Why the shape “TRIANGLE” is widely used in structural engineering?

Most of the structures that we know comprise of this particular shape “triangle” in any one of its structural systems. 

What is so important? or why “TRIANGLES”?

Just think of basic 2-dimensional geometrical shapes, what do we have? 

Squares, Rectangles, Triangles, circles, pentagon, hexagon, and the list go on.

Of these shapes, why a triangle is called the most stable shape. Let us compare these shapes and understand them.

For our example, let’s consider the square and the triangle as shown below.

Applying a force on one of the edges and studying the behavior would lead to a better understanding regarding the stability of the structure.

First, let’s try with the vertical force.

What will happen? The load applied over the square moves directly downward through the vertical member and stands still. The triangle when subjected to a vertical force through one of its edges, distributes that force evenly to either side and stands stable.

Now, let’s apply the horizontal force.

The square could not withstand this force without deformation, it tries to sway along the direction of application of the force and distort from its original shape. Whereas, applying the horizontal force tries to push one edge of the triangle.

It is not possible to move the edge without the elongation of one of its sides, this makes them stay stable for the applied force.

This simple comparison applies to all the other shapes too. Also, this can be easily verified by making a simple model with popsicles. I tried it myself, and recommend you to do so.

Let us look into a design example, where this particular behavior is utilized.

Most of us would have seen a bracing system in the steel buildings.

What is the function of bracings systems in the steel buildings?

The longitudinal forces that act on the structure are transferred to the ground with the help of bracing systems, right.

So, the longitudinal force is about to act on the edges should be transferred safely without much distortion or deflection of the system. Which is the shape that can perform this task? Obviously, the triangle.

The attached image shows several bracing arrangements that are employed in the steel structure.


This stable behavior of the triangles makes them the supreme geometry. And for this reason, they are extensively employed in the formation of trusses.

What we have discussed so far is also applied to the 3-dimensional shapes and this emphasis the use of triangle configuration in the construction of towers, electrical grids, truss bridges, and so on.

Also check out my YouTube Channel: Structures Simplified

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