1. How Much Weight Could the Same Spaghetti Hold in the Bridge Experiment?
This experiment was published in the 2008 issue of *Rika News* (Shonen Shashin Shinbunsha) and was supervised by Satoshi Izumi from the University of Tokyo. [5] They connected 40 thin spaghetti sticks with hot glue to form a bridge shape and applied a load. The bridge that was simply bundled together could not withstand a load of 2 kg. However, the bridge that was built by combining triangles, referencing a truss bridge, did not break even when 4 kg was hung from it. [5]
However, this is just one example of an experiment done under specific conditions. It is not a law that "if you make triangles, it will always withstand more than twice the weight." Still, the fact that a difference appeared by changing only the arrangement without adding more material is the starting point for the following sections. [5]
2. Why Triangles Keep Their Shape Better Than Squares
If you connect 4 thin sticks to make a square, it tilts into a parallelogram just by pushing the joints with your fingers. This is because even if the lengths of the four sides are fixed, there are infinite possible shapes for a quadrilateral. [1]
Triangles are different. When the lengths of the three sides are fixed, the angles are also fixed, and the shape becomes unique. Therefore, even with pin joints where the connections can rotate freely, a triangle can maintain its shape. [1] The English Wikipedia also explains that the triangle is the simplest figure whose shape does not change when the side lengths are fixed. [3]
The deformation where a rectangle collapses into a parallelogram is called "shear deformation." In this process, one diagonal stretches while the other shrinks. If you add one diagonal member (a diagonal brace) to a square, this deformation can be prevented. [1] For example, adding a diagonal piece of wood to a door frame makes it less likely to warp, which is a similar image. However, in the case of a truss, the point is slightly different: triangles help the truss keep its shape, assuming the joints can rotate. [1]
3. Why the Middle of a Bending Bridge Is "Not Working"
When a car passes over a bridge, the bridge bends. At this time, the top side compresses (shortens), and the bottom side stretches (lengthens). The area near the middle between the top and bottom (near the neutral axis) hardly stretches or compresses at all. [1]
Since the middle part has little work to do, could it be removed? The idea is to "hollow out" the middle and connect the remaining top and bottom with diagonal members. This creates the shape of a truss. [1] Note that "hollowing out" is a metaphor for explanation. This is a way of thinking to explain mechanics, not a statement that trusses were historically invented in this order.
Unlike concrete bridges or bridges built with brick, truss bridges are said to be able to be made light and strong because they support the beam with a framework. [8] By arranging members with small cross-sections into triangles, it is possible to span long distances. [1]
4. Why Pushed Sticks Are Made Thicker Than Pulled Sticks
If you push a thin stick from both sides, it bends suddenly in the middle. This is called buckling. Therefore, members that are pushed (compression members) are often made thicker. Members that are pulled (tension members) are less likely to buckle, so they can have a relatively thin cross-sectional area. [1]
In the bridge introduced in the materials (the Ichinoto Bridge), there is a section near the center where diagonal members cross in an X shape. Depending on the position of the car, the force acting on the same diagonal member can change between tension and compression. It is explained that using two thin members for tension is more material-efficient than using one thick compression member. [1]
In an ideally considered truss, only tension or compression forces act on each member, and bending and shear are said to be nearly zero. [3] However, since actual joints are not perfect pins, this is a matter of calculation.
5. How Triangles Support Roofs in Japanese and Western Roof Frames
The framework that supports a house's roof is called a roof frame. Traditional Japanese *koya* (Japanese-style roof framing) supports the weight of the roof with vertical posts called *koyazuka*. In contrast, *yo-goya* (Western-style roof framing) is a type of roof frame that incorporates diagonal members and is said to be used in wooden houses built with the two-by-four method. A terminology collection also explains that it is strong against horizontal forces. [4]
According to materials from the Hokkaido Prefectural Forest Products Research Institute, in *koya*, bending forces act on the tie beam due to the roof's weight, requiring a large cross-section for the tie beam. In *yo-goya* made into a truss, bending forces do not act on the members, so the bottom chord (the lower horizontal member) can have a smaller cross-sectional area. [2]
The same materials state that as of 1984, lightweight wooden trusses are the mainstream for residential roof frames in countries like the United States, but in Japan, they have hardly spread because traditional method roof frames have been rationalized. [2] The current situation is not clear from this 1984 source.
6. How Triangle Frameworks Were Used in the Old Ibi River Railway Bridge
The former Ibi River Bridge was a railway bridge that spanned the Ibi River in Gifu Prefecture. The bridge was 325.1 meters long and began being used on the Tokaido Line between Gifu and Ogaki in 1887 (Meiji 20). Five wrought-iron trusses, each 200 feet (about 61 meters) long with pin-connected joints, were lined up. The design was by British engineer C. Pownall, and the members were made in Britain. [6] It was designated as an Important Cultural Property in 2008. [6]
Another example is the Katsura River Bridge on the Tokaido Main Line, built in 1911 (Meiji 44). It is said to be one of the first truss bridges made in Japan. It is a pony Warren truss, and according to the article, it is still used on the down line as of April 2026. [7] Since the text uses phrases like "one of" and "said to be," it is better not to definitively say it was the first in Japan.
7. Where to Find Triangle Frameworks in Everyday Places
Let's look for trusses in familiar places. It is said they are used in civil engineering for iron towers and bridges, in architecture for roof frames and domes, and in machinery for crane arms and bicycle frames. [3]
If you find one, compare how many triangles are connected, whether the diagonal bars are thick or thin, and if there are places where they cross in an X shape. Thick bars might be compression members, and thin bars might be tension members (see section 4). Enjoy this as a prediction. [3]
Near roads or railway tracks, do not stop; observe from a safe place, preferably with your family.