Base shear scaling

[tony.ridley]

Hi,

When scaling base shear in seismic analysis, I thought that the seismic analysis should be scaled (for example X direction) according to the reaction in X direction from the MAIN CONTRIBUTING MODE, not the CQC total reaction.  

It seems Robot adjusts base shear based on CQC combination value.  

Can anyone please clarify which reaction (main mode or CQC total) I should be scaling base shear to hit?

Tony

[tony.ridley]

bump

[Pawel.Pulak · Accepted solution]

Hi Tony,

one of the reasons why Robot adjusts base shear based on CQC combination value is that in many cases of irregular and low structures there are no modes with mass participation higher than 30%.

In such situations it is even difficult to distinguish main contributing mode.

Scaling CQC combination seems the approach close to scaling total seismic action and applicable independently from properties of specific structures.

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