2024
Torsion Irregularity
FADY ADEL
Torsion Irregularity
Fady Adel
1|Page
HOW TO CHECK TORSION IN ETABS
Go to View > Display Table>Analysis Results>Joint Output>Displacements>Story
Max Over Avg Displacement
Fady Adel
2|Page
The Story Max Over Avg dispacement Table below shows the displacement Ratio. The
amplification factor should be considered on the corresponding level whenever there is ratio
exceeding 1.20.
But when you use (SX) use direction X & when you use (SY) use direction Y
Fady Adel
3|Page
If Ratio > 1.2 we will calculate Amplification Factor for these stories
Fady Adel
4|Page
2. Calculation of Torsional Amplification Factor, Ax.
After confirming the presence of a torsional irregularity, we will then calculate the torsional
amplification factor, Ax, using the equation provided by the ASCE 7-16 code
Note that the above Ax, shall not be less than 1.0 and its not required to exceed by
where:
δmax: Maximun displacement values taken from ETABS Analysis results.
δavg: Average displacement values taken from ETABS Analysis results.
Fady Adel
5|Page
Extract the above table to Excel to calculate the Ax in each floor level and Amplified
Eccentricity as follows:
TABLE: Story Max Over Avg Displacements
A
old
New
ECCENTRICITY
Output
(m)
Story
Direction Maximum Average Ratio =(max/1.2av)^2 eccentricty eccentricity LY
Case
=(ratio/1.2)^2
(0.05)
=A * .05
=A*.05*LY
mm
mm
Upper Roof
SX
X
35.274
31.989 1.103 0.844867361
0.05
0.04224337 7.35 0.310488755
Roof
SX
X
58.943
42.327 1.393 1.347534028
0.05
0.0673767 21 1.414910729
Third
SX
X
53.146
37.284 1.425 1.41015625
0.05
0.07050781 21 1.480664063
Second
SX
X
45.636
31.305 1.458
1.476225
0.05
0.07381125 21
1.55003625
First
SX
X
37.047
24.734 1.498 1.558336111
0.05
0.07791681 21 1.636252917
Ground
SX
X
24.509
15.648 1.566
1.703025
0.05
0.08515125 18
1.5327225
Basement 1 SX
X
12.308
7.318 1.682 1.964669444
0.05
0.09823347 18
1.7682025
TABLE: Story Max Over Avg Displacements
Output
Story
Case Type Direction Maximum Average
Case
mm
mm
Upper Roof
SY LinRespSpec
Y
34.999
32.694
Roof
SY LinRespSpec
Y
44.265
35.955
Third
SY LinRespSpec
Y
39.98
31.813
Second
SY LinRespSpec
Y
34.341
26.776
First
SY LinRespSpec
Y
27.781
21.133
Ground
SY LinRespSpec
Y
18.163
13.193
Basement 1 SY LinRespSpec
Y
9.171
6.103
A
old
New
ECCENTRICIT
Y (m)
Ratio =(max/1.2av)^2 eccentricty eccentricity LX
=(ratio/1.2)^2
(0.05)
=A * .05
=A*.05*LX
1.071
1.231
1.257
1.283
1.315
1.377
1.503
0.79655625
1.052334028
1.09725625
1.143117361
1.200850694
1.31675625
1.56875625
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.03982781 8.5 0.338536406
0.0526167 25.5 1.341725885
0.05486281 25.5 1.399001719
0.05715587 25.5 1.457474635
0.06004253 25.5 1.531084635
0.06583781 25.5 1.678864219
0.07843781 25.5 2.000164219
The eccentricity length to consider is the perpendicular dimension to the direction of force in
consideration.
If use (Sx) use Ly and iy (Sy) use Lx
Fady Adel
6|Page
Two Methods on how to Apply the Effect of torsional
irregularity in our model.
Method 1:
Calculate the new eccentricity values by multiplying the eccentricity length with the amplified
eccentricity factor. In load case
Fady Adel
7|Page
Fady Adel
8|Page
Method 2:
we have to calculate only the maximum new eccentricity only
from table above max new eccentricity for case sx=.098
Do The Same for SY
Fady Adel
9|Page
0
