The parameters of the seismic simplified analysis according to the equivalent lateral force method depend on a seismic code and a method of defining the values of the fundamental periods selected in the Seismic Analysis dialog.
- Braced frames.
- Coupled walls.
- Other frames (other moment resisting frames).
- Other structures (other systems).
- RC frames (concrete moment resisting frames).
- Steel frames (steel moment resisting frames).
- Wall-frame systems.
- Walls.
Approximate method
The fundamental period (Ta) depends on the structure type, and on its effective height (hn). It is calculated according to point 4.1.8.11.3.
User-defined method
No restrictions are applied to user-defined values.
Precise method
When the Precise Method is used, the fundamental period (Ta) is expected to be following the results of Modal Analysis, but it will be verified against the limits provided in design code in point 4.1.8.11.3.(d). The limits of fundamental period (Ta) depend on the structure type and on the results obtained with the approximate formulas.
Code parameters
The code parameters for a seismic analysis according to NBC 2010 are defined as follows:
-
Site classifications for ground (A, B, C, D, E, F) conform with Table 4.1.8.4.A.
-
Factors (Sa(0.2), Sa(0.5), Sa(1.0), Sa(2.0), Fa and Fv) depend on the selected province, and conform with Table C-2.
The displayed factor values depend on the selected province and site. You can change these values manually or you can click Region to change the province and site of reference.
- Coefficients:
-
IE (Importance factor) conforms with table 4.1.8.5.
-
Rd (ductility-related force modification factor) and Ro (overstrength-related force modification factor) factors conform with Table 4.1.8.9.
-
In all cases, if the following condition (4.1.8.7.1.(a)) is not fulfilled, the lateral earthquake force will be equal to zero:
IEFaSa(0.2) < 0.35.
Base shear force (V)
Base shear force (V) is calculated according to the formula:
V = S(Ta) * Mv * Ie * W/(Rd * Ro)
- W is the seismic weight of the structure [N].
- Mv depends on Ta and ratio Sa(0.2)/Sa(2.0) and lateral resisting system type (according to table 4.1.8.11).
- S(Ta) is linearly interpolated between values calculated according to the formulas below:
- S(T)=Fa * Sa(0.2) for T <= 0.2 sec.
- S(T)=min(Fv * Sa(0.5), Fa * Sa(0.2)) for T = 0.5 sec.
- S(T)=Fv * Sa(1.0) for T = 1.0 sec.
- S(T)=Fv * Sa(2.0) for T = 2.0 sec.
- S(T)=Fv * Sa(2.0) for T >= 4.0 sec.
Fa and Fv are available in tables 4.1.8.4 B and C.
Disregard density
Excludes the density of the structure element (ρ=0) during the estimation of effective seismic weight applied to the stories of the structural model during analysis.