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Suhail Gul

Eccentricity Values In Etabs

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What should i put eccentriccity values in EQX-eccy and EQY-eccx?

5% of building dimesnion perendicular to the direction of seismic load is default. However, code requires engineers to check to trosional irregularity, which if found requires the default eccentricity (5%) to be increased.

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Dear rummaan17,

Step 1: Include 5% eccentricity in X and Y cases (X+Eccen Y, X-Eccen Y, Y+Eccen X, Y-Eccen X). Total 4 cases.

Step 2: Check if torsional irregularity exists. If yes then increase 5% values to the amplified values (7%, 8% whatever, There is upper limit too in the code).

This increase of eccentricity would be different for each floor plate and can be manually entered into ETABS by using "override diaphragm eccentricities" option.

You should do this for all the 4 cases.

Now after doing this, if you torsional irregularity still exists, you don't need to further iterate. Only one time increase is sufficient.

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Dear Mr.Rana, Thanks for your response.
I just want to know in which case need to check the torsional irregularity ratio ?.

I mean to check it in EQX and EQY only and then amplify the eccentricity in  (X+Eccen Y, X-Eccen Y, Y+Eccen X, Y-Eccen X) . Am i right ??

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On 11/7/2016 at 5:55 AM, rummaan17 said:

Dear Umar,

We should check the buidling drift ratio only in EQX and EQY right ? Not the one with eccentricity ?

You should include accidental torsion when computing drift. Read my response here:

Thanks.

 

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