6 - Plane Trusses, Frames and Machines, and Centre of Mass and Centroids Flashcards
What are the types of structures?
- Trusses
- Frames
- Machines
What is a truss?
A framework composed of members joined at their ends to form a rigid structure.
What is a plane truss?
A plane truss is a two- dimensional framework of straight prismatic members connected at their ends by frictionless hinged joints and subjected to loads and reactions that act only at the joints and lie in the plane of the structure.
What does rigid mean?
Non-collapsible
What are simple trusses?
Structures built from a basic triangle.
What is statically indeterminate?
When more members are present than are needed to prevent collapse.
What are redundant members?
Additional members or supports which are not necessary for maintaining the equilibrium configuration.
What are two-force members?
A two-force member is one in equilibrium under the action of two forces only.
What methods can be used for the force analysis of simple trusses?
- Method of Joints
2. Method of Sections
What is the method of joints?
This method for finding the forces in the members of a truss consists of satisfying the conditions of equilibrium for the forces acting on the connecting pin of each joint. The method, therefore, deals with the equilibrium of concurrent forces, and only two independent equilibrium equations are involved.
How does the method of joints work?
- Draw a free-body diagram of the whole truss. Then calculate unknown forces.
- Draw the free-body diagram of pin of chosen joint
- Solve the equilibrium equations for that joint.
- Repeat 2-3 for neighbouring joints until the answer is reached
What is external redundancy?
If a plane truss has more external supports than are necessary to ensure a stable equilibrium configuration, the truss as a whole is stationary indeterminate, and the extra supports constitute external redundancy.
What is internal redundancy?
If a truss has more internal members than are necessary to prevent collapse when the truss is removed from its supports, then the extra members constitute internal redundancy and the truss is again statically indeterminate.
