Why are trusses primarily designed using triangular shapes?

The choice emphasizing that triangles do not deform at their points captures a fundamental reason behind the popularity of triangular shapes in truss design.

When a triangle is formed, the three sides provide stability to the structure, such that if a force is applied at any point, the load is distributed evenly across all three vertices. This geometric shape maintains its form without bending or changing angles, which is crucial for structures that are expected to bear significant loads. Unlike other shapes, such as rectangles, which can distort and potentially collapse under pressure, triangles remain rigid and ensure that the structural integrity is preserved over time.

In addition to this strength and rigidity, triangles allow engineers to create efficient frameworks that can span large distances with minimal material. However, the primary reason for their use comes from the inherent mechanical properties that resist deformation under loads.