# TR.28.2.2 Check Irregularities

STAAD.Pro can check irregularities per the IS 1893 2016 and ASCE 7-05/10/16 seismic codes.

For IS 1893 2016, the program can check horizontal irregularities (torsional and reentrant corners) per Table 5 and vertical irregularities (mass irregularities and irregular modes of oscillation) per Table 6.

For ASCE 7-05/10/16, the program can check horizontal irregularities (torsional and reentrant corners) and vertical irregularies (mass). Irregular modes of oscillation are not considered for this code.

## Torsion Check per ASCE 7

Torsion checks per Cl. 12.3.2.1 of ASCE 7 2016 ( ref. fig C12.3-1 Type 1) are preformed by applying unit loads in each orthogonal direction to the control node of the diaphragm.

The unit load, F_{x}, is
applied at each diaphragm in the X-direction. After analysis, the program locates
the extreme nodes of the diaphragm and then d_{min} and d_{max} are
calculated. The ratio of d_{max}/d_{min} is evaluated and compared to the code
limit of 1.5. This process is then repeated in the Z direction for this diaphragm.
Then the similar process is applied to the other diaphragms in the structure.

## Torsion Check per IS 1893

Torsion checks per Table 5(i)-a IS 1893 2016 are performed by applying a unit force in each
orthogonal direction at two different distances (the design eccentricity,
e_{di}) as per Cl. 7.8.2. This results in
evaluating four different conditions for IS 1893 2016. The analysis is run and the
displacements of the two extreme ends of the diaphragm are extracted from the
analysis results. This ratio of these displacements is then reported with a status
based on the following limits:

Ratio | Status | Description |
---|---|---|

Δ_{max}/ Δ_{avg} <
1.2 |
OK | Indicates that the floor is regular and passes the irregularity checks. |

1.2 ≤Δ_{max}/ Δ_{avg}
≤1.4 |
Warning | Indicates that the floor is irregular and requires a full 3D
dynamic analysis in order to justify the structural configuration
or requires a change in structural configuration as per
Cl. 7.1, Table 5, Sl No. (i) sec-i.a and sec-i.b. |

Δ_{max}/ Δ_{avg} > 1.4 |
Fails | Indicates that the floor is irregular and fails the irregularity checks. The structural arrangement must be changed as per Cl. 7.1, Table 5, Sl No. (i) sec-ii. |

${e}_{\mathrm{di}}=\{\begin{array}{c}1.5{e}_{\mathrm{si}}+0.05{b}_{i}\\ {e}_{\mathrm{si}}-0.05{b}_{i}\end{array}$ | (Design eccentricity per IS 1893 2016 Cl. 7.8.2) |

_{si} | = | |

_{i} | = |

### Example floor diaphragm torsion for IS 1893

The unit load, F_{x} is applied at each diaphragm in the
X-direction in combination with two cases of M_{y} = F_{x}×
(e_{di} - e_{si}) representing the to cases for
e_{di}. After analysis, the program locates the
extreme nodes of the diaphragm and then Δ_{min},
Δ_{max}, and Δ_{avg}
values are calculated. The ratio of Δ_{max}/Δ_{avg}
is evaluated per the table above. This process is then repeated in the Z direction
for this diaphragm for a total of four cases at each diaphragm. Then the similar
process is applied to the other diaphragms in the structure.

## Reentrant Corners

The program will check for reentrant corners per Table 5(ii) of IS 1893 2016 and Cl. 12.3.2.1 of ASCE 7 2016 ( ref. fig C12.3-1 Type 2). The program first automatically identifies the boundary topology of the diaphragm. That is, the order in which analytical members and nodes of the boundary of the diaphragm are joined together to for a closed polygon. The program then determines the reentrant, or concave, corners of the diaphragm. The two analytical members joining the reentrant node is determined, their lengths are calculated, and then the projections of those lengths are calculated. To determine the ratios, the following are calculated:

L_{i}×cos(α)/L_{x} ≤ 0.15

L_{i}×cos(α)/L_{z} ≤ 0.15

If both members from the reentrant node are orthogonal, then for each
member, only 1 ratio is calculated as L_{i}/L_{x} for members oriented along the
x-direction and L_{i}/L_{z} for
members oriented along the z-direction.

