F₁ = 200kN

Equating (A) thus gives

200+ 100 + F₃ =0

F₃ = -300kN

-ve sign shows that assumed direction was opposite to actual direction.

Observe that this problem is otherwise a statically indeterminate problem. However we have been able to find out forces in three required members.

SPACE TRUSSES

A space truss is the three-dimensional counterpart of the plane truss. The idealized space truss consists of rigid links connected at their ends by ball-and-socket joints. A space truss requires six bars joined at their ends to form the edges of a tetrahedron as the basic non-collapsible unit.

We may form a new rigid unit to extend the structure with three fixed joints on the existing structure.