Earthquake Response Spectrum Module - Usage

The usage of the procedure can be summarised in several step:

Prepare a 3D model of building structural system, geometry and all vertical loading, and make certain it is running.

The model should have a minimum of 4 basic Load Cases, for instance:

1. G (dead load)
2. Q (live load)
3. Ex (earthquake force in X-X direction)
4. Ey (earthquake force in Y-Y direction)

The model must have a service Load Combination, which will be used to evaluate the mass of the structure used in the dynamic analysis.  For instance, we can define one load combination with 100% Deal Load and 40% Live Load.  In this case the load factors are: 1.0G + 0.4Q

On the Model and Solver Settings input panel select:
     Load Combination for Floor Mass Centroid: 1.0G + 0.4Q

Select:
     Load Case Earthquake in X-X: 3. Ex
     Load Case Earthquake in Y-Y:  4. Ey

Select the number of mode shapes.  Any number between 3 to 6 should be sufficient.  Then  select "Advanced 2D" option for evaluation of the model shapes.

Then, mesh and analyse the model.  Now, the stiffness matrix of the structural system is evaluated, and it is ready to be use in the frequency analysis.

Then, select [Solve > Frequency Analysis].  Now, a text report will open showing the frequency results.  The mode shapes and natural periods shown in the report will be used in the Spectral Analysis.

Then, go to [ Input > Lateral Load ], select basic "Load Case: 3. Ex", press on the "Earthquake AS 1170.4" button, select "Dynamic Analysis", select X-X direction and enter all input parameters and press OK. This will fill in the lateral load forces in the table for X-X direction. Select "Load Case: 4. Ey", and repeat the procedure.

Now, we have to perform 2nd Order Static Analysis, and examine the results.

The Earthquake load calculator allows usage of a general spectral curve.  In this case we only need to enter a Spectral Curve Factor.  Basically, R/C BUILDING sofgtware can use any Spectral Response Curve entered by the user, which is multiplied by a factor defined by the user.  If the Spectral Curve represent a real seismic event, some recorded earthquake the factor should be set to 1.0.

Note: Some basic knowledge of Structural Dynamics is necessary in order to use the Spectral module.

Spectral Curve Sample