Seismic Analysis Parameters (EN 1998-1:2004)

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.

To complete the seismic analysis according to the rules given in a code, define the following parameters.

Fundamental period (T1)

Approximate method

The fundamental period T1 is calculated according to the equation 4.6:

T₁ = C_t * H^3/4

where:

C_t - 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.

a_g

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 a_gR and importance factor γ derived from the building class:

a_g = γ × a_gR

q

Specify the value of the Behavior factor (q) according to point 3.2.2.5.

Beta

Specify the value of the lower bound factor for the horizontal design spectrum.

Ground type

Select the type of ground (A, B, C, D or E), as specified in the Table 3.1.

The parameters of the ground type influence describe the response spectrum (S, Tb, Tc and Td) according to the tables 3.2, 3.3 and 3.4.

Note: Select Envelope to enable the Parameters button which allows you to open theSpectrum Envelope dialog.

Spectrum type

Select a Spectrum type as specified in point 3.2.2.

Base shear

Base shear force is calculated according to the formula:

F_b = S_d(T₁) * m * λ (4.5)

S_d(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:

F_i = F_b * z_i * m_i / (Σ z_j * m_j) (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)