Median response spectra was obtained from site response analyses (SHAKE) of soil sites using recorded earthquakes. I have classified the soil sites into different site categories and I need to define design response spectrum similar with that of Eurocode-8. I can find the spectrum intensities of soil (Isoil) and rock sites (Irock) to calculated S, but I am confused how I can derive the SR, which represents the contribution due to change in shape of rock and soil spectra when they are constrained to have the same ordinate at zero period.
Equation: Isoil/Irock = S *SR
Dear Satish
According to your description, you had some earthquake records that some them have been recorded by the seismic stations located on rock site and the other ones on soil site. Please make sure that you have categorized the sites correctly. You should use Vs30 parameter to do that. (Vs30=30/(d1/vs1+d2/vs2...dn/vsn); where d is the thickness of the soil layers, vs is the shear wave velocity of each layer, d1+d2+...+dn=30m).
In addition, please make sure that the earthquake records have been filtered in both North-South (NS) and East-West (EW) directions and they have no any noise.
Then, when you calculate the response spectra due to the earthquake records, you should have two spectra due to each record. One for NS direction and one for EW direction. Then, you should calculate geometric or arithmetic mean of these two spectra. In final, you may have for example 50 spectra due to the earthquake records on rock site and 50 spectra due to records on soil site.
After that, you should calculate the average+1 standard deviation (sd) value of the 50 response spectra obtained for rock site and also the average+1 standard deviation (sd) of the 50 spectra obtained for soil site. Then as you mentioned also you may find the S factor by dividing the two ordinates (i.e., rock and soil) at zero period.
If you use response spectra, better use the tri-logaritmic graphic representation. The T changing point in the conventional, linearized response spectra of EC8 are referred to the part at constant acceleration, velocity and displacement respectively.
- Badges
- Science topic
- Similar topics
- Engineering
- Modeling