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Quick Bridges
- Thread starter unclesyd
- Start date
I've seen them used a few times and there are always questions as to what fatigue loads they have been subjected to. "Built like tanks" is a bit inaccurate as well. I have seen people wanting to haul Volvo rock trucks across railcar bridges with 2' deep spines and 60'spans. They can work, but they are not without issues of their own.
It's not new but novel and again brings up issues such as material properties, how to determine, etc. Nice for the odd bridge on a property with a small creek but not so much for the County or City engineer who has to answer to the people.
Regards,
Qshake
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Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
MiketheEngineer
Structural
I too have seen it done and actually did it once. Just for pedestrian traffic on a farm. Turned out nice.
Also have seen 18 wheeler trailers, sea going cargo boxes, etc used for similar purposes.
Also have seen 18 wheeler trailers, sea going cargo boxes, etc used for similar purposes.
I have attached a load testing and rating for a four-span bridge made of railcars. It does a thorough job of showing the effects span length and condition can have on different ratings (HS20, etc.).
Also attached is a Transportation Research Board report on Iowa counties adopting flatcars in low-volume roads as cost-effective solutions.
Also attached is a Transportation Research Board report on Iowa counties adopting flatcars in low-volume roads as cost-effective solutions.
Attachment didn't make it.
Non-engineer seems to be talking out his nether orifice in this article. "Flatcars come the railroad with . . . normal load ratings ranging from 140,000 to 180,000 pounds." A uniform floor load is what the ARRA used to rate these cars. This DOES NOT translate directly to three point-loads of anywhere near that total. Semi's have only three bearing points: Front axle [usually loaded to 12,000# max], 'Driver' tandem axles, and Trailer tandem axles.
And in pulp-wood country, a 120,000# log truck is not uncommon. So the two sets of tandem axles are exerting point-loads of about 54,000#'s each.
Somebody didn't do the math.
Non-engineer seems to be talking out his nether orifice in this article. "Flatcars come the railroad with . . . normal load ratings ranging from 140,000 to 180,000 pounds." A uniform floor load is what the ARRA used to rate these cars. This DOES NOT translate directly to three point-loads of anywhere near that total. Semi's have only three bearing points: Front axle [usually loaded to 12,000# max], 'Driver' tandem axles, and Trailer tandem axles.
And in pulp-wood country, a 120,000# log truck is not uncommon. So the two sets of tandem axles are exerting point-loads of about 54,000#'s each.
Somebody didn't do the math.
Duwe6, the 120 kip truck is a permit load vehicle. It cannot legally drive the roads without a permit.
The HS20 that Conjo talks about is the design vehicle loading for bridges. Well, the HS20 is the past bridge design vehicle now it is HL93
Furthermore, the HS20 does not actually represent ANY truck on the road. What it does represent is a bounding loading condition for multiple types of truck configurations.
The HS20 that Conjo talks about is the design vehicle loading for bridges. Well, the HS20 is the past bridge design vehicle now it is HL93
Furthermore, the HS20 does not actually represent ANY truck on the road. What it does represent is a bounding loading condition for multiple types of truck configurations.
tumbleleaves
Structural
A few observations:
1) People like them--because people like railroads.
2) They can make decent driveway bridges.
3) They are difficult to paint.
4) They are difficult to rate and often load restricted.
5) Many have wood decks that need replacement every so many years.
6) The railroad company "used" them--the railroads decided they were spent or obsolete.
Probably not the best choice for a public road. They are a novelty.
1) People like them--because people like railroads.
2) They can make decent driveway bridges.
3) They are difficult to paint.
4) They are difficult to rate and often load restricted.
5) Many have wood decks that need replacement every so many years.
6) The railroad company "used" them--the railroads decided they were spent or obsolete.
Probably not the best choice for a public road. They are a novelty.
tumbleleaves
Structural
Does anyone have anything to share about lead paint and flatcar bridges? Time period it was/wasn't used? Are the flat-cars still being supplied potentially leaded? Stories...potential problems..?
