Monthly Archive: February 2012

A Good Question Considering Shipping Container Structures

This question came in to me by e-mail considering shipping container structures.  It is from a graduate student that is doing research on the structural design and analysis of a shipping container building, and he is working on doing it by FEM (Finite Element Method).   Finite Element Method design is a very good way to model complex structures and lends itself well to computer analysis.  I’d like to share my answer with you all:

——– Original Message ——–
Subject: Dry Cargo Shipping Container Structural Integrity
From: “Shane xxxxxxxxxx
Date: Tue, February 21, 2012 2:13 am
To: georger@runkleconsulting.com

Dear Mr. Runkle,

I want to begin to thank you for taking the time for reading this email. I will try to keep short and clear.

I am a structural engineering graduate student at xxxxxxxxxx and I am involve in a multi-disciplinary team designing the next generation of innovative student housing at xxxxxx campus. The multi-disciplinary team has decided to design a high-performance sustainable green structure that will have a dome-mound of dirt as a green roof and the main structural system will be composed of repurposed shipping containers.

The reason why I am emailing you is that I was researching online about any structural analysis or finite-element analysis that has been done for dry cargo shipping container and came across your name at this website: (http://ronestudio.wordpress.com/2012/02/10/basic-container-design-structural-considerations/)

I wanted to kindly inquire if you know of any published information about the structural integrity of cutting walls and windows to dry cargo-shipping containers.

I have found several technical specification requirements from ISO that accounts for both static and dynamic loading but all are under the assumption that the load path is from the cargo floor>C-beam floor joist>Longitudinal C-beam>Corner fitting>Foundation (or the next lower shipping container column).

So far, roof-loading scenario of soil mound is 600lb/sq. ft. and ISO requires roof of shipping containers to handle 300lb/sq. ft. We are looking to reduce load by using alternative fill material but are still concern about combining 20′ shipping containers and cutting entire wall out. I have found one case study of a cabin that you advise by replacing entire wall with two 6″x3″x1/4″x19′ steel box beams welded the entire length of the containers. I believe this cabin did not have loading scenario as much as we have.

With that said, I kindly ask if you could share any information you have regarding structural integrity of a shipping container used as housing. I will be performing a finite-element model of our final design and I wanted to see what information is out there before I begin. Again, thank you for your time and I look forward to hear back from you!

 

Kind Regards,

Shane xxxxxxx Graduate Student

==============================================================================

Shane,

There is no published information about container strength when they are cut up, and because there is a huge number of configurations, a prescriptive type of guidance would not work.  You have to break the container down into its constituent parts and model it based on the sections of the parts.  I use a 3d FEM program (Bentley RAM Elements) and I have put all the parts in as sections.  For the sides, I use thin steel shells.  You have the following parts in a container:

1.  Rear posts – these are roughly steel angles.  It’s fairly simple to calculate the moment of inertia of these, or draw them in AutoCAD and let it figure the modulus with the MASSPROP command.

2.  Front posts – these are fairly complex members made from two different size channel sections.  The moment of inertia can be found by drawing these in AutoCAD and using the MASSPROP command.

3.  Bottom Rails – these are C sections, again fairly easy to calculate section properties.

4.  Top Rails – these are steel tube sections

5.  Side corrugations – these can be modeled as cold formed hat sections.

6.  Top corrugations – again, can be modeled as cold formed hat sections.

To get specific information on containers in the form of drawings, check out this site: http://www.isbu-info.org/

RAM Elements will automatically find all the section properties of the sections once you program them in.  The side corrugations are pretty easy, you can use existing AISI hat sections.  The other members take a bit of work using the LEO language that comes with the program.  Also, I’ve found that it is necessary to stiffen members as you make cuts in the container.  That takes again more work with the LEO language in RAM Elements to model the sections, or conversely you could calculate your section properties by hand (not recommended, too much chance of error), or a program such as AutoCAD.

 

You are right, the ISO testing is not applicable in any way.  It assumes the containers are not cut into, and is only applicable for their use as cargo carriers.  There is no way it can be used for building, although I did see it used by an engineer in his calculations.  In case of a failure, it would make for an interesting lawsuit against the structural engineer, he would lose big time.  I hope this helps.  A copy of this e-mail is going up on my blog, with your personal information removed, since your question is very good I’d like to share it with all.