### Example reentrant corner topology

All dependent nodes that form part of a diaphragm must lie within the same plane. Further, the boundary dependent nodes must form a closed polygon. Improper modeling of diaphragms may yield incorrect irregularity status results.

## Mass Irregularities

The program will check for mass irregularities per Table 6(ii) of IS 1893 2016 and Cl. 12.3.2.2 of ASCE 7 2016 (ref. fig C12.3-2 Type 2). The mass of each floor is calculated as the total of all floor diaphragm masses at the same level. The ratio of each floor mass to the floor above and below is calculated. These ratios are compared to the code stipulated values.

## Irregular Modes of Oscillation

Per Table 6(vii)-a, the sum of the percentage of mass participation for the first 3 lateral translational modes should contribute at least 65% in each principle plan direction. This is checked in both orthogonal directions.

Per Table 6(vii)-b, the time period for the fundamental modes in one direction should differ by at least 10%.

## IS 1893 2016 Example

An example using IS 1893 2016:

FLOOR DIAPHRAGM DIA 1 TYPE RIG HEI 3 DIA 2 TYPE RIG HEI 6 DIA 3 TYPE RIG HEI 9 CHECK IRREGULARITIES CODE IS1893 2016

## ASCE 7 Example

An example using ASCE 7:

FLOOR DIAPHRAGM DIA 1 TYPE RIG HEI 0 DIA 2 TYPE RIG HEI 5 CHECK IRREGULARITIES CODE ASCE7

## IS 1893 2016 Example Output

An example output section of an IS 1893 2016 seismic irregularities check:

-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.

## ASCE 7 Example Output

An example output section of an ASCE 7-2016 seismic irregularities check:

STAAD.PRO IRREGULARITIES CHECK - ( ASCE7-2016 ) v1.0 ***************************************************** --TORSION IRREGULARITY CHECKS Torsion Irregularity Check Ref: Fig. C12.3-1 T1- Ratio Limit(s): 1.20, 1.40 ------------------------------------------------ Dia. Extreme Points of Dia in X Extreme Points of Dia in Z Node Disp. Node Disp. Node Disp. Node Disp. (mm) (mm) (mm) (mm) ------------------------------------------------------------------------ 1 3 0.09130 1 0.09993 4 0.09484 1 0.10559 2 15 0.29636 13 0.30993 16 0.29819 13 0.34410 Diaphragm ΔX-max/avg ΔZ-max/avg Status -------------------------------------- 1 1.0451 1.0537 OK 2 1.0224 1.0715 OK --GEOMETRY IRREGULARITY CHECKS Re-Entrant Corner Check. (Ref: Fig. C12.3-1 T2- Ratio Limit: 0.15 ) ------------------------------------------ Node Re-Entrant X-Proj X-Proj/Lx Z-Proj Z-Proj/Lz Status Connectivity Node ( m) ( m) ---------------------------------------------------------------------- 6-> 5 0.0000 0.0000 7.0000 0.7778 Re-Entrant 4 1.0000 0.2000 0.0000 0.0000 18-> 17 0.0000 0.0000 7.0000 0.7778 Re-Entrant 16 1.0000 0.2000 0.0000 0.0000 Diaphragm: Lx: Lz: ( m) ( m) ---------------------------- 1 5.0000 9.0000 2 5.0000 9.0000 --MASS IRREGULARITY CHECKS Mass Irregularity Check Ref: Fig. C12.3-2 T2- Ratio Limit: 1.50 --------------------------------------- Dia. Level Mass Above Below Ratio Ratio Status ( m) ( kN) ( kN) ( kN) Above Below --------------------------------------------------------------------- 1 0.000 341.643 253.287 Base 1.349 N/A OK 2 5.000 253.287 Top 341.643 N/A 0.741 OK