I’ve never used a flat car body as a bridge structure yet, but I sure have designed and built a bunch of them over the last 40 years for various railroads and industries. I have seen and read about them being used for small bride structures in various states and counties, and if I could pick the railcar bodies I think it would be a great reuse. Obviously, we would have to bend the AASHTO Interstate highway bridge standards a bit to make this work. I think railroads still tend to start retiring those types of cars after about 40 years, for many reasons other than a completely depleted primary steel structure. Some flat car types, body construction types, will be more conducive to this reuse. The 40, 50 and 60' car bodies (general purpose flats) are the strongest and huskiest, the 90' cars are for TOFC (trailer on flat car, or containers) service, and thus have fairly low load ratings, and are quite flexible. And, certainly not all derailed cars would be acceptable for repair and reuse, but many are repaired and go back into service on the railroads.
I agree with Duwe6 (10 OCT11) that the guy in the article, from Frankin Corp., is talkin a bit loose and out of his butt, with considerably more engineering and load rating confidence (bravado) than his real knowledge should probably actually warrant. However, a uniform load over the full length of the car is only one of the load conditions which the AAR uses to rate and design cars like those; and is actually not the most critical loading from the shear and bending moment standpoint on the car body. For design, these live and dead loads are combined with either a 350k tension loading or a 1000k compression loading on the car body; and these worst combined stress conditions at each cross section location have a 1.8 load factor applied to them, and there must be a positive margin of safety w.r.t. yield or buckling. So, there is actually a fair strength or gravity load reserve in most cases when you eliminate the axial loading. Once I see the stenciled weights on the car, I can draw the shear and moment diags. to which the car was originally designed, and probably tell you what the Fy is for some of the material, if not the actual ASTM Gr. with some degree of confidence. Then we could run any set of axle loads over that deck, with whatever FoS we wished to apply and compare the shears and moments. I would like to see how they support the car body at their prefab abutments, and how they support the end of the car body out beyond the centerplate. Those will be critical areas in achieving a good design for concentrated axle loads. I dare-say my greatest concern might be a safe and conservative abutment, wing wall, and footing design and foundation conditions I can count on; they might be the greatest uncertainly, soil bearing, flooding and potential scour, etc.. Then the exact best decking design will also be influenced by the car body type, and getting the wheel loads to the primary structural members. My design might not be quite as cheap as Franklin Corp’s. design, but my insurer doesn’t like me flying by the seat of my pants, as they seem to be doing.
If Franklin Corp. will strip a car down at my direction and clean it up, maybe sand blast it, so I can inspect the car body and the welds, I would be fairly confident in rating it for a bridge. I’m not unmindful of fatigue life on these types of cars because I’ve spent a lot of years worrying about the subject. But, generally speaking the fatigue problems on railcars had to do with bad details and welding conditions, and they tended to show up fairly quickly in the life of a railcar model. They were relatively low cycle fatigue problems, not something you would start drawing an S-N curve for. So, an old railcar body without many cracks is probably a pretty good structure, but I am hard pressed to say exactly what life it has left at a given stress level. We don’t know its exact load history or mileage, but these general purpose flatcars didn’t spend a lot of time under max. loading conditions, and they were not light enough so empty travel (vibration) was a critical fatigue problem.
As for Qshake’s comments (18JUL11), once I knew the car number, I might be able to get a copy of the builder’s spec. to which the car was actually built, likely not in every case. This might req’r. a few beers, assuming I still knew someone at that company. It is the City and County engineer, used to designing and building to AASHTO stds., who seems to have the most trouble rating something like this, from what I’ve read. They are a different beast, (the flatcars, I mean, although...) and I would not likely consider them in high traffic situations, or where the public expects to see a pretty new bridge. As for Tumbleleaves’ question (8NOV11) about lead paint, maybe we should let the salesman in the article blast and paint, as he offers, then that problem is his, and not ours. Generally the customer had a favorite paint system and we complied. Picking the paint was not the important issue for me, that was above my pay grade as the Chief Engineer, so I don’t know if or when we stopped using lead based paints. But, there is still plenty of it out there, and I wonder if it were essentially left undisturbed at the bridge site, if you might not then be in compliance. I wouldn’t expect a lot of kids out there chewin on it. Does anyone know how to get in touch with CONEJO, I sure would like to see those reports he didn’t attach?
