Seismosoft | Earthquake Engineering Solutions

Dear all,
i work on MDOF and SDOF inelastic demands comparison for a constant ductility. So i developed a code which changes the ground motion scale factor to reach target ductility for MDOF. Also i developed equivalent SDOF system with same period and mass to MDOF. Also i developed a code in Matlab to calculate yield strength (I means yeild stress of steel material) of SDOF to limit demand ductility to predefined MDOF ductility. to do this i run nonlinear time history analysis to capture Dmax. Dy is also calculated by bi linear idealization of pushover curve for SDOF. in SDOF i choose Fy=2400 kfg/cm2. to reach the target ductility in SDOF i change Fy of SDOF in each iteration. But after all when i divided Vmdof to Vsdof, the ratio became less than 1 that i think is not correct due to higher mode effects. I want to know is the method i select to achieve target ductility is true? i means for constant ground motion scale factor, changing the Fy of material for SDOF is a Logical way? and What is the seismosignal methodology to reach constant ductility for SDOF?.

Dear n_siahpolo,

I must confess that I am not sure I fully understand your query (or, perhaps better, queries), given that in your one paragraph you refer to two different issues: constant-ductility spectra and MDOF-to-SDOF transformations.

In any case, answering to your final question, SeismoSignal does derive constant-ductility spectrum in the manner that you describe, which is also aligned with what others propose (if you google the expression "constant-ductility response spectra", you will find presentations/publications detailing the very same steps that you listed in your post).

Best,

Rui

For the SeismoSoft team, I wonder if you could elaborate just a bit on the hysteretic model adopted in SeismoSignal. It is described as an "elasto-plastic representation of the system" in the excellent help file. My question regards the unloading behavior of the model in SeismoSignal: does the program mimic behavior using 'bl_kin' or 'bl_sym' hysteretic models, to use SeismoStruct terminology (I suspect that it is the 'bl_kin' model, but am not certain). Thanks very much.

Indeed Tim, it is similar to the SeismoStruct 'bl_kin' model
Regards,
Seismosoft Support