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The majority of damping for a massive foundation block would be from radial or geometric damping provided by the surrounding soil. The effect of material damping within the foundation block itself would likely be much smaller than that of geometric damping.
When modeling soil-structure interaction with a single link object, the damping assigned on the Linear Link/Support Directional Properties menu should represent radial damping, as described in Wilson 2004, and given in units of Force-Sec/Length (Force/Velocity).
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The
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damping
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value
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specified
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through
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Analysis
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Case
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Data
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>
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Linear
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Modal
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History
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should
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represent
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the
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material
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or
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structural
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damping
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inherent
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to
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the
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foundation
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system
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itself.
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References
Wilson,
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E.
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L.
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(2004).
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Static
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and
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Dynamic
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Analysis
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of
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Structures
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(4th
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ed.,
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pp.
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197).
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Berkeley,
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CA:
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Computers
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and
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Structures,
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Inc.
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Available for
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purchase
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on
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