Pseudo-static seismic¶

Earthquake action on the wedge follows the NTC §3.2 / §7.11.3 pseudo-static formulation.

Parameters¶

Parameter	Symbol	Units	Notes
Horizontal seismic coefficient	α_s = k_h	–	NTC Tab. 7.11.I: kh = βs · amax / g (with βs reduction for natural slopes)
Seismic direction	Ω	°	rotation of the seismic vector with respect to horizontal; 0° = toward the valley

The vertical seismic coefficient k_v is not modelled as an independent parameter. The user can encode a vertical component by playing with Ω (≠ 0° pushes the force slightly upward or downward).

Equivalent force¶

The pseudo-static force applied at the wedge centroid is:

\[S = k_h \cdot W\]

with components:

\[S_x = -S \cdot \cos\Omega, \quad S_y = -S \cdot \sin\Omega\]

The minus signs follow the convention "seismic force away from the slope". The partial factor on seismic actions is γ_E = 1.0 (NTC §3.2.4).

Typical values¶

Site class / zone	NTC region	k_h typical
Class A (rock)	low seismicity	0.02–0.04
Class B/C	medium seismicity	0.05–0.10
Class A	high seismicity	0.08–0.12
Class C/D	high seismicity	0.12–0.20

On the section¶

The seismic force S is drawn as an arrow from the centroid G of the wedge, scaled to be visible (minimum 50 px). The label S = X kN/m is placed perpendicular to the arrow.

Common use¶

Set kh to the value required by the site classification, leave Ω = 0 (horizontal toward the valley). FS drops by roughly 1−0.5·k_h·tan α / tan(α − k_h) — typically 10–30% for moderate seismicity.