I agree with Duwe6 (10 OCT11) that the guy in the article, from Frankin Corp., is talkin a bit loose and out of his butt, with considerably more engineering and load rating confidence (bravado) than his real knowledge should probably actually warrant. However, a uniform load over the full length of the car is only one of the load conditions which the AAR uses to rate and design cars like those; and is actually not the most critical loading from the shear and bending moment standpoint on the car body. For design, these live and dead loads are combined with either a 350k tension loading or a 1000k compression loading on the car body; and these worst combined stress conditions at each cross section location have a 1.8 load factor applied to them, and there must be a positive margin of safety w.r.t. yield or buckling. So, there is actually a fair strength or gravity load reserve in most cases when you eliminate the axial loading. Once I see the stenciled weights on the car, I can draw the shear and moment diags. to which the car was originally designed, and probably tell you what the Fy is for some of the material, if not the actual ASTM Gr. with some degree of confidence. Then we could run any set of axle loads over that deck, with whatever FoS we wished to apply and compare the shears and moments. I would like to see how they support the car body at their prefab abutments, and how they support the end of the car body out beyond the centerplate. Those will be critical areas in achieving a good design for concentrated axle loads. I dare-say my greatest concern might be a safe and conservative abutment, wing wall, and footing design and foundation conditions I can count on; they might be the greatest uncertainly, soil bearing, flooding and potential scour, etc.. Then the exact best decking design will also be influenced by the car body type, and getting the wheel loads to the primary structural members. My design might not be quite as cheap as Franklin Corp’s. design, but my insurer doesn’t like me flying by the seat of my pants, as they seem to be doing.
If Franklin Corp. will strip a car down at my direction and clean it up, maybe sand blast it, so I can inspect the car body and the welds, I would be fairly confident in rating it for a bridge. I’m not unmindful of fatigue life on these types of cars because I’ve spent a lot of years worrying about the subject. But, generally speaking the fatigue problems on railcars had to do with bad details and welding conditions, and they tended to show up fairly quickly in the life of a railcar model. They were relatively low cycle fatigue problems, not something you would start drawing an S-N curve for. So, an old railcar body without many cracks is probably a pretty good structure, but I am hard pressed to say exactly what life it has left at a given stress level. We don’t know its exact load history or mileage, but these general purpose flatcars didn’t spend a lot of time under max. loading conditions, and they were not light enough so empty travel (vibration) was a critical fatigue problem.
As for Qshake’s comments (18JUL11), once I knew the car number, I might be able to get a copy of the builder’s spec. to which the car was actually built, likely not in every case. This might req’r. a few beers, assuming I still knew someone at that company. It is the City and County engineer, used to designing and building to AASHTO stds., who seems to have the most trouble rating something like this, from what I’ve read. They are a different beast, (the flatcars, I mean, although...) and I would not likely consider them in high traffic situations, or where the public expects to see a pretty new bridge. As for Tumbleleaves’ question (8NOV11) about lead paint, maybe we should let the salesman in the article blast and paint, as he offers, then that problem is his, and not ours. Generally the customer had a favorite paint system and we complied. Picking the paint was not the important issue for me, that was above my pay grade as the Chief Engineer, so I don’t know if or when we stopped using lead based paints. But, there is still plenty of it out there, and I wonder if it were essentially left undisturbed at the bridge site, if you might not then be in compliance. I wouldn’t expect a lot of kids out there chewin on it. Does anyone know how to get in touch with CONEJO, I sure would like to see those reports he didn’t attach?
tumbleleaves
Structural
My take differs from dhengr, and I will comment further since dhengr contributed. However, I'm done on this topic and this is it for me.
Lead paint is an important topic.
In my career I have been the engineer of record on flatcar bridge designs and inspections. The region I work in presently has I would guess about twenty of these in service. I inspected a multi-span flat-car bridge a couple months ago that if I remember correctly was constructed in the 1950's, and I believe the most current one in the region was done in the 1990's.
I have seen flatcar bridges fail to various degrees typically due to some heavy ag vehicles, where they were not sufficiently modified for point loading. My state DOT does not allow funding for flatcar bridges, and I don't believe FHWA does either?
My experience is that City and County engineers (that I have met) loved flatcar bridges, that's why there are so many of them, and that FHWA and the state DOT put the breaks on: Because they are in nearly every instance not a good type selection for a public road, public bridges are about reliable long-term service with little maintenance.
