Parameters of a structure seismic analysis depend on a seismic code used during calculations of a structure influenced by seismic impact. Select Indian seismic code (IS 1893) in the New Case Definition dialog or click Parameters in the Analysis Type dialog.
To complete the seismic analysis according to the rules given in this code, define the following parameters:
- Z - Seismic zone factor,
given in IS 1893 (Parts 1 to 5), clause 6.4.2 Table 3, the value is assigned according to the choice of seismic zone. For determining design seismic force, the country is classified into four seismic zones (II, II, IV, V) as shown in Figure 1.
- I - Seismic Importance Factor,
given in IS 1893 (Parts 1 to 5), clause 7.2.3 Table 8, the minimum value shall be:
- 1.5 for critical and lifeline structures,
- 1.2 for business continuity structures,
- 1.0 for the rest
- R - Response reduction factor,
given in IS 1893 (Parts 1 to 5) for the corresponding structures, clause 7.2.6 Table 9
- Site soil class
For determining the correct spectrum to be used, the type of soil on which the structure is placed shall be identified by the classification given in Table 4 clause 6.3.5.2, as:
- Soil type I - Rock or hard soil,
- Soil type II - Medium and stiff soil,
- Soil type III - Soft soil,
Spectrum for response analysis method
The design horizontal seismic acceleration coefficient Ahis based on the above factors, according to the formula 6.4.2 expression (b).
The design vertical seismic acceleration spectrum Av is determined accordingly by the formula 6.4.6 for building governed by IS 1893 (Part 1).
You can examine all the input parameters and base shear force distribution in the Calculation Notes (open Analysis > Calculation Notes > Simplified/Full Note)
In the lower part of the dialog, the the Direction definition and Filters buttons are located.
There is the additional button Design lateral force; click it to open the Base shear dialog. According to clause 7.7.3 base shear estimated by the Response Spectrum Method shall not be less than the design base shear calculated using a fundamental period Ta as per 7.6.2. You may choose different options to define fundamental period Ta or design base shear force value. Pay attention that internal forces, stresses and reaction will be scaled so that sum of reaction for quadratic combinations is equal to the design base shear.
The details concerning this structure analysis method can be found in the mentioned code of standard.
You can examine all the input parameters and spectrum values in the Calculation Notes (open Analysis > Calculation Notes > Simplified/Full Note).