Builders guide to Shipping Containers
Sunday, February 14th, 2010The ISO Shipping Container is a terrific pice of hardware. Cheap (500-3000 €), sturdy (structure can carry 200-350 tonnes), corrosion resistant (usually made of CORTEN) and good looking.
They are terrific for building things and while it is an urban legend that “it’s cheaper to scrap them then to send them back to Asia” (hint: the ships have to drive back to Asia anyway) new containers are produced in China or Korea and used containers are cheap and easy to get in Europe and the US.
Things you can’t do with shipping Containers
All these great features come with a bunch of restrictions. Containers come with 8 Corner Casings which are the only points where a Shipping Container is meant to be anchored. This makes a container can only rest on it’s 4 bottom Corners and can only support loads from above on it’s 4 top corners.
Everything else on a container is not meant to carry any significant load.
This meant you can only stack containers in configurations where all for bottom corner casings of the upper container are supported by four top corner casings of lower containers.
This results in many desirable stacking configurations being impossible from a stability standpoint. See for examples on the right.
Nearly all configurations where the upper container is rotated by 90 degrees are impossible. Putting 20″ on 40″ containers is in most cases impossible.
Putting a 40″ on a single 20″ container is impossible. Most overhang configurations are impossible.
Now you know the reason why there is so little creativity in professional Container Stacking.
What works is putting a 40″ Container on two 20″ containers, but there is little reason to do that.
The Roof Problem
While the floors of a Container are meant to carry loads from more than a ton per square meter the roofs are little more than weather protection than a few dozen kg per square meter. See this video of me seesawing my toes and the effect on the roof.
Walking on the Roof for a single person is slightly uncomfortable and for a group it is something in-between scary and dangerous. The high quality steel sheeting of the roof will not break but the whole thing is very shaky.
Also the roofs of pre-owned containers are usually not flat anymore. Being the most fragile part of the structure they have a tendency to bent and get into a wobbly state.
So if you plan to walk regularly on them you need to put additional flooring on top of the containers to distribute the load and stiffen the floor. We used two layers of 1 cm plywood which is fine, but still the walking experience is not totally solid.
If you plan to put heavier loads on the roofs you probably need to discuss this with a structural engineer. An approach we where contemplating was to add an additional layer of containers on top and remove roof and walls from them to keep only the ultra rigid container floor. Puma City this this for their balcony
Steel on Steel
You might or might not be aware, that steel on steel usually results in an excellent plate bearing. Meaning that Corner Casings on top of each other result in astonishing easy movability of the upper container. As in “Slam the door and it falls nearly down”. Even a pice of carton between the corner casings helps somewhat. But on the long run you need to fix your containers onto each other.
So it’t imperative that you fix the upper container to the lower containers. The best way is to use Twistlocks as the Pros do. Marine grade Twistlocks can secure a stack of 4 fully loaded containers on a rolling ship without additional help. (Usually contianers are stacked 6-8 levels high, which results in the need for additional securing. We bought our Twistlocks at Willi Wader Group.
You might be tempted to save the expense of twistlocks (15-30 € per lock) and instead screw or weld the containers together. But keep in might that the twistlocks are mass produced to rigid quality standards – while it is hard to assess the integrity of your home grown connection approach.
Doors
Doors of shipping containers are hard to open by design. Even on a brand new container you have to operate two handles with considerable strength at once and at different speeds to open and close a container. And you can not open the left dor unless the right door is already open (although you might bee able to change that with a welding touch, a knife and in 20 minutes).
On a pre-owned container being 10 years or so old it is usually much harder to operate the doors because the frame of the door and the container itself is always bent to a certain degree. These doors can not replace a normal door if you are planning to pass it several times a day.
If you receive more than one container sort them by door quality. If you are able to choose the containers before purchase, always check the doors.
Structural integrity
Shipping Containers are unibody constructions. This means the whole hull is used to contribute to load distribution.
In case you didn’t suspect: this means bad things™ happen, if you cut substantial holes in the hull.
