Scale Factor -Responses Spectrum

As I refer to Application Examples U.k. No 11  Response spectrum analysis of a frame.

The response spectrum was define as below:

SPECTRUM CQC X 1.0 ACC DAMP 0.05 SCALE 9.806
0.03 1.00 ; 0.05 1.35
0.1 1.95 ; 0.2 2.80
0.5 2.80 ; 1.0 1.60

Notes: The UNIT applied is in METER KNS. The units for acceleration supposed to be in m/s2

However in the result page indicate  the  acceleration in the unit of G instead within the same decimal point as in the input values.

As 1 g=9.806m/s2, why the units in g are not divided by that value of 9.806 in the unit of G?

       MODE                 ACCELERATION-G     DAMPING
           ----                 --------------     -------
              1                      2.74136       0.05000
              2                      1.36735       0.05000

Wondering how the scale factor of 9.806 being applied within the analysis. In this case the total base shear would be 9.806 time more than the expected value.

Can anyone helps to explain this.

  • The Base Shear directly proportional to the spectral acceleration.

    Now the numbers 2.74136 and 1.36735 shown in the output file under the " ACCELERATION-G" are a fraction of “g”. The value of spectral acceleration thus obtained product of this fractional value and user defined SCALE FACTOR.

    So, if you define the SCALE FACTOR of 9.806, then it is only going to magnify the fraction by the scale factor.



  • Thank Geeky for the explanation .
    However I did observe that the acceleration 2.74136 g is actually from the interpolation under mode 1 period 0.19312 secs.
    My question actually over the units used here.
    From the input file , the unit of acceleration was in m/sec2
    Once the acceleration table reappear in the output table, the unit was changed into G which is different from the input unit in m/sec2.
    Just wondering does the scale factor 9.806 magnified the magnitude and is that value appropriate, or the scale supposed to be in 0.9806 as 1 G actually representing 9.806m/sec2.