My understanding of lead paint is that it is bad stuff, more so when it gets old and oxidized. I don't know how many times the dust from those old rusty, re-used junkers came down in my face (with who knows how much lead oxide).
Getting funding and/or environmental permits to remove or even modify a lead painted bridge is not a desirable task. Installing a lead-painted structure--nope.
My guess is that lead paint was likely phased out by the RRs in the 1970's? Or there about?????
Lead paint is an important topic.
In my career I have been the engineer of record on flatcar bridge designs and inspections. The region I work in presently has I would guess about twenty of these in service. I inspected a multi-span flat-car bridge a couple months ago that if I remember correctly was constructed in the 1950's, and I believe the most current one in the region was done in the 1990's.
I have seen flatcar bridges fail to various degrees typically due to some heavy ag vehicles, where they were not sufficiently modified for point loading. My state DOT does not allow funding for flatcar bridges, and I don't believe FHWA does either?
My experience is that City and County engineers (that I have met) loved flatcar bridges, that's why there are so many of them, and that FHWA and the state DOT put the breaks on: Because they are in nearly every instance not a good type selection for a public road, public bridges are about reliable long-term service with little maintenance.
My understanding of lead paint is that it is bad stuff, more so when it gets old and oxidized. I don't know how many times the dust from those old rusty, re-used junkers came down in my face (with who knows how much lead oxide).
Getting funding and/or environmental permits to remove or even modify a lead painted bridge is not a desirable task. Installing a lead-painted structure--nope.
My guess is that lead paint was likely phased out by the RRs in the 1970's? Or there about?????
tumbleleaves, I HIGHLY doubt that railroads had phased out lead paint by the 1970s - it is still an unparalleled corrosion inhibitor. For comparison: While it started phasing out long before then, lead paint was only removed from TxDOT specs in 1991. With some practice, you can often spot lead primers in the field pretty readily. Orangey-red is the most common, but you can also find darker red, green and blue colored lead primers. I most frequently see the orangey-red, followed by green (green was the "low lead" primer replacement for the orangey "red lead" primers. Green typically has the bonus of added chromium.
Tumbleleaves:
I really wish you wouldn’t quit on me. If you’ve been the EOR on the design and construction of a number of these bridges and have done inspections on other’s bridges, you have much more experience in using these flatcar bodies for bridges than I do. I’m not a bridge designer or engineer, my last serious bridge engineering was back in about 1965, but this idea intrigues me when I see these articles. All of my relevant experience has been in designing and building flatcars since about 1972, and in rebuilding them after some sort of damage. My interest is reinvigorated each time I see a new article on the subject, as was the case when I ran across this thread, since I don’t frequent the bridge forums very often. I sure would like to learn from you and pick your brain a bit. You can reach me at rwhai atcomcastdotnet, if you care to do so. I don’t know if the idea of using flatcar bodies for small bridges is good or bad, but would like to know more about your experiences. How did you get involved in these projects? Are you in private practice or do you work for some public agency and where are you located? I’m fascinated by the subject, but not expecting you to waste much of your time on a matter that turns you off.
I certainly was not making light of the lead paint issue, as I do think it is potentially a serious one. I don’t know when we last used lead paint on a car body. I thought that if you left it undisturbed, or encapsulated it, you were generally o.k. and in compliance. I did offer another option, only partly tongue-in-cheek, since the guy in the article offered, and that was to have him sand blast the car and repaint it, which would make that problem his, not ours. I would be inclined to agree with you that it was probably phased out in the 70's some time, but I’m not sure. In housing, I think the magic date is built after about 78, but you still better check.
I would be interested in knowing more about and understanding the types of failures you saw, so I could look at them from the car builders perspective. What types of flatcar bodies were used and their condition, and extent of repair before being put into bridge service. How and where were they supported at the abutments or on piers? Was some of the end of the car body cut off outboard of the body bolster/center plate area, or was that a failure area? What was the decking arrangement and make-up, because this would be strongly influenced by the type of body used or the types of vehicle loadings anticipated. What lengths and car cap’ys. were you using, do you happen to have car numbers? It would be interesting if you had any better insight into the economics on the matter, vs. the salesmen’s pitch in the article. Did you know how and where the flatcar bodies were obtained, did you have any choice in which car body and did you have any help in evaluating them and their strengths from someone who knows railcars, they certainly are a different animal?
