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旧 2009-09-15, 04:16 PM   #1
huangyhg
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huangyhg 向着好的方向发展
默认 railroad rail moi

railroad rail moi
i am engaged in an historical house remodel and addition in a western us mining town. builders 90 years ago used salvaged railroad rail as rebar in concrete retaining walls and also as structural beams. i would like to make an assessment of some existing structure and possibly add some railroad rail beams of my own in the addition.
it would be easiest for me and more understandable for my building inspector if i can find a table for section properties of rail instead of expressing the shape mathematically and integrating. i looked in my personal library and only find section properties for standard shapes such as i-beam, channel, tubing, and the like.
railroad engineers (the ones calculating tracks and bridges, not the train drivers) must have the appropriate reference sources. can anyone recommend a source?
check out our whitepaper library.
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):
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
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.
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