Parameters of the seismic simplified analysis according to the equivalent lateral force method depend on a seismic code and a method of defining values of the fundamental periods selected in the Seismic Analysis dialog.
Approximate method
The fundamental period T1 is calculated according to the equation 4.6:
T1 = Ct * H3/4
where:
Ct - building period coefficient depending on the type of seismic-force-resisting system that is used (given by the code)
H - structure height (m) defined by difference between Structure range and Reference level
User-defined method
Only T1 - user defined fundamental period on both directions is to be defined.
Precise method
According to this method you can calculate the exact value for both X and Y directions. If the option Periods with maximal mass participation is off in the Seismic Analysis dialog, the first mode in direction where more masses is active. If this option is on, one of modes, which fulfill limitations and most masses, is active in the direction
Code parameters
To complete the seismic analysis according to the rules given in a code, define the following parameters.
- Value of ag - It specifies the design ground acceleration on type A ground as specified by Local Authorities. The design ground acceleration is defined in terms of the reference peak ground acceleration on type A ground agR and importance factor γ derived from the building class:
ag = γ × agR
- Value of the Behavior factor (q) according to point 3.2.2.5
- Value of the Beta factor lower bound factor for the horizontal design spectrum
- Ground type (A, B, C, D or E), as specified in the Table 3.1. It specifies parameters of the ground type influence that describe the response spectrum (S, Tb, Tc and Td) according to the tables 3.2, 3.3 and 3.4.
If the Envelope option is selected, the Parameters button becomes accessible; click it to open the Spectrum Envelope dialog.
- Spectrum type (type 1, type 2), as specified in point 3.2.2.
Base shear
Base shear force is calculated according to the formula:
Fb = Sd(T1) * m * λ (4.5)
Sd(T1) - value of design spectrum of response for period T1 according to the point 3.2.2.5
m - total mass of the building according to 3.2.4(2)
λ - correction factor, (0.85 or 1.0) set automatically basing on the Clause 4.3.3.2.2
Force distribution is performed according to the formula:
Fi = Fb * zi * mi / (Σ zj * mj) (4.11)
i=1.. storeysCount; j=1.. storeysCount
z - distance from reference level to mass position (appropriate floor)
m - mass according to 3.2.4(2)