Autodesk Robot Structural Analysis

[#1]

Hi guys,

• If I include damping in modal case that precedes the Spectral case, do I need to add a value for damping in the spectral definition?   If I include damping in the spectral definition and also check on damping in modal, does Robot "double up" on damping?

• In the AS1170 seismic, there is no damping definition.  Do I need to check it on in Modal definition for it to be included?

Tony

[#2]

Hi Tony,

some summary on using damping in  modal, spectral and seismic cases.

Damping defined in advanced parameters of modal case

 is used in:

1/ damping correction of elastic spectra in these seismic codes where it is possible - for instance in EN-1998-1-1 (Eurocode 8)

2/ in calculation of complete quadratic combinations (CQC) and double sum method (2SM) combinations - see appropriate Help topic

Damping defined in spectral analysis is not used directly in spectral analysis calculations- it can be treated as some identifier of various spectra here. It is used  when preparing spectra in case of spectra interpolation:

Above settings correspond to different actions so there is no risk to consider damping "twice".

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Regards,

[#3]

Hi Pawel thanks for your reply.  What about this damping setting:

[#4]

This damping setting would be used only when using this spectra in Spectra Interpolation:

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Regards,

[#5 · Accepted solution]

Thanks for your reply Pawel,

Perhaps the dialogue box should be removed from it's current position, it's a bit misleading. 

Thanks anyway,

Tony

[#6]

Hi Tony,

sorry for incomplete/incorrect answer in my previous post:

damping from properties of spectra is used in spectra averaging not only in spectra definion but also when using averaged spectra directly in spectral load case - see the screen capture below:

In such case the actual relative damping used to calculate averaged spectra will be taken from advanced parameters of modal case preceding this spectral case.

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If this post answers your question please click "Accept as Solution". It will help everyone to find answer more quickly!

Regards,