Earthquake Analysis / Dynamic Analysis / Seismic Analysis based on ASCE 7-16
Following steps are involved :
Determination of Maximum considered earthquake (MCE) spectral response accelerations for short period (0.2s) called Ss and for long period (1 s) S1 using maps issued by IBC. Structure can be assigned the Seismic Design Category (SDC) A if Ss≤0.15 and S1≤0.04.
Site class is to be selected from A-F in accordance to guidelines present in ASCE. IF sufficient data is not present than site class D can be assigned . Moreover for problematic soils site class E & F could be assigned.
Calculation of MCE spectral response accelerations adjusted for site class as given below
[Where Fa & Fv are site coefficients selected from IBC table.]
Calculation of damped spectral response accelerations at short and long period .
Determination of Risk Category out of 1-4 from IBC table and Importance Factor is than selected based on risk category selected . [If risk category 1-3 & S1≥0.75 than SDC “E” will be assigned , if If risk category 4 and S1≥0.75 than than SDC “F” will be assigned]. Finally SDC is selected based on the values of Risk Category and SDS and SD1 . For Seismic Design Category “A-E” , we have to use SDS , SD1 and Risk category for selection of appropriate SDC.
Specify the Structure peak height “hn” and number of stories “N”.
Finally select the response modification coefficient “R” , System over strength parameter “Ω” and deflection amplification factor.
Structural Analysis methods can only be the ones listed in ASCE 7-22 based on the structural system and SDC. There are three methods available: (a)Equivalent Lateral Force (b) Modal Response Spectrum (c)Seismic Response History
Equivalent Lateral Force :
i- Main thing is to calculate the Base shear, given by the formula :V= CsW
Cs=Seismic response coefficient & W=Effective seismic weight
ii-The second aspect to calculate the vertical distribution / story shear
iii- Lastly we have to calculate the story drift.