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V. ASCE 7 Mass Irregularity

Verify mass irregularity check in accordance to the ASCE 7-16 specifications.

Details

A three story structure is modelled with floor diaphragms defined at the story levels.

Isometric and Plan View of Structure

Seismic parameters:
  • Zip code = 92887
  • Importance factor, I = 1.0
  • Response reduction factor in X, Rx = 3
  • Response reduction factor in Z, Rz = 4
  • Site class A
  • Long period, TL = 8 sec

Verification

Diaphragm 1 = 1st Floor: Weight = 10 x 4 = 40 kN

Diaphragm 2 = 2nd Floor: Weight = 16 x 4 = 64 kN

Diaphragm 3 = 3rd Floor: Weight = 23 x 4 = 92 kN

Diaphragm Current Floor Weight

(KN)

Above Floor Weight

(KN)

Below Floor Weight

(KN)

Current Floor Weight/Above Floor Weight Current Floor Weight/Below Floor Weight Status (FAIL if ratio > 1.5)
1 40 64 N.A. 0.625 N.A. OK
2 64 92 40 0.696 1.6 FAIL
3 92 N.A. 64 N.A. 1.4375 OK

Results

Table 1. Comparison of results
Result Type Reference STAAD.Pro Difference Comments
Diaphragm 1 Ratio of 1st/2nd floor weights 0.625 0.625 none  
Check OK OK none  
Diaphragm 2 Ratio of 2nd/3rd floor weights 0.696 0.696 none  
Check OK OK none  
Ratio of 2nd/1st floor weights 1.6 1.6 none  
Check Fail Fail none  
Diaphragm 3 Ratio of 3rd/2nd floor weights 1.438 1.437 negligible  
Check 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 Mass Irregularity.STD is typically installed with the program.

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 03-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;
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
1 TO 24 PRIS YD 0.5 ZD 0.5
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
JOINT LOAD
2 3 6 7 FY -10
9 TO 12 FY -16
13 TO 16 FY -23
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 STATIC_X
IBC LOAD X 1
LOAD 2 LOADTYPE None  TITLE STATIC_Z
IBC LOAD Z 1
PERFORM ANALYSIS PRINT LOAD DATA
PRINT ANALYSIS RESULTS
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   0.24199      2   0.24199      3   0.24199      2   0.24199
    2     12   0.85035      9   0.85035     10   0.85035      9   0.85035
    3     16   1.62595     13   1.62595     14   1.62595     13   1.62595
             Diaphragm  D X-max/avg  D Z-max/avg Status
             --------------------------------------
                   1     1.0000   1.0000        OK    
                   2     1.0000   1.0000        OK    
                   3     1.0000   1.0000        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     40.000     64.000    Base      0.625   N/A     OK    
    2    10.000     64.000     92.000     40.000   0.696  1.600   FAIL   
    3    15.000     92.000    Top         64.000    N/A   1.437    OK