I envision the critical stress areas on the car body structure being the transition area of the side sills and center sill just inboard of the RR trucks, and the end of the car outboard of the center plate and body bolster with an axle load at the max. cantilever. Also, half the weight of a vehicle out to close to the side sill could also be a problem on some car bodies and at some locations.
I really wish you wouldn’t quit on me. If you’ve been the EOR on the design and construction of a number of these bridges and have done inspections on other’s bridges, you have much more experience in using these flatcar bodies for bridges than I do. I’m not a bridge designer or engineer, my last serious bridge engineering was back in about 1965, but this idea intrigues me when I see these articles. All of my relevant experience has been in designing and building flatcars since about 1972, and in rebuilding them after some sort of damage. My interest is reinvigorated each time I see a new article on the subject, as was the case when I ran across this thread, since I don’t frequent the bridge forums very often. I sure would like to learn from you and pick your brain a bit. You can reach me at rwhai atcomcastdotnet, if you care to do so. I don’t know if the idea of using flatcar bodies for small bridges is good or bad, but would like to know more about your experiences. How did you get involved in these projects? Are you in private practice or do you work for some public agency and where are you located? I’m fascinated by the subject, but not expecting you to waste much of your time on a matter that turns you off.
I certainly was not making light of the lead paint issue, as I do think it is potentially a serious one. I don’t know when we last used lead paint on a car body. I thought that if you left it undisturbed, or encapsulated it, you were generally o.k. and in compliance. I did offer another option, only partly tongue-in-cheek, since the guy in the article offered, and that was to have him sand blast the car and repaint it, which would make that problem his, not ours. I would be inclined to agree with you that it was probably phased out in the 70's some time, but I’m not sure. In housing, I think the magic date is built after about 78, but you still better check.
I would be interested in knowing more about and understanding the types of failures you saw, so I could look at them from the car builders perspective. What types of flatcar bodies were used and their condition, and extent of repair before being put into bridge service. How and where were they supported at the abutments or on piers? Was some of the end of the car body cut off outboard of the body bolster/center plate area, or was that a failure area? What was the decking arrangement and make-up, because this would be strongly influenced by the type of body used or the types of vehicle loadings anticipated. What lengths and car cap’ys. were you using, do you happen to have car numbers? It would be interesting if you had any better insight into the economics on the matter, vs. the salesmen’s pitch in the article. Did you know how and where the flatcar bodies were obtained, did you have any choice in which car body and did you have any help in evaluating them and their strengths from someone who knows railcars, they certainly are a different animal?
I envision the critical stress areas on the car body structure being the transition area of the side sills and center sill just inboard of the RR trucks, and the end of the car outboard of the center plate and body bolster with an axle load at the max. cantilever. Also, half the weight of a vehicle out to close to the side sill could also be a problem on some car bodies and at some locations.
dhengr - 1978 is probably sounding familiar to you because the Consumer Products Safety Commission banned lead for consumer products (toys, furniture, housepaint) in late 1977, and most Federal literature talks about checking any houses built before 1978. This had no effect whatsoever on industrial use of lead pigments for corrosion protection on steel, and not a huge effect on housepaint. Lead in housepaint (basic lead carbonate or "white lead") was already pretty well along in phaseout because titanium dioxide is a better white pigment, and became available after WWII. Lead for corrosion protection of steel (lead tetroxide or "red lead") is a different beast and was not really starting a phaseout for most industries in 1977. Heck, red lead in paint is still used today in the USA for corrosion protection in limited circumstances - quite limited. It is still used extensively overseas, particularly in Asia. About 10 years ago I was peripherally involved with a lead lawsuit for a brand new billion-dollar semisubmersible drilling rig which had been specified in the USA and built in Asia. The global paint manufacturer who supplied the specified paint had an Asian version using the same name and number as the US version (Call it Superpaint 80.)The specifier checked the US data sheets, and Superpaint 80 was lead-free. Unlike the US version, the Asian version actually supplied was full of lead pigment. Upon delivery, the new owners were quite... put off by the lead paint.
tumbleleaves
Structural
I'm no expert in flat-car bridges at all. Each one was different. I worked on some odd stuff in private practice. Honestly, I don't have anything more to contribute on the topic.
