A truss structure is made of either metal, wood or concrete elements (rod, beams or even cables if the element is in traction).
The elements are connected together using revolute joints, that allow free rotation, hence they do not transmit any torque.
This constructions guarantees that the elements are either purely in tractions or purely in compression, with no flexion whatsoever.
This is a very useful mechanical property since few materials can offer strong flexion resistance.
Examples : cranes, wide span roofs, bridges, electric pylons, Alex Moulton bicycle.
The problem:
Given the geometry of a structure : vertices (joints) and edges (mechanical elements), beams or cables, joining those vertices,
given how the structure is anchored to the ground (resulting in forces for which we know the direction but not the intensity),
given anumber of known load forces (direction and intensity) applied to the structure,
calculate the force in each element of the structure (traction or compression) and the force in the anchors linking the structure to the ground.
Assumptions:
Weight of the structured is considered negligible compared to the external loads applied to it.
It results in simple equations : forces at each joint must sum to zero