Eigenvalue programs for building structures

This paper presents two eigenvalue routines for calculating the mode shapes and frequencies of engineering structures, in particular, building structures. Both routines are developed on the assumption that the mass matrix is diagonal, with all diagonal terms non-zero, and that the stiffness matrix is symmetric. The inverse power method with shifts is used in each case; the only important differences between the two routines is in the allocation of stroage and in the procedure used for inverting the matrices. Illustrative examples are presented to demonstrate the computational efficiency that can be achieved by the use of the inverse power method with shifts, provided the shift points are located judiciously and an appropriate convergence criterion is employed.