NEHRP Clearinghouse
- Title
- Conservatism in Summation Rules for Closely Spaced Modes.
- File
- PB301328.pdf
- Author(s)
- Kelly, J. M.; Sackman, J. L.
- Source
- May 1979, 35 p.
- Identifying Number(s)
- UCB/EERC-79/11
- Abstract
- It is shown that the method recommended by the Nuclear Regulatory Commission to be used to combine spectral response in the case of closely spaced modes arise in structures from symmetry and where there is a light appendage with a frequency close to one of the natural frequencies of the structure. The approach proposed here is that the modes that are not closely spaced be treated by modal analysis and the closely spaced modes, in the case of two closely spaced modes, be treated as a coupled two-degree-of-freedom system. If this is done, the beat phenomenon, the most important characteristic of the interaction between the two closely spaced modes, is evident, as is the associated result that the peak response of the coupled system is developed much later than the peak responses obtained in the individual modes by standard analysis.
- Keywords
- Oscillation modes; Vibration; Spectral response; Dynamic response; Nuclear reactor safety; Earthquakes; Dynamic structural analysis