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Damping Recommendation from ATC 72

Posted: 04 Jan 2019, 16:59
by Kirkaguel
ATC 72 is the guideline used for tall building design using Performance Based Design approach in the USA and this guideline has been referenced by PEER TBI 2017, LATBSDC 2017 and CTUBH 2017 and it discusses a very detailed review of the damping effect in a structure. Section 2.4 of the guideline discusses issues and different methods of damping i.e. Rayleigh damping and Modal Damping. One of the recommendations is to use Modal Damping.

Perhaps it would help if this will be reviewed by seismosoft team so that Modal Damping could be incorporated in future releases of Seismostruct.

I am attaching a copy of ATC 72 here ... report.pdf


Re: Damping Recommendation from ATC 72

Posted: 05 Jan 2019, 16:59
by huffte
Hi Kirkaguel. Interesting topic. I wonder if the recommendation for modal damping is still valid given that the current Seismostruct includes the option to develop damping based on tangent stiffness where the damping matrix is updated as discussed in ATC 72.

Regarding nonlinear analysis, Article 2.4.5 reads: 'Among the various alternatives, it is generally recommended to model viscous damping using modal damping, Rayleigh damping, or a combination of the two.' I certainly support the Seismosoft team should they decide to incorporate the option for modal damping. It just seems that care is warranted in making any suggestion that modal damping is the superior option.

The 'Damping' topic in the Seismostruct help file has a very good discussion on the subject which is highly recommended reading for all users.

Re: Damping Recommendation from ATC 72

Posted: 05 Jan 2019, 18:30
by Kirkaguel
Dear Hufttie, the suggestion that modal damping is a superior option was taken from the research of Dr. Powell who happens to be the original developer of the Perform 3D software. In one of his presentation he suggested that the most reliable damping method is a combination of modal damping with minimum value of rayleigh damping. It will give reliable results of damping at lower to higher mode.

I am attaching a screenshot of one PBD seminars done by PEER which they show the part of the paper done by Dr. Powell.

Re: Damping Recommendation from ATC 72

Posted: 05 Jan 2019, 18:46
by Kirkaguel
Dr. Powell has also discussed the damping topic on his Performance Based Design seminar here ... 3322dSqrls

the damping topic starts at 40 minutes

Re: Damping Recommendation from ATC 72

Posted: 06 Jan 2019, 08:56
by seismosoft
Thank you for your suggestion, which we will consider for one of the future releases of the program.
Seismosoft Support

Re: Damping Recommendation from ATC 72

Posted: 06 Jan 2019, 16:10
by ruipinho

Just a quick note to support the (always wise) comments of huffte; there is no such thing as A correct or superior equivalent viscous damping model option.

Indeed, if you do a thorough literature review on the subject, you will quickly realise that over the past 20 years many different proposals on the subject have been made by a number of very experienced and knowledgeable researchers or research teams.

Those different approaches all have their pros and cons, and the important thing is for users to be well aware of the limitations of whatever modelling they are adopting, and thus employ it with due care and judgement.

In other words, even if Seismosoft does implement in SeismoStruct the possibility of users employing Modal Damping in their analyses, that should not necessarily be interpreted as a statement that Modal Damping is a superior or always-recommended option, but rather as a supplying of additional modelling flexibility to experienced and judicious modellers.