inspector HOW overbuilt it is.

The old railing is horizontally embedded, with the bottom exposed flush, in a concrete retaining wall. I was planning to assume no bonding existed between the rail and concrete. The rail is supporting a simple uniform load (the wall and soil behind it). I don't know what, if any, additional metal is in the wall. If other evidence from nearby properties is accurate, it seems the practice was to include square section rebar too. In any case, for this retaining wall, it has been loaded, stable, and uncracked for 90 years. I am not planning on disturbing it for my project. I just wanted to run some numbers on it for a sanity check.

I'll loook for a copy of Standard Handbook for Civil Engineers at the library and if that doesn't work, an add-in for my old version of AutoCAD.

Thanks to all for the input!

If you give us the all the dimensions of the rail, one of us can look up the value in the handbook for you.

Or if you want to use Autocad, you don't need any special add-on. Just draw the cross-section, use the "region" command and select the outline of the section, then use the "massprop" command and select the region. Autocad will give you the area, moment of inertia, radii of gyration, etc.

Just noticed that ChipB already gave instructions for using Autocad to find the section properties. Sorry for the repeat.

See "Carnegie Pocket Companion - 1923", free zipped .pdf download from my website
The information that you are looking for (area, moment of inertia, section modulus) is there, pages 74a and 74b.

SlideRuleEra has hooked you up!

I was going to suggest using a Bethlehem 171#/yard rail. Carnegie's 175 has similar section properties. I'm looking at a 5th edition steel manual. The newer manuals don't have Carnegie Steel listed. Chances are, if the rail is that old, it came from one of these two places.

Square reinforcing steel? Huh, that's a new one on me. I worked on one 100+ y/o structure where they place barbed wire in the suspended porch slab. It had held up well until a contractor decided to work on it.

ChipB - The large sizes of square bars were used up until about 1940, I have run across them often in existing structures.

As a matter of fact, the "strange" diameters of the following modern "round" bars was set so that they still have the exact same crossectional area as the old square bars they replaced:

#9 Area = 1.00 In^2 for 1" Square Bar
#10 Area = 1.27 In^2 for a 1 1/8" Square Bar
#11 Area = 1.56 In^2 for a 1 1/4" Square Bar
#14 Area = 2.25 In^2 for a 1 1/2" Square Bar
#18 Area = 4.00 In^2 for a 2" Square Bar

Thanks SRE!
Now I can go home as I have learned something new! ;-) And, it's time to go! Headed to AISC's seminar tomorrow on the 2005 Steel Manual. I'll soon be as die-hard on it as 271828! I'm just to used to going with what I know. Pobably should take the green book home and leave it.

Yeah, square. It has embossments in it to capture the concrete and its twisted. We also find leaf springs, axles, miner's drill rods and everything else you can imagine used as rebar (thankfully little of this foolishness in my project)

SlideRuleEra, Thanks for the download!

Gantrex is a company I've used for industrial crane rail and accessories. This site:


has a pdf brochure that has American standard rail technical information.



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

Wow, even better! Now I have enough information to make my own rails. Ha ha