Seismic (Pseudo-Static) Loading

Pseudo-static analysis represents earthquake shaking as constant body forces proportional to each slice's weight. You specify a horizontal coefficient and a vertical coefficient; the solver applies the corresponding forces to every slice and reports the resulting factor of safety.

Coefficients

Open Loading → Seismic Load and enter the coefficients. A single pair of coefficients applies to the whole model.

Click Apply Seismic Load to set the coefficients, or Clear Seismic Load to remove them (return both to 0).

Force application

For each slice of weight W:

• Horizontal force = k_h × W, applied in the failure direction.
• Vertical force = k_v × W, applied downward (a positive k_v adds to slice weight).

Sign convention

• The horizontal force acts in the direction of failure. For a left-to-right failure it points to the right; for a right-to-left failure it points to the left. A positive k_h is therefore destabilizing, driving the mass toward failure.
• A positive k_v increases the effective downward weight of each slice; a negative k_v reduces it. Enter a negative value to model upward vertical acceleration.

Guidance on coefficient values

The appropriate coefficients depend on site seismicity, the design code, and the acceptable deformation, and should be selected by the engineer. As rough guidance only:

• Horizontal coefficient k_h is commonly in the range 0 to about 0.4.
• Vertical coefficient k_v is commonly taken as roughly ±0.2, or zero when vertical acceleration is neglected.

These ranges are illustrative, not prescriptive. Use the values required by the governing standard for your project.

Note The coefficients are not clamped. Any finite value is accepted, so verify your inputs against the design code before running the analysis.