Why is the triangle shape so important in truss design?

Answer 1

It is the only truly stable shape. Any shape with more than three sides is highly susceptible to horizontal and vertical movement. Any shape with less than 3 sides is well... not a shape.

Answer 2

There are three main reasons why:
Rigidity
A triangle has three sides and three angles, and each angle is held solidly in place by the side opposite it. This means that a triangle s angles are fixed, and that if pressure is placed anywhere on a triangle, its angles, unlike those of other shapes, will not change.

Forces
When a force is applied to a triangle, the resulting pressure is directed sideways rather than down. This means that sides of the triangle are in either compression or tension, and that there is thus no bending movement.

Openness
Since the center of a triangle does not contribute to its geometric rigidity or structural integrity, the center of a triangle can remain open. As one of the goals in erecting a truss is minimizing its weight, triangles are an appropriate shape to use.

Answer 3

Triangular Truss Design

Answer 4

Because the forces in each of its two main girders are essentially planar, a truss is usually modelled as a two-dimensional plane frame. If there are significant out-of-plane forces, the structure must be modelled as a three-dimensional space frame.

The analysis of trusses often assumes that loads are applied to joints only and not at intermediate points along the members. The weight of the members is often insignificant compared to the applied loads and so is often omitted. If required, half of the weight of each member may be applied to the adjacent joints. Provided the members are long and slender, the moments transmitted through the joints are negligible and they can be treated as "hinges" or 'pin-joints'. Every member of the truss is then in pure compression or pure tension -- shear, bending moment, and other more complex stresses are all practically zero. This makes trusses easier to analyze. This also makes trusses physically stronger than other ways of arranging material -- because nearly every material can hold a much larger load in tension and compression than in shear, bending, torsion, or other kinds of force.

Structural analysis of trusses of any type can readily be carried out using a matrix method such as the matrix stiffness method, the flexibility method or the finite element method.


[edit] Forces in members

Answer 5

Its too hard to make trusses in circles.

Answer 6

Simply put:
Because it's the only shape whose rigidity
is maintained if the joints can pivot.
(A lot proceeds from that.)