Estimation of hysteretic soil damping from laboratory measurements including strain accumulation
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Date
2014-05-12Metadata
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- NGI report [179]
Abstract
The periodic forces due to wind, surface waves and swells on offshore installations
such as offshore wind turbines lead to cyclic motion of the soil foundation. The
damping properties of soils account for a part of the energy dissipation of the
Offshore Wind Turbine (OWT) system. Understanding damping is therefore
important with respect to the structural response and the cost-effective design of
structures. Unfortunately, OWT foundation damping is sparsely studied, and the
understanding of this parameter is therefore limited. The present results provide a
step forwards towards a better understanding and interpretation of stiffness and
damping parameters of soils, and focuses on basic concepts and on the effect of
permanent strain accumulation in particular. Analyses of laboratory data have
shown that the interpreted hysteretic soil damping becomes too large unless the
permanent strain accumulation is filtered out. On the other hand, the strain
accumulation contributes to hysteretic loss in addition to the material damping. The
current study is a first step towards a better understanding and interpretation of
damping parameters for soils, and focuses on basic concepts. A crucial next step
would include methods for interpreting the damping correctly in models soilstructure
interaction for realistic loads and structures, to clarify the importance of
soil damping for offshore wind turbine foundations. Due to the industry’s need for
simple and efficient models used for large scale, it is essential that the damping
formulation is kept simple.