Seismic Analysis Parameters (Canadian Code NBC 2010 - Static)

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.

The following structure types may be defined in each direction independently:

• 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 (T_a) depends on the structure type, and on its effective height (h_n). It is calculated according to the point 4.1.8.11.3. as follows:

T_a = C_t * (h_n) ^x

User-defined method

No restrictions apply on user-defined values.

Precise method

When the Precise Method is used, the fundamental period (T_a) depends on the structure type and on the results obtained with the Approximate Method. It is calculated according to the point 4.1.8.11.3.(d).

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) are conform to 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 are conform to Table C-2.

  The factor values displayed depend on the province and site selected. You can change these values manually, or click Region to change the province and site of reference.

• Coefficients:
  • IE (Importance factor) is conform to table 4.1.8.5.
  • Rd and Ro factors are conform to 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:

I_EF_aS_a(0.2) < 0.35.

Base shear force (V)

Base shear force (V) is calculated according to the formula:

V = S(T_a) * M_v * I_e * W/(R_d * R_o)

Where:

• W is the seismic weight of the structure [N].
• M_v depends on T_a and ratio S_a(0.2)/S_a(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)=F_a * S_a(0.2) for T <= 0.2 sec.
  • S(T)=min(F_v * S_a(0.5), F_a * S_a(0.2)) for T = 0.5 sec.
  • S(T)=F_v * S_a(1.0) for T = 1.0 sec.
  • S(T)=F_v * S_a(2.0) for T = 2.0 sec.
  • S(T)=F_v * S_a(2.0) for T >= 4.0 sec.

F_a and F_v are available in tables 4.1.8.4 B and C.