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Damping in the platform models for soil-structure interaction problems: Rayleigh damping options and limitations in modal analysis

Damping in the platform models for soil-structure interaction problems: Rayleigh damping options... AbstractModal approach is widely used in seismic analysis. Moreover, spectral theory used in seismic codes all over the world is based on this modal approach. However, modal approach has an implicit limitation – relatively small or homogeneous damping. Otherwise the equations of motion in the ‘main coordinates’ remain coupled through the damping matrix even after decoupling through inertia and stiffness matrices. Due to this coupling, the results obtained using decoupled 1D modal equations of motion are incorrect. Practical example of such a situation is a platform model of the soil-structure system used for the analysis of soil-structure interaction (SSI) controlling seismic response of main NPP structures. Here, we see considerable damping in the ‘soil’ dashpots, completely different from structural damping. The difficulty with modal damping in SSI problems was realized in 1970s, and several suggestions have been made in order to save conventional modal approach. The author discusses these suggestions using a very simple 1D model and proposes to address the difficulties using combined asymptotic method (CAM). In CAM, a new platform model with homogeneous damping is analysed (thus enabling modal approach), and the difference between ‘true’ damping and artificial ‘platform’ damping is accounted for in the modified platform excitation. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Structural Integrity and Maintenance Taylor & Francis

Damping in the platform models for soil-structure interaction problems: Rayleigh damping options and limitations in modal analysis

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Damping in the platform models for soil-structure interaction problems: Rayleigh damping options and limitations in modal analysis

Abstract

AbstractModal approach is widely used in seismic analysis. Moreover, spectral theory used in seismic codes all over the world is based on this modal approach. However, modal approach has an implicit limitation – relatively small or homogeneous damping. Otherwise the equations of motion in the ‘main coordinates’ remain coupled through the damping matrix even after decoupling through inertia and stiffness matrices. Due to this coupling, the results obtained using decoupled 1D...
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Publisher
Taylor & Francis
Copyright
© 2016 Korea Institute for Structural Maintenance and Inspection
ISSN
2470-5322
eISSN
2470-5314
DOI
10.1080/24705314.2016.1211237
Publisher site
See Article on Publisher Site

Abstract

AbstractModal approach is widely used in seismic analysis. Moreover, spectral theory used in seismic codes all over the world is based on this modal approach. However, modal approach has an implicit limitation – relatively small or homogeneous damping. Otherwise the equations of motion in the ‘main coordinates’ remain coupled through the damping matrix even after decoupling through inertia and stiffness matrices. Due to this coupling, the results obtained using decoupled 1D modal equations of motion are incorrect. Practical example of such a situation is a platform model of the soil-structure system used for the analysis of soil-structure interaction (SSI) controlling seismic response of main NPP structures. Here, we see considerable damping in the ‘soil’ dashpots, completely different from structural damping. The difficulty with modal damping in SSI problems was realized in 1970s, and several suggestions have been made in order to save conventional modal approach. The author discusses these suggestions using a very simple 1D model and proposes to address the difficulties using combined asymptotic method (CAM). In CAM, a new platform model with homogeneous damping is analysed (thus enabling modal approach), and the difference between ‘true’ damping and artificial ‘platform’ damping is accounted for in the modified platform excitation.

Journal

Journal of Structural Integrity and Maintenance – Taylor & Francis

Published: Jul 2, 2016

Keywords: Soil-structure interaction; frequency domain; soil springs and dashpots; platform model

References

  • Combined asymptotic method for soil-structure interaction analysis