3D Frequency and Spectral Analysis

 

R/C BUILDING software can be used to evaluate the Natural Periods of a building’s structural system and to perform a Spectral Analysis. Frequency analysis evaluates mode shapes and associated natural periods (T, seconds) or frequencies (f, Hz) of the structure based on its stiffness and mass properties. Spectral analysis evaluates the maximum values of the displacement and the internal forces generated by an external dynamic (time dependant) load.

R/C BUILDING software offers 2D and 3D frequency analysis methods to evaluate the mode shapes and natural periods, and to perform Spectral Analysis:

2D Simple
The dominant mode shapes in X-X and Y-Y are evaluated reliably. An initial set of lateral forces are required in order to evaluate the mode shapes (Higher mode shapes are estimated, and the rotational mode shapes are neglected). This method may be used for regular structures, or only when the dominant mode shapes in X-X and Y-Y are of interest. This method can also be used to confirm and check the dominant periods obtained by the more advanced methods.

2D Advanced
The first several mode shapes in X-X and Y-Y are evaluated reliably. An initial set of lateral forces are required in order to evaluate the mode shapes. This approach is reliable for relatively regular structures. The rotational mode shapes are neglected. In both 2D approaches defined above, the structure can rotate about the vertical axes but the rotational modes shapes are not evaluated. The translation of the each level is represented as an average of the four floor corners. If the floor rotation is significant then the translational mode shapes are not very reliably presented.

3D Complete
All mode shapes, translation in X-X and Y-Y, and rotation about the vertical axes are evaluated reliably. If sufficient number of mode shapes are evaluated the Mass Participation Factor in each orthogonal direction will be greater than 90%. This is the most reliable method for dynamic analysis suitable for any structure.