This book provides the relationship between the static stiffness and modal stiffness of structures. The applications of the use of these relationships will be also presented as reveled in physical structures. In the understanding of a structure, the stiffness of the structure is one measure of the ability of this structure, so that an understanding of the stiffness is very important. Stiffness is the ability of a structure to receive the loads are compared with the deformation that occurs in these structures. The higher the value the greater rigidity of the structure the ability to receive...