Just wondering why 20 ft containers are not stacked like 40 ft ones on trains in well cars?
One word: stability.It isn't hard to figure that two empty 20-foot containers would weigh more than one empty 40-footer. And their size doesn't necessarily mean that their loads are lighter. If you're lucky enough to see a semi truck with one 20-foot container, don't be surprised to see three tandem axles on the chassis--it's too heavy for the standard two axles.If the lower level of the stack car well contains two 20-foot containers, it's possible for a 40-foot box (or larger) to be loaded on top of it, and the inter-box connnectors will work with the outer ends of the 20-footers. However, if you were to put a 40-foot box on the bottom, and attempt to put two 20-footers on top, you'd only be able to use two IBCs on each of the 20-footers, causing the two inside corners to be free of tiedowns, hence unstable--and because of the weight difference, the load would likely be top-heavy.Now, if you were to have two 20-footers on the bottom, and try to put two more 20-footers above them, you'd have enough IBCs to make the load more secure in each to the stacked pairs. But by that time you've probably exceeded the gross rail load of the well, so that's a no-go, too.I hope this all makes sense.
Carl
Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)
CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)
CShaveRROne word: stability. It isn't hard to figure that two empty 20-foot containers would weigh more than one empty 40-footer. And their size doesn't necessarily mean that their loads are lighter. If you're lucky enough to see a semi truck with one 20-foot container, don't be surprised to see three tandem axles on the chassis--it's too heavy for the standard two axles.If the lower level of the stack car well contains two 20-foot containers, it's possible for a 40-foot box (or larger) to be loaded on top of it, and the inter-box connnectors will work with the outer ends of the 20-footers. However, if you were to put a 40-foot box on the bottom, and attempt to put two 20-footers on top, you'd only be able to use two IBCs on each of the 20-footers, causing the two inside corners to be free of tiedowns, hence unstable--and because of the weight difference, the load would likely be top-heavy.Now, if you were to have two 20-footers on the bottom, and try to put two more 20-footers above them, you'd have enough IBCs to make the load more secure in each to the stacked pairs. But by that time you've probably exceeded the gross rail load of the well, so that's a no-go, too.I hope this all makes sense.
It isn't hard to figure that two empty 20-foot containers would weigh more than one empty 40-footer. And their size doesn't necessarily mean that their loads are lighter. If you're lucky enough to see a semi truck with one 20-foot container, don't be surprised to see three tandem axles on the chassis--it's too heavy for the standard two axles.If the lower level of the stack car well contains two 20-foot containers, it's possible for a 40-foot box (or larger) to be loaded on top of it, and the inter-box connnectors will work with the outer ends of the 20-footers. However, if you were to put a 40-foot box on the bottom, and attempt to put two 20-footers on top, you'd only be able to use two IBCs on each of the 20-footers, causing the two inside corners to be free of tiedowns, hence unstable--and because of the weight difference, the load would likely be top-heavy.Now, if you were to have two 20-footers on the bottom, and try to put two more 20-footers above them, you'd have enough IBCs to make the load more secure in each to the stacked pairs. But by that time you've probably exceeded the gross rail load of the well, so that's a no-go, too.I hope this all makes sense.
One thing to remember about containers be they 20 foot, 40 foot, 48 foot or 53 foot. The ALL have nominally the same load limits for weight.
Intermodal cars are configured for two 20 foot containers on the bottom level with corner locks for all 4 corners of each 20 footer. The 2nd level containers being 40 foot, 48 foot or 53 foot all have the main securement posts set at the 40 foot distance. There are no securement posts built into the longer containers that would facilitate putting a 20 foot container on their top.
I suspect that putting four 20 foot containers together on a intermodal footprint - MIGHT - set up a 'unattenuated' harmonic rocking couple between the two pair of 20 footer that COULD damage the intermodal car. I am not a engineer (mechanical or railroad) and am just spitballing the conjecture of the rocking couple.
Never too old to have a happy childhood!
TEBU's and IBC's ..... oh my!
