Page 45 - 4749

Note that the potential energy is always positive, and in its
calculation we cannot use the principle of independence of the
forces between U and P since there is no linear relationship.

2.10 Statically indeterminate system

Systems for which it is impossible to determine the reaction in
the necks or internal force factors, using only the equations of
equilibrium, are called statically undetectable.
The difference between the number of unknown forces and the
number of independent equilibrium equations that can be passed to
the system, is called static degree of uncertainty. Recall that the
equilibrium conditions of arbitrary planar system are reduced to
writing three equations of statics

Figure 2.13

X  0 ; Y  0 ; M  0 . (2.37)
i
For solving the static uncertainty, that is to find the unknown
forces in statically undetectable system it is necessary to add to the
equilibrium equation (2.37) equations describing the deformation

45