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ZERO SPECTRAL ACCELERATION ENTERED FOR MODE 1

 
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prash1730
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Joined: 02 Jul 2008
Posts: 2

PostPosted: Thu Aug 15, 2019 6:33 am    Post subject: ZERO SPECTRAL ACCELERATION ENTERED FOR MODE 1 Reply with quote

Dear All,
I am performing CQC method of response spectrum analysis and getting the warning as below.
   **WARNING- ZERO SPECTRAL ACCELERATION ENTERED FOR MODE   1
Request you to let me know the possible issues.
The structure is a space frame with roof truss is released for moments at ends as it is prestressed beam.
CQC response spectrum is defined as below.
The base shear values are NULL as indicated in the below extract.
Request your advise on how to go resolve the same as we are in the midst of a crucial deliverable.
LOAD 16 LOADTYPE Seismic  TITLE EQX - SEISMIC
REFERENCE LOAD
R1 1.0 R2 1.0 R3 1.0 R4 0.8 R5 0.8 R6 0.2
SPECTRUM CQC X 0 ACC DAMP 0.05 LIN
0 3.59281; 0.05 3.75612; 0.075 3.83778; 0.093 3.89657; 0.15 4.08274;
0.5 4.08274; 0.527 3.87357; 0.55 3.71159; 0.6 3.40229; 0.8 2.55171; 0.9 2.26819;
1 2.04137; 1.2 1.70114; 1.6 1.27586; 2 1.02069; 2.5 0.653239; 2.75 0.539867;
3 0.453638; 3.25 0.386532; 3.5 0.333285; 3.75 0.290328; 4 0.27468;
LOAD 17 LOADTYPE Seismic  TITLE EQY- SEISMIC
SPECTRUM CQC Y 0 ACC DAMP 0.05 LIN
0 2.31; 0.01 2.373; 0.025 2.467; 0.05 2.625; 0.05 2.625; 0.15 2.625;
0.25 1.575; 0.4 0.984; 0.5 0.787; 0.6 0.656; 0.75 0.525; 0.9 0.437; 1 0.394;
1.5 0.175;
LOAD 18 LOADTYPE Seismic  TITLE EQZ- SEISMIC
SPECTRUM CQC Z 0 ACC DAMP 0.05 LIN
***************Load combinations************************************
***************************SET-A************************************
0 3.59281; 0.05 3.75612; 0.075 3.83778; 0.093 3.89657; 0.15 4.08274;
0.5 4.08274; 0.527 3.87357; 0.55 3.71159; 0.6 3.40229; 0.8 2.55171; 0.9 2.26819;
1 2.04137; 1.2 1.70114; 1.6 1.27586; 2 1.02069; 2.5 0.653239; 2.75 0.539867;
3 0.453638; 3.25 0.386532; 3.5 0.333285; 3.75 0.290328; 4 0.27468;
========================================================================
==RESULTS==
           MODE                 ACCELERATION-G     DAMPING
           ----                 --------------     -------

              1                      0.00000       0.05000
   **WARNING- ZERO SPECTRAL ACCELERATION ENTERED FOR MODE   1
              2                      0.01099       0.05000
              3                      0.02077       0.05000
              4                      0.02926       0.05000
              5                      0.06170       0.05000
              6                      0.06530       0.05000



  MODAL BASE ACTIONS        FORCES IN KN   LENGTH IN METE
  -----------------------------------------------------------
                                                             MOMENTS ARE ABOUT THE ORIGIN
   MODE     PERIOD        FX          FY          FZ          MX          MY          MZ

      1      2.053        0.00        0.00        0.00        0.00        0.00        0.00
      2      1.653        0.00        0.00        0.00        0.00        0.00        0.00
      3      1.435        0.00        0.00        0.00        0.00        0.00        0.00
      4      1.244        0.00        0.00        0.00        0.00        0.00        0.00
      5      0.658        0.00        0.00        0.00        0.00        0.00        0.00
      6      0.618        0.00        0.00        0.00        0.00        0.00        0.00
    STAAD SPACE                                              -- PAGE NO.  196



           MASS  PARTICIPATION FACTORS IN PERCENT         BASE SHEAR IN KN
           --------------------------------------         ------------------

MODE    X     Y     Z     SUMM-X   SUMM-Y   SUMM-Z       X        Y        Z

   1    0.00  0.00 89.49    0.000    0.000   89.493      0.00     0.00     0.00
   2    3.70  0.00  0.01    3.705    0.000   89.503      0.00     0.00     0.00
   3   14.94  0.00  0.02   18.644    0.000   89.519      0.00     0.00     0.00
   4   75.29  0.00  0.00   93.937    0.000   89.520      0.00     0.00     0.00
   5    0.00  0.17  9.49   93.940    0.169   99.006      0.00     0.00     0.00
   6    4.22  0.00  0.00   98.164    0.170   99.006      0.00     0.00     0.00
                                                    ---------------------------
                                  TOTAL SRSS  SHEAR      0.00     0.00     0.00
                                  TOTAL 10PCT SHEAR      0.00     0.00     0.00
                                  TOTAL ABS   SHEAR      0.00     0.00     0.00
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rojanmathewtsy
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Joined: 21 Apr 2013
Posts: 29