Some years ago on CSX's Jax, FL ramp, a side loader operator tried one night to lift two 20 FT containers out of the bottom of one of those older Sealand well cars at the same time (darwin award), as soon as the containers cleared the side loader arm snapped off not a good idea, 20 footers cannot be stacked on top, 40-45-53 footers are stacked on top of 2-20's depending on the type of well car, I also remember TTX had once had some well cars that 4 20 ft containers were loaded on it, I believe the cars were used on the Chicago-LA UPS transcon route, the well cars were in Jacksonville but empty, guess that idea wasn't great either.
It is also standard practice in the container industry that you cannot stack a 20-foot container on a 40-foot container, as the weight supports are in the corners or ends only and not in the middle of a 40-foot container.
All the double stack well cars that I have loaded have 4 nubs (for lack of the proper name) in the bottom of the car. They are spaced for 40' container posts. There are non in the middle. 40' and larger containers set on all 4 nubs, 20' containers set on 2 nubs. If 20' containers were stacked the inner end of the container could shift slightly side to side, not a good thing. You are not supposed to put just 1 20' container in a well car, should be 2.
Where the nub is there is a stop piece on the outside of the nub that would keep the container from riding up and over the nub do to a hard stop or start. So if a single 20' container was loaded in a well car it would be held in place if the hard stop was in the direction of the end it was on, but if in the other direction it could ride up and over the nub and be free to slide back and forth in the car after that.
Back in the mid-90's, BN and UPS invested in 28' cans that would be directly stacked in 56' well cars or top-loaded using a conversion rack. The cans had additional corner castings either 8' from the nose (UPS) or the tail (BN) to be compatible with the 20' standard. The well cars are still in service, and so are at least some of the cans. Look closely next time you see a UPS pup - it may actually be a container permanently fastened to a chassis. Here's a site that has some post-stack pics: http://www.matts-place.com/intermodal/part3/28foot.htm
I work at a ramp & the main reason that 2 20ft containers aren't stacked is that there areno walkways to the center of the car.It's against all safety protocals to walk on any part of a car without proper walkways.The weight is only a factor with loads,many boxes are empty.In the NS SIMS program,it will not allow a car to be overloaded.(I don't know about anyone else's programs).Many cars setup to hold twenties will have "nubs" in the center of the well. The outside of the car will be marked for 20's or no 20's.I haven't yet seen a car provided with more than 4 IBC's.Those Cars to hold 4 28ft boxes were special 56 foot cars.The origional user was BNSF & they came with a special rack that held the top boxes to the bottom.By the late 90's they were out of that service & were treatedas stand-alone cars for 20's to 53's.
Those 28' containers UPS tried were a missed opportunity, I think someone didn't quite know what to do with them or how to market them properly. UPS could've converted their entire fleet to containers and other LTL carriers could've taken advantage of stack service as well. OF course it would've taken a change in railroad thinking to want to take on additional business, and as we've all seen none of the U.S. class ones appear to be interested in growing business.
There's also another factor and that is the weight, I know for a fact that at least one major shipper of 20' containers overloads them on a consistent basis, which is why they located all of their distribution centers a stones throw from intermodal yards, so as to not run afoul of weight law restrictions. They always double stacked their pallets of canned pineapple, none of which came from Hawaii, but did come from the Phillipines and Thailand, and occassionally from Micronesia.
As I recall the 28' vantainer experiment, it was a bit like Flexi-Van in that it involved a considerable need for moving inconvenient hardware around if the lane loads didn't precisely balance. The 28s I remember were little more than Stoughton dry-van bodies - as I recall the upper castings were for lifting only, and you wouldn't want to stack anything heavy on top of them if in a 56' well car. If anyone is wondering what the 'conversion rack' looked like, it went over the top of a 40' or pair of 20' stackable containers (making them inaccessible until the rack was physically removed) with the 28s locked on top.
These would have been a nifty solution for those proposed high-speed Z trains that UPS experimented with (using Amtrak Genesis power to have locomotives 'fast enough') but once stack operations with overhead loaders or cranes became a standardized technology, there wasn't much point in oddballs needing special care restricted only to domestic land intermodal service.
Here is a picture of what was involved in the 'conversion rack', from one of the sites linked in this thread:
In my opinion, this could have been converted to work with 48' or longer ocean containers or equivalent, given a little care in placing the sled during terminal activity. But it still wouldn't have the flexibility either in full doublestack for rail, or in having full and inherent light-tare-weight roadgoing chassis available at all times as in TOFC.
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