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# drift of torsional irregular structure

## drift of torsional irregular structure

(OP)
HI,

In a torsional structure, the displacement resulting from the lateral seismic analysis will give rise to displacements in the 2 directions ( X and Y).
when comparing the story drift to the allowable one, each direction is to be compared separately to the allowable code limit or the vector of the coupled displacements is to be considered?
same question for base shear scaling.

Thank you

(OP)
Any input?

### RE: drift of torsional irregular structure

For each direction of applied loading that you consider, you would undertake the drift estimate in that direction shown below. The sketch does a pretty good job so I'll not elaborate further unless you have further questions. In the sketch below, dA & dB are shown in the same sense as the applied load.

### RE: drift of torsional irregular structure

(OP)
Same applies for base shear scaling. U would scale the static base shear versus the dynamic one for each direction even there is a component in the other direction right ?

### RE: drift of torsional irregular structure

Yes, you check each direction individually, not the vector.

Note that for a torsionally irregular structure you need to compare the MAX deflection to the allowable, not the average (story).

from ASCE 12.8.6
For structures assigned to Seismic Design Category C, D, E, or F having horizontal irregularity Type 1a or 1b of Table 12.3-1, the design story drift, Δ, shall be computed as the largest difference of the deflections of vertically aligned points at the top and bottom of the story under consideration along any of the edges of the structure.

### RE: drift of torsional irregular structure

(OP)
Ok thank you larryhd
I think same thing applies for base shear scaling right?
Base shear should be compared per direction even if the dynamic shear reveals a high value in the other direction.
Thank you

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