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V.ASCE 7 Torsion Irregularity

Verify the torsional irregularity check per the ASCE 7-16 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.

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

Validation

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

Table 1. X direction checks
Diaphragm Master Node Primary LC Number Diaphragm Extremities Displacements (mm) Δmax/Δmin Status
Extreme Node 1 Extreme Node 2 Δx Extreme Node 1 Δx Extreme Node 2
1 17 1 2 or 3 6 or 7 0.0482 × 10 = 0.482 0.0482 × 10 = 0.482 0.482/0.482 = 1 OK
2 18 2 9 or 10 11 or 12 0.2443 × 10 = 2.443 0.2443 × 10 = 2.443 2.443/2.443 = 1 OK
3 19 3 13 or 14 15 or 16 0.6090 × 10 = 6.090 0.6090 × 10 = 6.090 6.090/6.090 = 1 OK
Table 2. Z direction checks
Diaphragm Master Node Primary LC Number Diaphragm Extremities Displacements (mm) Δmax/Δmin Status
Extreme Node 1 Extreme Node 2 Δz Extreme Node 1 Δz Extreme Node 2
1 17 4 2 or 6 3 or 7 0.0234 × 10 = 0.234 0.0361 × 10 = 0.361 0.361/0.234 = 1.543 FAIL
2 18 5 9 or 11 10 or 12 0.0919 × 10 = 0.919 0.1243 × 10 = 1.243 1.243/0.919 = 1.353 OK
3 19 6 13 or 15 14 or 16 0.1884 × 10 = 1.884 0.2441 × 10 = 2.441 2.441/1.884 = 1.296 OK

Results

Table 3. Comparison of results
Result Type Reference STAAD.Pro Difference Comments
X Direction 1 OK OK none  
2 OK OK none  
3 OK OK none  
Z Direction 1 Fail Fail none  
2 OK OK none  
3 OK OK none  

STAAD.Pro Input File

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\06 Loading\IBC\2018\ASCE7 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 
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
DEFINE REFERENCE LOADS
LOAD R1 LOADTYPE Mass  TITLE REF LOAD CASE 1
SELFWEIGHT X 1 
SELFWEIGHT Y 1 
SELFWEIGHT Z 1 
END DEFINE REFERENCE LOADS
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
CHECK IRREGULARITIES CODE ASCE7
DEFINE IBC 2018
ZIP 92887 I 1 RX 3 RZ 4 SCLASS 1 TL 8
LOAD 1 LOADTYPE None  TITLE Diaphragm 1 Unit Load FX
JOINT LOAD
17 FX 4.4482
LOAD 2 LOADTYPE None  TITLE Diaphragm 2 Unit Load FX
JOINT LOAD
18 FX 4.4482
LOAD 3 LOADTYPE None  TITLE Diaphragm 3 Unit Load FX
JOINT LOAD
19 FX 4.4482
LOAD 4 LOADTYPE None  TITLE Diaphragm 1 Unit Load FZ
JOINT LOAD
17 FZ 4.4482
LOAD 5 LOADTYPE None  TITLE Diaphragm 2 Unit Load FZ
JOINT LOAD
18 FZ 4.4482
LOAD 6 LOADTYPE None  TITLE Diaphragm 3 Unit Load FZ
JOINT LOAD
19 FZ 4.4482
PERFORM ANALYSIS
PRINT ANALYSIS RESULTS
PRINT DIA CR
FINISH

STAAD.Pro Output

 -IRREGULARITY CHECKS 
                    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      7   0.48231      2   0.48231      3   0.36107      2   0.23351
    2     12   2.44302      9   2.44302     10   1.24284      9   0.91874
    3     16   6.08970     13   6.08970     14   2.44124     13   1.88424
             Diaphragm  D X-max/avg  D Z-max/avg Status
             --------------------------------------
                   1     1.0000   1.2145       FAIL   
                   2     1.0000   1.1499        OK    
                   3     1.0000   1.1288        OK    
 --GEOMETRY IRREGULARITY CHECKS 
 Re-Entrant Corner Check.
 (Ref: Fig. C12.3-1 T2- 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: Fig. C12.3-2 T2- 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