When an extra support reaction is added to a truss, the redundancy is classified as:

When an extra support reaction is added to a truss, it introduces an external constraint that changes the support conditions of the structure. In structural analysis, redundancy refers to the presence of more supports or members than necessary to maintain equilibrium.

By adding an extra support reaction, you are effectively increasing the number of independent reactions available to maintain the equilibrium of the truss system, which classifies this redundancy as external. This is important in terms of analyzing and understanding the behavior of a structure under load, as it can affect how forces are distributed throughout the truss.

Internal redundancy would refer more to redundancies within the truss itself, such as having more members than necessary. Structural redundancy involves the overall framework or design that ensures a structure can still function if certain elements fail, but when an extra support is added to the truss specifically, it is considered an external redundancy.

This classification helps engineers to understand the implications of structural adjustments they may make during design or the evaluation of existing structures.