# V. IS 1893 2016 Torsion Irregularity

Verify part 1 of the torsional irregularity check per the IS 1893 2016 Part 1 specifications.

## Details

A three story building is modelled with floor diaphragms defined at each floor level.

A 1 kip (4.4482 kN) load is applied to each diaphragm in both the global X and Z directions. In STAAD.Pro, this is modelled using an analytical node in each diaphragm. This is used to obtain the displacements in the nodes of the diaphragm.

### Structure diagram

Nodes 17, 18, and 19 are the control nodes in each diaphragm.

## Validation

As per Cl. 7.8.2, the design eccentricity, edi, is computed as the a constant times the dynamic eccentricity plus or minus the accidental eccentricity:

$edi=|1.5esi+0.05bi(Case 1)1.0esi−0.05bi(Case 2)$
where
 esi = the static eccentricity at floor i, which is the distance between the center of rigidity and the center of mass at that level bi = the floor plan dimension at floor i, perpendicular to the direction of force = 5 m for this example in both direction at all floors

Also, to perform a torsion irregularity check unit load should be applied at edi considering design eccentricity. Hence, in addition to unit load F = 1 kip (4.45 kN), a moment M = F × (lever arm) is also applied at the center of mass.

The displacements induced because of the applied loads on the control nodes for the nodes situated on the extremities of each diaphragm is taken from the STAAD.Pro output for each lateral direction.

X direction

By inspection, the center of rigidity (as reported by STAAD.Pro) and the center of mass are located at the same point at each floor. Therefore, esi = 0.

Table 1. X Direction: Case 1 (ACC = +0.05, DEC = 1.5)
Diaphragm Control Node esi (m) (C.M. - C.R.) Dynamic Eccentricity (1.5esi) Accidental Eccentricity (0.05bi) Design Eccentricity

(e di = 1.5esi+0.05bi)

Fx Applied at C.M. My Applied at CM

(Fx×(edi-esi)

1 17 0 0 0.25 0.25 4.45 1.11
2 18 0 0 0.25 0.25 4.45 1.11
3 19 0 0 0.25 0.25 4.45 1.11
Table 2. X Direction: Case 2 (ACC = -0.05, DEC = 1.0)
Diaphragm Control Node esi (m) (C.M. - C.R.) Dynamic Eccentricity (1.0esi) Accidental Eccentricity (-0.05bi) Design Eccentricity

(e di = 1.0esi-0.05bi)

Fx Applied at C.M. My Applied at CM

(Fx×(edi-esi)

1 17 0 0 -0.25 -0.25 4.45 -1.11
2 18 0 0 -0.25 -0.25 4.45 -1.11
3 19 0 0 -0.25 -0.25 4.45 -1.11

The displacements induced because of the applied loads centers of mass for the nodes situated on the extremities of each diaphragm are taken from the STAAD.Pro output for each lateral direction.

Table 3. X Direction: Case 1 Checks
Diaphragm Control Node Primary LC Number Diaphragm Extremities Displacements (mm) Δmax/Δavg Status
Extreme Node 1 Extreme Node 2 Δx Extreme Node 1 Δx Extreme Node 2 Δx Average
1 17 1 2 or 3 6 or 7 0.466 0.498 0.482 1.033 PASS
2 18 2 9 or 10 11 or 12 2.399 2.487 2.443 1.018 PASS
3 19 3 13 or 14 15 or 16 6.016 6.164 6.090 1.012 PASS
Table 4. X Direction: Case 2 Checks
Diaphragm Control Node Primary LC Number Diaphragm Extremities Displacements (mm) Δmax/Δavg Status
Extreme Node 1 Extreme Node 2 Δx Extreme Node 1 Δx Extreme Node 2 Δx Average
1 17 4 2 or 3 6 or 7 0.498 0.466 0.482 1.033 PASS
2 18 5 9 or 10 11 or 12 2.487 2.399 2.443 1.018 PASS
3 19 6 13 or 14 15 or 16 6.164 6.016 6.090 1.012 PASS

Z direction checks

Table 5. Z Direction: Case 1 (ACC = +0.05, DEC = 1.5)
Diaphragm Control Node C.R. (from output file) esi (m) (C.M. - C.R.) Dynamic Eccentricity (1.5esi) Accidental Eccentricity (0.05bi) Design Eccentricity

(e di = 1.5esi+0.05bi)

Fx Applied at C.M. My Applied at CM

(Fx×(edi-esi)

1 17 0.247 1.239 - 0.247 = 0.992 1.488 0.25 1.738 4.45 3.32
2 18 0.319 1.239 - 0.319 = 0.92 1.380 0.25 1.630 4.45 3.16
3 19 0.372 1.313 - 0.372 = 0.941 1.412 0.25 1.662 4.45 3.20
Table 6. Z Direction: Case 2 (ACC = -0.05, DEC = 1.0)
Diaphragm Control Node C.R. (from output file) esi (m) (C.M. - C.R.) Dynamic Eccentricity (1.0esi) Accidental Eccentricity (-0.05bi) Design Eccentricity

(e di = 1.0esi-0.05bi)

