ABSTRACT
It is computationally expensive and sometimes difficult to determine the natural frequencies and mode shapes for a structure with a large number of elements using the full finite element model. For the inverse problems in structural analysis, the dynamic responses of a structure required for the system identification are usually measured, and it is difficult and impractical to obtain the responses at all the degrees-of-freedom (DOFs) of the structure. It is desirable to reduce the size of the system matrices to have a more manageable and economic solution for both the direct and inverse problems from only the responses of the measured DOFs. Such a reduction is usually referred to as the ‘model condensation method’. Another technique, called the ‘model expansion method’, to solve the problem of limited measured DOFs of a structure and the large number of DOFs of a structure is also presented in this chapter.
