02-23-2011, 05:27 PM
The tutorials covering the anatomy of shipping containers say you can't make any modifications without weakening the container. This only makes sense. What is unclear is how much each modification would weaken the container. To play the devil's advocate the loads the container would see when functioning as a house are much less than when they are being dropped fully loaded onto a dock by a clumsy crane operator so maybe we don't need all of the original strength but the point is that now we are taking on the responsibility of figuring out how strong the container still is with the doors and windows cut in vs how strong it needs to be to function as part of the house.
If you look at most beams, trusses, and airplane wings you see certain common features. There are always solid pieces at the top and bottom. In an I-beam they are called the flanges. Second there are one or more vertical parts connecting the flanges together called the web or webs. In a house truss or in a hand made wooden airplane wing the web may consist of carefully laid out vertical and diagonal pieces that form a bunch of triangles, leaving quite a lot of open space that, in the case of a house truss, you can walk through. Some sheet metal airplane spars have simple round holes cut in the web centered along a line equidistant from the top and bottom flanges. The result is that you could take a straight edge and a magic marker and draw triangles on what is left of the web. If a hole is too large or too close to its neighbor or too close to the top or bottom, such that you can't make triangles by drawing straight lines, then it would severely weaken the ability of the web to carry shear.
Shear is the tendency of the top flange that is in compression to slide outwards relative to the bottom flange that is in tension, which wants to pull inwards. In a container supported at the ends the tension and compression in the flanges (roof and floor) would be greatest at the center while the shear would be greatest at the ends.
I haven't crunched any of the numbers myself but just going on theory of mechanics from 30 years ago, it might be OK to cut a series of small windows midway between floor and roof as long as you could still draw the required interconnecting triangles on what is left. The door, which has to go all the way to the floor and pretty near the roof, should go as close to the middle of the container as possible where the shear loads are minimal and hence the web won't be missed. What I don't know is how the corrugations affect things. Sure you can draw a straight line on the side of the container but the corrugations can stretch or compress and fail to perform the function of the solid members that would be their counterpart in a roof truss or model airplane wing.
If you look at most beams, trusses, and airplane wings you see certain common features. There are always solid pieces at the top and bottom. In an I-beam they are called the flanges. Second there are one or more vertical parts connecting the flanges together called the web or webs. In a house truss or in a hand made wooden airplane wing the web may consist of carefully laid out vertical and diagonal pieces that form a bunch of triangles, leaving quite a lot of open space that, in the case of a house truss, you can walk through. Some sheet metal airplane spars have simple round holes cut in the web centered along a line equidistant from the top and bottom flanges. The result is that you could take a straight edge and a magic marker and draw triangles on what is left of the web. If a hole is too large or too close to its neighbor or too close to the top or bottom, such that you can't make triangles by drawing straight lines, then it would severely weaken the ability of the web to carry shear.
Shear is the tendency of the top flange that is in compression to slide outwards relative to the bottom flange that is in tension, which wants to pull inwards. In a container supported at the ends the tension and compression in the flanges (roof and floor) would be greatest at the center while the shear would be greatest at the ends.
I haven't crunched any of the numbers myself but just going on theory of mechanics from 30 years ago, it might be OK to cut a series of small windows midway between floor and roof as long as you could still draw the required interconnecting triangles on what is left. The door, which has to go all the way to the floor and pretty near the roof, should go as close to the middle of the container as possible where the shear loads are minimal and hence the web won't be missed. What I don't know is how the corrugations affect things. Sure you can draw a straight line on the side of the container but the corrugations can stretch or compress and fail to perform the function of the solid members that would be their counterpart in a roof truss or model airplane wing.