Engineering Buildings Made From Shipping Containers
We began this design service back in 2007. We were approached by an individual about engineering a shipping container house in Atlanta for his personal residence. Apparently no one else wanted to touch the job. I had already worked with shipping containers in 2002/2003 in Uzbekistan when I was activated from the Air Force Reserve and was sent to Karshi-Khanabad Airbase supporting operations in Afghanistan. There wasn’t much in the way of building materials there, but it was pretty easy to have shipping container buildings provided. There were so many advantages. Much of the buildings could be fabricated off site, so you didn’t have to worry about a large workforce coming into the installation and the risk that brought on for suicide bomber. Since you can build them in units, it was easy to work out designs of what you needed, and they were durable.
Based on my experience in Uzbekistan, we didn’t see a problem with providing the structural engineering. We quit counting the number of buildings made from containers at 50.. There have been two duplexes, a single family residence, two multi family residences, an office building, military training facilities, and movable buildings for oil and mining camps in remote locations in Canada. The end users have been the Indiana Army National Guard, the Department of State, the Canadian Air Force, various mining and oil companies, and a company in Tel Aviv, Israel.
They are great for as a building material for many uses, in particular buildings that need to be wind resistant, earthquake resistant, or blast resistant. They are very useful in remote areas because they can be hauled fairly easily on a truck, and assembling on site is pretty simple.
One issue you have to consider is how specialized this work is – this type of work is not a commodity that can be designed by any architectural or engineering firm. If you look in our office, there is a whole bookshelf of references on wood frame design. We have 4 textbooks on wood design. We have the National Design Standard for Timber Construction, the Wood Frame Construction Manual, both from the American Wood Council. We have the International Residential Code, which has extensive prescriptive design information on wood. There are also about 5 different government publications we’ve obtained. It’s a pretty extensive library.
What do we have on shipping container building design? – the only book we could find, a small self-published book by Paul Sawyers. We also have the various ISO Standards about containers, which covers their dimensions, ratings, and connections. If you go through the web, there is nothing definitive on shipping containers where engineering is concerned. There are a lot of nice coffee table books with pictures, but that doesn’t help a whole lot for determining if a building can take the wind load from a Category 4 hurricane. We get calls from people all the time who point out this website or that website, but again, no website includes information on how to structurally engineer these things.
The main problem is there is no standard design for the containers. The ISO standard is a performance spec for the manufacturers. It gives loads in Kilo Newtons that the container has to carry. That works well if you are going to make a house from containers that you don’t modify. What happens when you take off the skin to open the container up? The lateral bracing disappears, as does a significant amount of it’s ability to carry a vertical load. So, if you put a bunch of the containers together, how do you know they will carry the wind load, or the live and dead loads imposed?
One way is to figure on the containers having no real strength after they are cut open, and put in a lot of steel to make up for it. That can be expensive. You can figure on the corners maintaining the strength to carry the vertical loads (probably a good assumption), and the side rails having no strength (expensive again). The way we’re trying to go about this is more definitive.
The second way, which we use, is to determine the sectional properties of the different members that make up a shipping container (Moment of Inertia, Section Modulus) and analyze the structure according to the Codes based on these sections. Because you are cutting out quite a bit of the corrugations in the steel, you lose a lot of strength, so it is necessary to go back and reinforce the various elements in most cases. However, the cost is relatively low for the additional structural work.
We found the best way to do the analysis and design is to do rough calculations by hand, and then to build a model in 3d and analyze it by computer. The work up by hand saves repeated iterations on the computer, and provides us with a check up on the results the computer provides. The repeated iterations on the computer can be time consuming, a complex building can take two hours to run all the calculations, so we try to get the number of iterations down by doing proper initial work.
To the left is how a shipping container deflects (very exaggerated) under a wind and an interior live load. This container is supported at the connection points. Look at how the roof ends up in compression, as well as the bottom and sides.
This is the code check of the model under a 40lb/sf live load in the floor, and a 90 MPH wind load. I figured that would work, the next step was to see how much wind load I could put on it before it fails. I tried 24 lbs/sf of wind load on the side, and the container is still way below the allowable stress.