Is a truss considered statically determinate?

A truss can be classified as either statically determinate or statically indeterminate, and the correct classification depends on certain conditions related to its design and support. A statically determinate truss is one where the external forces and reactions can be determined solely through equilibrium equations without needing to consider material properties or deformation.

For a truss to be statically determinate, it must have a specific ratio of members to joints. A basic condition is that the number of members must equal two times the number of joints minus three (2J - 3), and all supports must provide sufficient constraints to maintain equilibrium without redundancy in the force resolution. If the truss meets this criterion and does not have extra members or supports, it is considered statically determinate.

In contrast, if the design of the truss has additional members or constraints that do not allow the identification of internal forces solely through equilibrium equations (for example, having more members than necessary), it is considered statically indeterminate. This situation requires more advanced methods, such as the use of compatibility equations or material properties, to solve for the internal forces, leading to greater complexity in analysis.

Therefore, the assertion that a truss is not considered statically determinate under all circumstances is