Abstract
The concepts of the degrees of indeterminacy and instability, which are the important mechanical properties of frame structure, are described from the general point of view. Each member is assumed to be totally rigid but has the deformable ends to calculate compression, shear and bending algebraically and hence the symmetrical relationship between the equations of equilibrium and compatibility appears without using the differentials of deformation. It is interesting to find that the unique equation is derived among the numbers of member force, the degree of freedom, the degree of indeterminacy and the degree of instability. Particularly it is remarked that the geometrical configuration of frame should be considered to count the the degrees of indeterminacy and instability as well.