If you spot something with big openings it is no shipping container. Or it is a shipping container which has extensively upgraded structural components – which is possible but defeats the purpose of “standardized, cheap, reusable”.
Even if you leave the door open the container is less sturdy than one wit a closed door. Most containers seem to be able to withstand removing the back wall opposite to the door I wouldn’t like to have any load on such a container.
We opted for leaving about 30 cm on the top and about 15 cm at the sides to keep some reinforcement. But in our application we are quite sure that there are only minimal shear forces. I would not feel comfortable in removing the back walls in any container which would have to carry substantial load.
If you remove one of the longer walls your container is toast. Or at least it has as much integrity as toast. We removed a complete wall of a container and found out that the container lost all stability.
While all containers conform to rigid standards (ocean carriers hate delays due to broken containers) not all containers are created equal. Some are a little less unibody by having additional reinforcement along the top. Use this type for cutting holes in the sides – they even can keep a somewhat stable roof when a whole wall is removed.
What feels like a relative comfortable solution is removing about 20% of the side wall at the right and at the left end while leaving the upper 30 cm of the wall intact. The result is a still very stable container.
Where to get containers and what to get
You can get containers at shipping companies and ad specialized container providers. The only ISO containers we where able to get at decent prices where 20″ 40″ and 40″ “high cube” containers. Keep in mind that the “modular space” container type is very different from shipping containers and usualy much less sturdy.
We bought containers still sea-worthy and with next CSC inspection scheduled for 2011 or 2012. The Containers where commissioned 1994-1997 and considered “C” quality (on a ABC scale) by the shipping company. Because of the doors and possible holes (in C quality containers or in containers not sea worthy) you should inspect the containers before buying if possible.
The floors differ much between containers and usually are contaminated by pesticides, plan to remove them if humans will spend serious time inside. Some of our containers where freshly painted on the inside and it took several weeks of venting to get the smell to a bearable level.
How to move the containers
Usually the party selling you the containers has the equipment for hauling them to your side. The first issue is getting them of the tuck and the second issue is getting them where you want them.
We rented a 8 ton fork lift for all the handling which was adequate but not over powered for the task. 
When carrying two containers at once (nominal weight 5 tons) the machine had considerable effort. While considering my self an seasoned fork lift driver (30 years of experience) I had to learn that a huge forklift with a huge container is something very different than the kind of forklift you drive in warehouses. A Container has lot’s of momentum and you see absolutely nothing in the direction you are driving at. For a 20″ container assume every corner with less than 8 m space requires artistic driving capabilities. We had to get around a 6.5 m corner and through a 4 m door. We handled that by carrying the containers between the big 8 t forklift and one of our own 1.5 t warehouse-forklifts.
When renting a forklift be sure to get one which can spread it’s forks wide enough to fit into the carrying lashes at the belly of a container. They are 2.5 m or so apart.
Big forklifts can only operate on relatively even ground. Alternatively you can use a crane. The main problem with a crane and especially 40″ containers is that you can not introduce big horizontal forces by the attachment cables running from all for corners to the hook. Since you probably don’t have a spreader available to distribute the load you either need a very tall crane or two cranes. Your crane operator probably can tell you more.
Placement
Containers are build to stand on their four lower corner casings. If you don’t have a flat sturdy surface to put them on you should build a foundation at the four corners. Directly insert twistlocks into the foundation during pouring for perfect stability.
Containers are not insulated against heat, cold, noise and vibrations. If you insulate them on the outside you loose the feature of the weatherproof shell and if you insulate them on the inside your rooms get very small. It’s also hard to make the connection between two containers waterproof. Therefore it seems very popular to put the containers into another building to provide heating and shelter.
Further Reading
More information on the real world issues of container construction can be found at 10 Things to Consider in Using Shipping Containers for Your Next Project. Preston Koerner has good points although we where able to get the containers much cheaper than his estimate of 2000-4000 U$. We payed less than 1000 € per 20″ (including delivery).