 

George

George W. Runkle III, P.E., PEng, MIEAust

Runkle Consulting, Inc.

930 New Hope Road, Suite #11-145

Lawrenceville, GA 30045

678-225-4900 (US)

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Building Your Own Computer

The computer, almost complete

Last week we realized we needed a new computer, and after a bit of debate, we ended up building our own.  The old one wasn’t able to properly handle the 3d graphics we are going to, and the processor was outdated.  We use some pretty calculation intensive software for the container design, and more and more we are designing in 3d.  Also, my son in his undergraduate curriculum is studying computer programming and game design, so the stuff he is using pushes the limits of just about everything.  The first idea was to upgrade the processor, and replace the graphics card, but when we went to the computer store (Micro Center), there was a sale on mother boards.  Then, after getting back to the office, we discovered the motherboard didn’t fit in the case of the old computer.  So, it was time for another visit to a computer store down the road to buy a brand new case.

We put everything together, and discovered Microsoft Windows didn’t want to work.  That kind of makes sense, all we had left was the hard drive.  Time for another trip to Micro Center to by Windows 7.  Then there was another discovery – the original plan was to use the hard drives that came off our old server.  They were fairly new, and large (1 Terabyte each) and we had two of them laying around.  However, they were formatted for the old server, a three disk RAID array.  The operating system would not install on them.  So, we had to install the old drive from the computer we had scrapped, install Windows on it, and then format the other two drives.

The end result was an entire weekend spent building a computer from the ground up.  How was the price?  We saved $400.00.  True, the hard drives were cannibalized from other computers, but if we bought a computer off the shelf, those drives would have sat unused.  Given my son and I are technology nerds, the weekend spent building the computer was kind of fun.  Other than the cost, if you build your own computer you can tailor it to exactly what you want and need.  So, if you feel brave, let me outline how you can do it based on my experience.

The computer, almost complete

First, unless you build computers day in and day out, it will take you much longer than you think it should.  It’s like fixing a toilet.  In my early years I worked as a plumber’s helper.  I have rebuilt I don’t know how many toilets.  However, since I don’t do that every day, I always forget something at the hardware store, and I have to make multiple trips.  One time in New Jersey the lady at the hardware store actually got mad at me because I came back twice (go figure?).  It will probably be the same for you if you build your own computer.

Also, if you don’t buy the stuff at the right place, the computer can quickly cost you much more than buying one off the shelf.  I actually was surprised this time, because previously I was able to buy computers already made that were exactly what I wanted that were cheaper.  I found in the Atlanta area that Micro Center in Duluth is very cheap for parts.  However, you may want to see what they have on sale on the floor first if saving money is your object.

Just to illustrate the price issue- we put Windows 7 Professional on the computer, and we bought the OEM version at Micro Center.  The cost?  $135.00.  Checking online, you can buy Windows 7 Professional Full Version at Office Depot for $299.99.  Understand, if you are building a new computer, you CAN’T use a Windows 7 Upgrade version.  What’s the difference between OEM version and “Full Version”?  The packaging is rather plain on the OEM version.  OEM version is to be sold to computer manufacturers.  The “Full Version” is meant to be sold to the public.  For an extra $170.00 or so you get a nice box.

Now, for the technical stuff.  Don’t expect to reuse the case your old computer came in.  Brand name computers tend to have smaller cases.  It’s probably to cut shipping costs down, and they really don’t care if they provide you with the space you might want to add stuff.  Buy a new case, and get a big one.  It will take up space, but it will be easier to work with.  You need at least 500 Watts of power for a computer with high end graphics, and a case that is well ventilated so you don’t overheat.

The next thing is the motherboard.  Don’t recycle an old one – generally motherboards are inexpensive, and the ones you buy are going to be much higher quality than the one that might come with a computer from a retail store.  Make SURE the motherboard is for the processor you are buying.  You don’t want motherboard that is for the Intel I7 processor and you are buying an AMD processor.