I was laid-off from my non-bridge job, at my new job I'm working with bridges again, but do very little design work now, lots of environmental issues like lead paint. I was aware of the orangey-red primer, but the blue and green are new to me, so I learned something.
The flat-car bridges I did came from this fellow:
One of the suppliers would likely be a good source of information, but what's the point unless you have a client that wants to put one in...
I was laid-off from my non-bridge job, at my new job I'm working with bridges again, but do very little design work now, lots of environmental issues like lead paint. I was aware of the orangey-red primer, but the blue and green are new to me, so I learned something.
The flat-car bridges I did came from this fellow:
One of the suppliers would likely be a good source of information, but what's the point unless you have a client that wants to put one in...
Thanks for the info. TomDOT and Tumbleleaves. I didn’t pay all that much attention to the paint we used on our railcars or other structures, as often as not the customer speced. the paint and paint system to match what their Mech. Dept. used on their RR or in their own maintenance shops. In the last 10-20 years I’ve run into the lead paint issue more in buildings and housing than on industrial equipment. What with all the commotion surrounding lead paint and the regulating agencies involved, I would think it wise to test the paint before making dust and chips out of it. And then to determine what to do with it on a case by case basis.
Skip Gibbs Co. seems to have done a lot of work with these bridges and pretty much puts the lie to the idea that they can’t be built to take a substantial loading, given some of their photos, etc. Obviously, you have to be careful in your design using these, but they do seem to have given it some thought as compared to the article which started this thread. The design and deck arrangement will vary and be dependant upon the car bodies used and the anticipated loadings. They claim to be using mostly 89' TOFC flats and the oldest of those cars, in that class, are only about 30-40 years old and while they will have had high mileage on them they were generally not abused the way a std. general service flatcar might have been, since they were basically in dedicated service. Their design and construction is also fairly consistent amongst all the large car builders. They were made to take a full tandem axle trailer load, two trailers/car, plus a substantial axial train loading, with a load factor of 1.8, and with a positive margin of safety against yield or buckling. I did some early (experimental, can we make it work) design, using the std. AAR design criteria, on that class of cars for various RR’s and could never bring them in light enough. The RR’s then went to the larger car builders, who forced the RR’s to reduce the loading requirements and design criteria if they wanted that light a car body. But, they are at least a fairly consistent group of cars to start a general bridge design concept around. General service flatcar are all over the place in terms of age, wear and tear, strength or cap’y., and their individual structural arrangement, so they would need case by case consideration. I’d still be interested in answers or comments on my questions in my earlier posts if anyone is so inclined.
Skip Gibbs Co. seems to have done a lot of work with these bridges and pretty much puts the lie to the idea that they can’t be built to take a substantial loading, given some of their photos, etc. Obviously, you have to be careful in your design using these, but they do seem to have given it some thought as compared to the article which started this thread. The design and deck arrangement will vary and be dependant upon the car bodies used and the anticipated loadings. They claim to be using mostly 89' TOFC flats and the oldest of those cars, in that class, are only about 30-40 years old and while they will have had high mileage on them they were generally not abused the way a std. general service flatcar might have been, since they were basically in dedicated service. Their design and construction is also fairly consistent amongst all the large car builders. They were made to take a full tandem axle trailer load, two trailers/car, plus a substantial axial train loading, with a load factor of 1.8, and with a positive margin of safety against yield or buckling. I did some early (experimental, can we make it work) design, using the std. AAR design criteria, on that class of cars for various RR’s and could never bring them in light enough. The RR’s then went to the larger car builders, who forced the RR’s to reduce the loading requirements and design criteria if they wanted that light a car body. But, they are at least a fairly consistent group of cars to start a general bridge design concept around. General service flatcar are all over the place in terms of age, wear and tear, strength or cap’y., and their individual structural arrangement, so they would need case by case consideration. I’d still be interested in answers or comments on my questions in my earlier posts if anyone is so inclined.
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