Details

As shown in the FBD, the forces holding the plate in equilibrium are described by a system of three independent equilibrium equations ( and ). Because there are also three unknowns for the supporting force, the problem can be solved.

Snapshot 1: the load force is inside the triangle; the three columns are load-bearing with compression

Snapshot 2: the load force is outside the triangle; two columns are load-bearing with compression, one column holds the plate by downward tension

Snapshot 3: the load force is on the equivalent center; the three columns are load-bearing with equivalent compressions

Engineers can select the position of the load force to determine the forces exerted by the three columns.

Reference:

A. Pytel and J. Kiusalaas, Engineering Mechanics: Statics, 2nd ed., Beijing: Tsinghua & Thomson, 2001, pp. 209, 227–228.