Fx Applied at C.M. My Applied at CM

(Fx×(edi-esi)

1 17 0.247 1.239 - 0.247 = 0.992 0.992 -0.25 0.742 4.45 -1.11
2 18 0.319 1.239 - 0.319 = 0.92 0.920 -0.25 0.670 4.45 -1.11
3 19 0.372 1.313 - 0.372 = 0.941 0.941 -0.25 0.691 4.45 -1.11
Table 7. Z Direction: Case 1 Checks
Diaphragm Control Node Primary LC Number Diaphragm Extremities Displacements (mm) Δmax/Δavg Status
Extreme Node 1 Extreme Node 2 Δz Extreme Node 1 Δz Extreme Node 2 Δz average
1 17 7 2 or 6 3 or 7 0.238 0.27 0.254 1.063 PASS
2 18 8 9 or 11 10 or 12 0.935 1.009 0.972 1.038 PASS
3 19 9 13 or 15 14 or 16 1.916 2.046 1.981 1.033 PASS
Table 8. Z Direction: Case 2 Checks
Diaphragm Control Node Primary LC Number Diaphragm Extremities Displacements (mm) Δmax/Δavg Status
Extreme Node 1 Extreme Node 2 Δz Extreme Node 1 Δz Extreme Node 2 Δz average
1 17 10 2 or 6 3 or 7 0.232 0.392 0.312 1.256 WARNING
2 18 11 9 or 11 10 or 12 0.913 1.325 1.119 1.184 PASS
3 19 12 13 or 15 14 or 16 1.873 2.578 2.226 1.158 PASS

## Results

Table 9. Comparison of results (max/min displacement ratios and check results)
X Direction; Case 1 1 PASS (1.033) PASS (1.0333) negligible
2 PASS (1.018) PASS (1.0180) negligible
3 PASS (1.012) PASS (1.0122) negligible
X Direction; Case 2 1 PASS (1.033) PASS (1.0333) negligible
2 PASS (1.018) PASS (1.0180) negligible
3 PASS (1.012) PASS (1.0122) negligible
Z Direction; Case 1 1 PASS (1.063) PASS (1.0622) negligible
2 PASS (1.038) PASS (1.0381) negligible
3 PASS (1.033) PASS (1.0329) negligible
Z Direction; Case 2 1 WARNING (1.256) WARNING (1.2562) negligible
2 PASS (1.184) PASS (1.1841) negligible
3 PASS (1.158) PASS (1.1584) negligible

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\06 Loading\IS 1893\IS 1893 2016 Torsion Irregularity.STD is typically installed with the program.

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 05-Mar-19
END JOB INFORMATION
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 0; 2 0 5 0; 3 5 5 0; 4 5 0 0; 5 0 0 5; 6 0 5 5; 7 5 5 5; 8 5 0 5;
9 0 10 0; 10 5 10 0; 11 0 10 5; 12 5 10 5; 13 0 15 0; 14 5 15 0; 15 0 15 5;
16 5 15 5; 17 1.239 5 2.5; 18 1.239 10 2.5; 19 1.313 15 2.5
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4; 4 2 6; 5 3 7; 6 5 6; 7 6 7; 8 7 8; 9 2 9; 10 3 10;
11 6 11; 12 7 12; 13 9 10; 14 9 11; 15 10 12; 16 11 12; 17 9 13; 18 10 14;
19 11 15; 20 12 16; 21 13 14; 22 13 15; 23 14 16; 24 15 16;
DEFINE MATERIAL START
ISOTROPIC CONCRETE
E 2.17185e+07
POISSON 0.17
DENSITY 23.5616
ALPHA 1e-05
DAMP 0.05
TYPE CONCRETE
STRENGTH FCU 27579
END DEFINE MATERIAL
MEMBER PROPERTY AMERICAN
2 3 5 7 8 10 12 13 15 16 18 20 21 23 24 PRIS YD 0.35 ZD 0.25
MEMBER PROPERTY AMERICAN
1 4 6 9 11 14 17 19 22 PRIS YD 0.5 ZD 0.65
CONSTANTS
MATERIAL CONCRETE ALL
SUPPORTS
1 4 5 8 FIXED
*MEMBER CRACKED CODE IS1893 2016
*1 3 6 8 TO 12 17 TO 20 REDUCTION RIY 0.7 RIZ 0.7
*2 4 5 7 13 TO 16 21 TO 24 REDUCTION RIY 0.35 RIZ 0.35
MEMBER CRACKED
1 3 6 8 TO 12 17 TO 20 REDUCTION RIY 0.7 RIZ 0.7
2 4 5 7 13 TO 16 21 TO 24 REDUCTION RIY 0.35 RIZ 0.35
SELFWEIGHT X 1
SELFWEIGHT Y 1
SELFWEIGHT Z 1
FLOOR DIAPHRAGM
DIA 1 TYPE RIG HEI 5
DIA 2 TYPE RIG HEI 10
DIA 3 TYPE RIG HEI 15
CHECK IRREGULARITIES CODE IS1893 2016
ZONE 0.36 RF 5 I 1.2 SS 1 ST 5 DM 0.05
17 FX 4.4482 MY 1.11205
18 FX 4.4482 MY 1.11205
19 FX 4.4482 MY 1.11205
17 FX 4.4482 MY -1.11205
18 FX 4.4482 MY -1.11205
19 FX 4.4482 MY -1.11205
17 FZ 4.4482 MY 3.3183572
18 FZ 4.4482 MY 3.158222
19 FZ 4.4482 MY 3.2049281
17 FZ 4.4482 MY -1.11205
18 FZ 4.4482 MY -1.11205
19 FZ 4.4482 MY -1.11205
PERFORM ANALYSIS
PRINT ANALYSIS RESULTS
PRINT DIA CR
FINISH


