Dear researchers
What is your opinion about the criterion recommended in seismic codes for determining scaling period, which are used to scale ground motion records?
As you know, the mentioned criterion is the period of the structure’s dominant mode, which has the largest modal participating mass ratio (usually the first vibration mode). Hence, the period of the mode with the second largest modal participating mass ratio is not considered in the scaling process. Consequently, although this criterion usually results in the largest value of scaling period, it is not logical ones.
This is especially important when Tuned Mass damper (TMD) or Base-Isolation system is utilized, which cause the modal properties of the structures to change.
I used a new criterion based on the weighted mean value of the periods for the structures equipped with TMD.
Have you used any criteria other than the criterion mentioned in the seismic codes?
Dear Majid,
The criterion I use follows the general recommendations of the Italian Building Code, which simply suggests to scale the ground motions in the period range deemed significative, and not a single one.
The choice of a single or multiple periods is useful when using the Conditional Mean Spectrum as the target. The periods can be based on a modal analysis or general considerations about the structure behavior, as you mentioned.
Baker (https://web.stanford.edu/~bakerjw/research/conditional_spectrum.html) deals with the choice of the scaling period in several of his papers.
More recently, Kwong and Chopra suggested a new methodology to select and scale ground motionsConference Paper The CMS-UHS Composite Spectrum for intensity-based assessmen...
Since this is a research in progress, I expect to find many different recommendations depending on the country seismic code.
Gianluca
Dear Gianluca Regina
I know that a period range deemed significative is recommended in seismic codes which are usually in the period range of 0.2T to 1.5T. I am talking about the mentioned T, that usually is the structure’s dominant mode.
Dear Majid,
the only criteria for chosing the period T that I know of are the ones that I mentioned before. As you said, the structure's dominant period is not always the best choice.
The latest criteria proposed by Kwong and Chopra seem pretty logical to me, and they are not present in seismic code (as far as I know).
I do not expect to see one general criterium for the choice of T in seismic codes any time soon.
Dear Majid Tavakolinia,
I am not fully agree with the approach to use the weighted mean value of the periods for the structures equipped with TMD. Are you speaking about single mass damper? In my research I came to conclusion that three-mass damper is much more effective than single mass damper (please see my paper:
Experimental Investigation of Efficiency of Tuned Single and Double Mass Damper and its Application in the Form of an Additional Upper Floor for Seismic Protection of Existing Multistory Buildings via the ResearchGate network). Therefore, you have to be very careful by manipulating with the values of period not only for buildings with TMD but also for the base isolated buildings. And a special attention needs to be payed to the base isolated buildings equipped with the dynamic dampers at the level of isolation system (please see my other paper: The State of the Art in Structural Control in Armenia and Proposal on Application of the Dynamic Dampers for Seismically Isolated Buildings).
Prof. Mikayel Melkumyan
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