Obviously, you need a processor. The difference in prices for different level processors is very little until you get to the top of the line.  Then you might see as much as a thousand dollars jump in price.  It depends on what you are doing that determines the processor speed that is required.  For the most part an Intel I5 processor is good.  The higher speed processors are needed for more intense applications.  If you are using 3d software like Softplan, Revit, or other packages, get the I7.   For engineering applications, most programs will work just fine with an I5 processor, unless you are using a program that does Finite Element analysis.  Then you need an I7, because again your calculations will be intense.  There is a lot of argument about whether to use AMD or Intel.  AMD processors are much cheaper, but many people swear by Intel.  The last computer I bought has an AMD processor and I am happy with it.  My son refuses to consider anything but Intel.

Most motherboards come with graphics chips embedded in them, so you really don’t have to buy a graphics card. unless of course you are using some sort of 3d package.  CAD programs are fine with whatever comes on the motherboard, 2d graphics like you get with AutoCAD are not that intense, so this is one area you can save a lot of money.

You will need memory.  Don’t skimp here.  Even if you are just using your computer for web surfing, word processing, and bookkeeping, get a lot of memory.  Get 16 GB of memory, it will help prevent your computer from crashing if you have too many applications open, and everything will work much more smoothly.

The final thing you need is hard drives.  Generally, I don’t recommend recycling the old hard drives.  Hard drives are mechanical items, they are the one working item on your computer other than the fans that actually move.  There is a spinning platter and a moving arm that goes across the platter.  At some point in time the thing has to fail.  The longer you use the hard drive, the greater the chance it will fail.  I know I recycled older hard drives into the computer I built, but you should probably do as I say and not do as I do.  Hard drives are cheap, so risking data loss to save a few dollars is probably not worth it.  We back all our data up to an online service, so it’s a risk we are willing and able to take.

Now, as you put it all together, you need the right tools.  That means you need a good phillips head screw driver, and… well that’s about it.  You won’t get much in the way of instructions on how to put stuff together, so here are some important items:

1.  There are small brass spacers that come with your case.  They go between the motherboard and the case.  You need to use them to prevent your motherboard from shorting out on the case.

2.  Put the processor on the motherboard before you put the motherboard in the case.  There is a fan that goes on top of the processor, it has plastic connectors that go through the motherboard.  Make sure these are properly seated, otherwise the fan won’t cool the processor properly and your computer will shut itself down.

3.  Put the hard drives in the case before you install the motherboard.  That way you won’t break anything on your motherboard trying to squeeze your hard drive in.

4.  After you put in the hard drives, install your motherboard.  Remember to use the spacers.  Hold off on putting in any accessory or graphics cards, or memory.

5.  Attach the power to your hard drives and motherboard.  Attach cables from the SATA connections on your motherboard to your hard drive.

6.  Now you can put the memory, graphics card, and any expansion cards you have.  Don’t force anything, if you do you will break things and it will probably be a serious problem.  Look out for how the graphics card installs – there is a plastic locking mechanism on the motherboard that holds the card in.  I have successfully broken it on every computer I’ve worked on.  Things will still work, but the card won’t stay in well.

7.  With the computer case you should get some plastic ties.  Use these on the wires after everything is installed to keep them out of the way of fans and other items.  Pepper (my dog) got ahold of mine and I think she ate them.  Fortunately I had spares (I have a drawer of common computer stuff for emergencies).  So, it goes without saying, watch where you put stuff down and keep it away form dogs and small children.  Don’t close up the case yet.  You need to make sure everything works.

8.  When you start up the computer, it probably won’t work.  Expect this, and don’t worry (too much anyway).  You probably connected the power supply cables wrong, you’ll have to experiment on what gets connected where.  The connectors are fairly idiot proof, but there are still a number of ways you can hook power to the motherboard, and only one way will work.  There probably won’t be any documentation to tell you how to do it either.

9.  It’s fine to experiment with the cable connections.  However, disconnect the power from the computer before you change connections.  Otherwise you run the risk of frying everything.

10.  The final step – use the install software for the motherboard and peripherals to get everything working.

This whole process should take about two hours maximum, which means it will take you two days or longer.  Unless you build computers every day, that’s just the way it is.  Is it worth it?  I think it is, but the answer is dependent on how you like to spend your time.

For more information, check this series of videos on You Tube

[youtube]http://www.youtube.com/watch?v=lPIXAtNGGCw[/youtube]