All structures, regardless of how simple the construction, possess more the one degree of freedom, However many structures can be adequately represented as a series of SDOF systems for analysis purposes. The accuracy obtainable from a SDOF approximation depends on how well the deformed shape of the structure and its resistance can be represented with respect to time. Sufficiently accurate results can obtained for primary load carrying components of structures such as beams, girders, columns, wall panels, diaphragm slabs and shear walls.