# Making shipping containers with wood instead of steel, is my calculation sound and valid?

For making shipping containers easily reusable as structural components for modular buildings, and reducing their carbon footprint, we want to made their structure out of wood instead of steel.

Imagine mass producing wood shipping containers with building features (insulation, windows, plumbing and wires) in a manufacturing cluster city, all kinds of finished goods are packed inside these containers and shipped to a consumer market where the containers are stacked up to become permanent buildings.

According to wikipedia, Shipping containers should have a stacking strength to withstand a superimposed weight of 216,000 kg, allowing stacking a total of 7 layers, 36,000 kg maximum for each layer.

Pine is the most abundant and affordable wood in the US. According to matweb, pine has a compressive strength of 33 MPa along the grain.

If we use pine for the 4 corner posts in the 4 corners of a shipping container, the minimum cross section of all 4 corner posts combined is 216000*9.8/33e6 = 0.064m2.

• Ideal load distribution: each corner post only need 0.016m2 (about the size of a common 6inx6in lumber).

• worst case load distribution: all stress is concentrated on one corner. We need 4 lumbers sized 6inx6in for each corner.

• What bugs can be transported with the wood? Commented Jun 25, 2023 at 9:17
• As @SolarMike is implying, some countries ban the importation of wood to prevent the unwanted importation of pests, including wood borers & potentially spiders that would find wood preferable to metal for building webs (homes). The ban on wood imports also applies to tourist items such a carved bowls or wooden figurines. The other thing to consider is how to attach the horizontal beams to the posts so the cross sectional area of the posts is not reduced & to secure a strong connection between post & beam.
– Fred
Commented Jun 26, 2023 at 4:32
• @Fred Chemically treated lumber (e.g.ACQ as pictured) is inhospitable for pest and fungus. Containers use corner blocks that connect with 3 structural members. Finger joint is a common carpentry solution joining wood with adhesive. Commented Jun 26, 2023 at 23:25
• Threated lumber is even worse. My dad nearly died from resawing some crates sent from Brazil. The crates were Purple Heart and Brazilian Rosewood. But they were treated for import into the US. Bizarrely, the chemicals which were approved for treating imported timber were themselves banned for sale or use in the US. It took me almost a month to figure out what happened and trace the chemicals back to Dupont and get the information to my dad's doctors at the hospital. My dad suffered from neuropathy for the rest of his life, But his woodshop looked really nice paneled in rosewood, Commented Jul 27, 2023 at 0:15
• @PhilSweet yeah, the old woodworkers i know all have really nasty stories with exotic wood. Threated and untreated... Commented Jul 27, 2023 at 10:30

Thing is shipping containers are, generally cheap due to multiple reuse. Used ones are frequently sold at prices that don't even cover the material cost if I were to build my own.

Metal is easy to repair as long as its not rusted too much. I can cut it, I can weld it, I can polish it. So it retains some value, in worst case scenario i can sell it for scrap.

Now as for the lumber one? Well, for one in my location its hard to get rid of chemically treated wood. Your not allowed to burn it and you have to pay for disposal. Then the rules for the allowed chemicals and processes vary from place to place. Finally its not as reusable, the damage to it is not as easily fixed as a metal container.

So it does not actually sound like a super good deal to me for a global transport solution. But locally, why not.

My main criticism is why you are using a shipping container footprint for something you are building yourself. The advantage of shipping containers is they are everywhere already. Pre-fab wooden structures are already a thing.

Beyond that, a 6x6 wood frame structure doesn't meet the sniff test for being anything near as robust as a steel shipping container. No one would expect such a structure to be rated to support hundreds of thousands of pounds.

The last would be getting this design past zoning and code enforcement organizations.

• my answer: save shipping cost by piggyback to the consumer goods shipping routes, e.g. Walmart. Prefab wooden structures are huge and hollow they cost a lot to ship across distance, thus market coverage and thus factory scale is limited. Prefab container building elements are huge and hollow too, but they can be filled and shipped together with consumer goods. !drawing Commented Jun 26, 2023 at 23:34
• Can you please point out my mistake in calculation? Why is a 12x12 (consider 4 6x6s bundled together) column unable of bearing 216000 kg of pressing force along grain? Commented Jun 26, 2023 at 23:40