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This is a truss. The DOSI is:
Reactions (r = 4)
There are two pinned supports. A pinned support has two reactions (lateral, vertical).
Joints (j = 6)
There is a joint at every reaction, free end, and intersection of elements.
Truss Members (ntruss = 9)
There are nine segments.
Degree of Static Indeterminacy (DOSI = 1)
r + ntruss – 2j = 4 + 9 – 2(6) = 1
StructNotes 