 -IRREGULARITY CHECKS
STAAD.PRO IRREGULARITIES CHECK - (  IS1893-2016  )   v1.2
*********************************************************
Including Amendment no. 2 November 2020
*********************************************************
--TORSION IRREGULARITY CHECKS
Torsion Irregularity Check
Ref: Table 5 (i)    - Ratio Limit(s): Lower-1.20 Upper-1.40
---------------------------------------------------------------------
edi : Design Eccentricity
esi : Static Eccentricity
bi  : Floor/Diaphragm plan dimension perpendicular to force direction
For Details Refer Clause 7.8 IS1893:2016-Part-1
---------------------------------------------------------------------
Using edi = 1.5esi + 0.05bi
---------------------------
Displacement of extreme points of diaphragm(dia.) in X dir.
------------------------------------------------------------------------
Dia.  Node Max. Disp.  Node Min. Disp. Avg. Disp. Max./Avg.  Status
(mm)             (mm)      (mm)      Disp.
------------------------------------------------------------------------
1      7    0.4984      2    0.4662    0.4823    1.0333     PASS
2     12    2.4871      9    2.3990    2.4430    1.0180     PASS
3     16    6.1637     13    6.0157    6.0897    1.0122     PASS
Using edi = esi - 0.05bi
------------------------
Displacement of extreme points of diaphragm(dia.) in X dir.
------------------------------------------------------------------------
Dia.  Node Max. Disp.  Node Min. Disp. Avg. Disp. Max./Avg.  Status
(mm)             (mm)      (mm)      Disp.
------------------------------------------------------------------------
1      2    0.4984      7    0.4662    0.4823    1.0333     PASS
2      9    2.4871     12    2.3990    2.4430    1.0180     PASS
3     13    6.1637     16    6.0157    6.0897    1.0122     PASS
Using edi = 1.5esi + 0.05bi
---------------------------
Displacement of extreme points of diaphragm(dia.) in Z dir.
------------------------------------------------------------------------
Dia.  Node Max. Disp.  Node Min. Disp. Avg. Disp. Max./Avg.  Status
(mm)             (mm)      (mm)      Disp.
------------------------------------------------------------------------
1      3    0.2699      2    0.2383    0.2541    1.0622     PASS
2     10    1.0087      9    0.9347    0.9717    1.0381     PASS
3     14    2.0463     13    1.9160    1.9812    1.0329     PASS
Using edi = esi - 0.05bi
------------------------
Displacement of extreme points of diaphragm(dia.) in Z dir.
------------------------------------------------------------------------
Dia.  Node Max. Disp.  Node Min. Disp. Avg. Disp. Max./Avg.  Status
(mm)             (mm)      (mm)      Disp.
------------------------------------------------------------------------
1      3    0.3916      2    0.2319    0.3118    1.2562   WARNING*
2     10    1.3253      9    0.9131    1.1192    1.1841     PASS
3     14    2.5782     13    1.8732    2.2257    1.1584     PASS
*** WARNING: The floor is irregular.  Please ensure conformance
with Cl. 7.1, Table 5, Sl No. (i) sec-i.a or sec-i.b.
--GEOMETRY IRREGULARITY CHECKS
Re-Entrant Corner Check.
(Ref: Table 5 (ii)   - Ratio Limit: 0.15 )
------------------------------------------
***NOTE: No Irregular Re-Entrant Nodes found in the diaphragm.
***NOTE: No Irregular Re-Entrant Nodes found in the diaphragm.
***NOTE: No Irregular Re-Entrant Nodes found in the diaphragm.
--MASS IRREGULARITY CHECKS
Mass Irregularity Check
Ref: Table 6 (ii)   - Ratio Limit: 1.50
---------------------------------------
Dia.   Level     Mass       Above      Below     Ratio  Ratio  Status
( m)      ( kN)      ( kN)      ( kN)     Above  Below
---------------------------------------------------------------------
1     5.000    166.404    166.404    Base      1.000   N/A     OK
2    10.000    166.404    117.808    166.404   1.412  1.000    OK
3    15.000    117.808    Top        166.404    N/A   0.708    OK
***NOTE: Linear dynamic analysis needs to carried out for Irregular
Modes of Oscillation check.
***NOTE: Static Seismic Loads for relevant code needs to be defined
with Zone 4 and 5 for Irregular Modes of Oscillation  check.