PostPosted: Fri Aug 16, 2019 5:11 am    Post subject: Re: ZERO SPECTRAL ACCELERATION ENTERED FOR MODE 1 Reply with quote

prash1730 wrote:
Dear All,
I am performing CQC method of response spectrum analysis and getting the warning as below.
   **WARNING- ZERO SPECTRAL ACCELERATION ENTERED FOR MODE   1
Request you to let me know the possible issues.
The structure is a space frame with roof truss is released for moments at ends as it is prestressed beam.
CQC response spectrum is defined as below.
The base shear values are NULL as indicated in the below extract.
Request your advise on how to go resolve the same as we are in the midst of a crucial deliverable.
LOAD 16 LOADTYPE Seismic  TITLE EQX - SEISMIC
REFERENCE LOAD
R1 1.0 R2 1.0 R3 1.0 R4 0.8 R5 0.8 R6 0.2
SPECTRUM CQC X 0 ACC DAMP 0.05 LIN
0 3.59281; 0.05 3.75612; 0.075 3.83778; 0.093 3.89657; 0.15 4.08274;
0.5 4.08274; 0.527 3.87357; 0.55 3.71159; 0.6 3.40229; 0.8 2.55171; 0.9 2.26819;
1 2.04137; 1.2 1.70114; 1.6 1.27586; 2 1.02069; 2.5 0.653239; 2.75 0.539867;
3 0.453638; 3.25 0.386532; 3.5 0.333285; 3.75 0.290328; 4 0.27468;
LOAD 17 LOADTYPE Seismic  TITLE EQY- SEISMIC
SPECTRUM CQC Y 0 ACC DAMP 0.05 LIN
0 2.31; 0.01 2.373; 0.025 2.467; 0.05 2.625; 0.05 2.625; 0.15 2.625;
0.25 1.575; 0.4 0.984; 0.5 0.787; 0.6 0.656; 0.75 0.525; 0.9 0.437; 1 0.394;
1.5 0.175;
LOAD 18 LOADTYPE Seismic  TITLE EQZ- SEISMIC
SPECTRUM CQC Z 0 ACC DAMP 0.05 LIN
***************Load combinations************************************
***************************SET-A************************************
0 3.59281; 0.05 3.75612; 0.075 3.83778; 0.093 3.89657; 0.15 4.08274;
0.5 4.08274; 0.527 3.87357; 0.55 3.71159; 0.6 3.40229; 0.8 2.55171; 0.9 2.26819;
1 2.04137; 1.2 1.70114; 1.6 1.27586; 2 1.02069; 2.5 0.653239; 2.75 0.539867;
3 0.453638; 3.25 0.386532; 3.5 0.333285; 3.75 0.290328; 4 0.27468;
========================================================================
==RESULTS==
           MODE                 ACCELERATION-G     DAMPING
           ----                 --------------     -------

              1                      0.00000       0.05000
   **WARNING- ZERO SPECTRAL ACCELERATION ENTERED FOR MODE   1
              2                      0.01099       0.05000
              3                      0.02077       0.05000
              4                      0.02926       0.05000
              5                      0.06170       0.05000
              6                      0.06530       0.05000



  MODAL BASE ACTIONS        FORCES IN KN   LENGTH IN METE
  -----------------------------------------------------------
                                                             MOMENTS ARE ABOUT THE ORIGIN
   MODE     PERIOD        FX          FY          FZ          MX          MY          MZ

      1      2.053        0.00        0.00        0.00        0.00        0.00        0.00
      2      1.653        0.00        0.00        0.00        0.00        0.00        0.00
      3      1.435        0.00        0.00        0.00        0.00        0.00        0.00
      4      1.244        0.00        0.00        0.00        0.00        0.00        0.00
      5      0.658        0.00        0.00        0.00        0.00        0.00        0.00
      6      0.618        0.00        0.00        0.00        0.00        0.00        0.00
    STAAD SPACE                                              -- PAGE NO.  196



           MASS  PARTICIPATION FACTORS IN PERCENT         BASE SHEAR IN KN
           --------------------------------------         ------------------

MODE    X     Y     Z     SUMM-X   SUMM-Y   SUMM-Z       X        Y        Z

   1    0.00  0.00 89.49    0.000    0.000   89.493      0.00     0.00     0.00
   2    3.70  0.00  0.01    3.705    0.000   89.503      0.00     0.00     0.00
   3   14.94  0.00  0.02   18.644    0.000   89.519      0.00     0.00     0.00
   4   75.29  0.00  0.00   93.937    0.000   89.520      0.00     0.00     0.00
   5    0.00  0.17  9.49   93.940    0.169   99.006      0.00     0.00     0.00
   6    4.22  0.00  0.00   98.164    0.170   99.006      0.00     0.00     0.00
                                                    ---------------------------
                                  TOTAL SRSS  SHEAR      0.00     0.00     0.00
                                  TOTAL 10PCT SHEAR      0.00     0.00     0.00
                                  TOTAL ABS   SHEAR      0.00     0.00     0.00



From the command file above, what I can guess is that you have defined the Response Spectrum Wrongly.
I assume that you have defined the spectrum using custom option.
SPECTRUM CQC X 0 ACC DAMP 0.05 LIN, this line means that you have not entered any value for X direction component, so your defined spectrucm become null or zero value. You have to enter the value Z*I/(2*R) in that field based on the eq zone and other parameters as per code.

Rojan Mathew
mathew.rojan@gmail.com
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venkatasalamkl
SEFI Member
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Joined: 27 Oct 2017
Posts: 9

PostPosted: Fri Aug 16, 2019 4:30 pm    Post subject: ZERO SPECTRAL ACCELERATION ENTERED FOR MODE 1 Reply with quote

Hi,

Please check the time period of the structure (The issue might because of hight time period)


Also, Please have a look in bentley discussion. Link provided below:-


https://communities.bentley.com/communities/other_communities/chinafirst/w/chinawiki/25472/-warning--zero-spectral-acceleration-entered-for-mode-1




Thanks & Regards,
Venkat

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