The truss

This is one of the most famous architectural structures in the world — the Eiffel Tower. It was built at the end of the 1880s. At 300 metres, it was the tallest structure on Earth for 40 years after its completion. Many people consider the Eiffel Tower a symbol of France, and an architectural wonder. And it is indeed a unique structure.

The Eiffel Tower isn't solid all the way through, but it is still really strong and sturdy. If you look closely, you’ll notice that it’s mostly made up of triangles. It's these triangles that make the structure so strong and allow it to be so tall. How come? Let’s demonstrate it with a little experiment.

You’ll need some popsicle or craft sticks, a few drawing pins, and a few pieces of cork or rubber eraser. First, take four sticks and use them to form a square. At each corner, drive a drawing pin through both sticks to connect them. Secure the sharp pin ends on the back with the cork or eraser. Now, holding the bottom stick, push on one of the corners at the top.

The square deforms and turns into a rhombus! Next, take another stick and join it with the other four, so it forms a diagonal. Try to push on one corner again. It’s so sturdy it won’t budge! The diagonal “brace” splits the quadrangle into two triangles.

The triangle is a unique geometric shape, in which the angles inside are defined by the length of the sides. So it is impossible to deform a triangle by changing its inner angles, without changing the length of its sides. You can try to add a few more sticks to your structure, forming more triangles. You’ll see that the structure remains stable and rigid. And by adding more triangles like that you create a type of structure known as a truss.

A truss, made up of many triangles joined together on one plane, takes advantage of the geometric stability of triangles. Triangles in truss structures are made of rigid bars — often wooden or metal. These bars can transfer squeezing and pulling forces – compressions and tensions. Within the truss, tensions and compressions balance each other out. When a force is applied to the truss, each bar carries the compression or tension along its axis to the neighbouring joint.

The force is carried along the bars like that to other supporting elements, such as beams and columns, until it is finally transferred to the ground. The structure remains stable, while the weight and other forces are evenly distributed. When many trusses are connected together, even a very large weight can be efficiently transferred in multiple dimensions. All trusses are made up of adjoining triangles, but besides that they might have very different designs. The design depends on the forces it's supposed to carry, or the purpose for which the truss is used.

Trusses are especially useful in situations where weight needs to be carried across a wide span. So, they are commonly used when building bridges, or to support roofs of large buildings, such as hangars, airports, or large stadiums. You can also often find trusses in tall vertical structures, such as construction cranes, or transmission towers that support power lines. And, as the example of the Eiffel Tower proves, trusses can be used for more than structural support! Trusses can be a design element, beautifying the architectural landscape and attracting tourists!