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続 3Dプリンターの家 住宅ローンから世界は脱却できるか?

Continued 3D Printed Houses Can the world break away from mortgages?

Photo from Obayashi press release https://www.obayashi.co.jp/news/detail/news20220610_1.html

The other day, I wrote about 3D printed houses on my blog, and I discovered that we are very close to commercialization (can you even call it close?).

Started construction of a building using a 3D printer using a structural format certified by the Minister of Land, Infrastructure, Transport and Tourism for the first time in Japan https://www.obayashi.co.jp/news/detail/news20220610_1.html

The other day, I wrote about 3D printed houses by a company called Serendix, and it seems that there are many companies in Japan that are researching and developing 3D printed houses, but Obayashi seems to be one step ahead of them.

Basically, there are three types of routes for structural design based on the premise of applying for a building permit (this has been going on for a long time, so I apologize if I'm wrong, but it's roughly like this)

Route 1 Small building No structural calculation required

Route 2 Medium-sized buildings Allowable stress calculation (also known as temporary design) Calculate and design components so that they will not be damaged by small earthquakes (below the allowable stress)

Route 3 Medium /Large-sized Buildings Perform allowable stress calculation (temporary design) + horizontal strength calculation/limit strength calculation (also known as secondary design) to avoid collapse while allowing damage in the event of a major earthquake. (Nonlinear portion exceeding allowable stress and below breaking strength) should be calculated and designed to avoid such damage.

The majority of buildings in the world pass the certification application by roughly following three routes.

As mentioned in the previous article, ``3D Printed Houses: Can the World Get Away from Mortgage Loans?'', there is no structural calculation method for unreinforced concrete structures.

Roughly speaking, concrete can withstand 21N per square millimeter in compression (roughly 2.1 kg, 210 kg per square centimeter, Fc21), but it is so weak that it can be ignored in tension. In other words, there is no calculation method under the current Building Standards Act for the tensile strength of concrete. I can't calculate it. Therefore, concrete structures do not exist as concrete alone, but can only exist as reinforced concrete structures (RC) with reinforcing bars or steel reinforced concrete structures (SRC).

This is because steel has the opposite properties to concrete, being weak in compression but strong in tension.

(Actually, it is not weak; it is usually used in the form of steel frames or reinforcing bars, so there is a buckling phenomenon in which it snaps when compressed.It is not that it is weak against compression, but it is resistant to tension. It exhibits very good performance - a normal construction steel frame can withstand a tensile force of 400N per square millimeter.

Therefore, when constructing a structure using concrete (except for the foundation part), concrete that is strong in compression (and can be calculated for compression) and reinforcing bars or steel frames that are strong in tension (can be calculated for tension, etc.) For medium-to-high-rise buildings, only steel-framed reinforced concrete (or steel-framed reinforced concrete) can be used in combination with steel-framed reinforced concrete. This is a bottleneck that is preventing the spread of 3D printers from progressing.

In other words, since structural calculations cannot be performed and there are no provisions in the Building Standards Act, an application for confirmation cannot be granted.

This is the reason.

However, in reality, in addition to the three structural design routes mentioned above, there is a fourth route.

that is,

Route 4 Route certified by the Minister of Land, Infrastructure, Transport and Tourism

  • A skyscraper (I think the definition of a skyscraper is 33 meters in height...)
  • Items not specified in the Building Standards Act
  • Other advanced structural calculations that cannot be handled by local building officials.

The method involves conducting full-scale vibration experiments, full-scale wind tunnel experiments, time-chronology response analysis (computer simulation using actual seismic waves), etc., and is certified by the Minister of Land, Infrastructure, Transport and Tourism as a method that can confirm a high degree of safety. There is.

Using this method, it is possible to pass a building permit application even with an unreinforced concrete structure.

It appears that the 3D printed building that cleared the certification application using this ministerial certification route was developed by Obayashi Corporation.

As expected from a major general contractor, the research department must be huge, and I'm sure there are a lot of researchers with Ph.D.'s.

Apparently they have even developed concrete that is perfect for 3D printing. (Special mortar for 3D printers, ultra-high strength fiber reinforced concrete)

I see. Apparently, by mixing ultra-high-strength fibers (it's not mentioned what they are) into the concrete, tensile strength is achieved in place of reinforcing steel. Compressive strength 180N/mm², tensile strength 8.8N/mm², bending strength 32.6N/mm².

This gives the sense that Obayashi is clearly leading the way in domestic 3D printed housing development.

However, I feel that 3D printed houses built by major general contractors are not cheap.

Personally, I have high hopes for Serendix's philosophy.

I will repeat this over and over again, but the reason why 3D houses have not become so popular in Japan is that structural calculations for unreinforced concrete are impossible under the Building Standards Act, and to overcome this, it is extremely difficult (almost all major general contractors are required to do so). This is because there is a feeling that the game has no choice but to go through the ministerial certification route (which can only be done by other players) (a game as impossible as Makai Village, which used to be on the Famicom).

In America and the Netherlands, there are no earthquakes or typhoons, and building laws are probably more lenient. Well, in Europe there are almost unreinforced concrete block, masonry, and brick structures, so there are probably no legal problems with houses printed with 3D printers.

Can the world break away from mortgages? The world can. Japan is? what about?

Should we just wait for the law to be amended?

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