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# How to calculate story drift for response spectra analysis?

## How to calculate story drift for response spectra analysis?

(OP)
When perform reponse spectra load case in X direction, there is always some forces in Y direction. Sometimes the forces in Y direction is pretty large or even close to force in X direction. Therefore the drift in Y direction is close to the drift in X direction.

So how to check the story drift? Just check drift in X direction by neglecting drift in Y direction or use squre root of the sum of suqres of X and Y directions?

Thanks
Replies continue below

### RE: How to calculate story drift for response spectra analysis?

I assume that you are designing your structure using a force-based seismic design. If that is the case, how are you designing your structure, are you calculating your drift for the x and y-direction respectivly or are you modelling by x and y simutaneously. In the latter case, you will need to model 100% loading in one direction coincidental with 30% orthogonal loading.

### RE: How to calculate story drift for response spectra analysis?

i think that you dont need to do the sum of sq roots of the two values ,but just check that the drifts values you getting in both x and y directions for same case and they should satisfy the limit set by Code you following.

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