I need to perform a nonlinear Time History analysis on 7 ground motions. How do I apply the scale factor so that these ground motions are scaled to PGA like 0.1g, 0.2g. I am using PEER ground motion database wherein the acceleration time history data is "in units of g"
I would do it manually in an Excel sheet, and then apply the scaled ground motions on SAP2000. you just multiply your time histories by SF= PGA,target/PGA,recorded. (the target is the design spectrum, it depends on the location and the soil type)
PGA is the maximum acceleration in your time histories. You don't have to convert them to ground spectrum.
The steps followed for the simplified method by direct scaling of records w.r.t. [Sa(T1,5%)] is as follows:
1. Modal analysis is executed in software to determine the fundamental time period T1 for the first mode of building.
2. From the unscaled response spectrum for selected ground motion chosen from the PEER Centre database, spectral acceleration is determined corresponding to T1.
3. The scale factor is determined as, Scale Factor = 1/Sa(T1) which is used to obtain normalized response spectrum.
4. This scale factor is multiplied by the acceleration due to gravity i.e. ‘g’ to determine normalized time history.
5. Then obtained scale factor is multiplied with the selected increments i.e. 0.1, 0.2,….., etc.
6. These new scale factors are used in each direct integration time-history load case.
in the load case, choose time history and then you get the command scale factor by which you can scale the accelerograms according to the desired value of PGA.
Punashri Prakash Phadnis Ma'am, how this procedure will be applied in case I have Time History (TH) (Unscaled) and a known Response spectrum. I want to scale the TH to Match the Response Spectrum (RSP). Can you please elaborate. Gone the through the Pdf. The obtained Scale Factors need to be multiplied to TH acceleration?
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