Truss is an assembly of bars joined at the ends in such a way as to create a two- or a three-dimensional structure. For stability consideration, a truss generally consists of one or more triangular cells as building blocks.
Each truss memberis a straight and uniform axial bar made of a homogeneous material. The points where members are joined together are called joints. These joints are treated as hinged points incapable of supporting any moment.
The external forces are applied only at the joints. These forces are often parallel, but generally non-concurrent. A two-dimensional truss with all members and forces in the same plane is also known as a planartruss. A three-dimensional truss is also known as a spacetruss.
Looking at the 2-D truss shown below, we see that it consists of 13 members and 8 joints. A truss member can only support a force along its axis, which would either pull or push on it. If the member is being pulled, it is said to be in tension, and if it is being pushed, it is said to be in compression. The free body diagram of member 5 shows the direction of the axial force if the member is in compression.
Important Facts about Trusses
1. Joints are treated as smooth pin connections.
2. Members are connected together only at the joints.
3. External forces are applied only at the joints.
4. Because a truss joint is modeled as a hinge, no moment can be applied at a joint.
5. All truss members are two-force members that are either in tension or compression.
6. In a two-dimensional truss, all forces must be in the plane of the truss.
7. The weight of each truss member, if considered, has to be divided in half and applied at the end joints.