Eigenvalue analysis

The efficient Lanczos algorithm [Hughes, 1987] is used by default for the evaluation of the structural natural frequencies and mode shapes. However, the Jacobi algorithm with Ritz transformation may also be chosen by the user in the Advanced Settings module.

Eigenvalue analysis is a purely elastic type of structural analysis, since material properties are taken as constant throughout the entire computation procedure. However, in SeismoBuild inelastic frame elements are used, that will be employed in all the analyses, including the eigenvalue one. Hence, different material and section types are employed in the characterisation of the elements' sectional mechanical properties, which are internally determined by the program, using classic formulae that can be found on any book or publication on basics of structural mechanics [e.g. Gere and Timoshenko, 1997; Pilkey, 1994].

Note: Concrete confinement will increase the compressive strength of the material, and hence the stiffness of the member, leading thus to shorter periods of vibration.