Response Spectrum Method for the Earthquake Check According to ÖNORM B 4015

The soil acceleration and the calculation coefficients as defined according to ÖNORM B 4015 based on the earthquake zone, the foundation, the damping and the ductility of the structure. For the check the reactions of the structure corresponding to the resonant frequencies are calculated according to the response spectrum method and superposed based on the SRSS or CQC method. The resulting internal forces are available for further superposition with the static load cases and subsequent design (for instance, according to ÖNORM B 4700).

To allow for the evaluation of the relevant modes of vibration, the program outputs the applied as well as the effective modal masses:

Sum of the applied masses (global)

                 Mx [t]       My [t]     Mz [t]
-----------------------------------------------
Dead weights:   1500.000     1500.000      0.000
Point masses:      0.000        0.000      0.000
-----------------------------------------------
Sum:         1500.000     1500.000      0.000

Effective modal masses (global)

Eigenmode    Mx eff [t]  My eff [t]  Mz eff [t]
------------------------------------------------
   1           935.135       0.000       0.000
   2             0.000     935.135       0.000
   3             0.000     287.137       0.000
   4           287.137       0.000       0.000
   5            98.544       0.168       0.000
   6             0.168     98.548       0.000
   7            47.342       3.197       0.000
   8             3.201      47.258       0.000
------------------------------------------------
Sum:         1371.526    1371.443       0.000

In this context, the ratio of the sums of the masses (effective modal masses/total mass) is of interest.

Example: 3D reinforced concrete frame

1st eigenmode	Corresponding internal forces My from the response spectrum
Superposed internal forces My according to CQC method