Seismic action¶
SRS NX accounts for seismic action with a pseudostatic approach: a single horizontal seismic coefficient representing the increase in destabilising forces caused by an earthquake.
The K_h coefficient¶
In the Seismic parameters section set:
| Symbol | Parameter | Unit |
|---|---|---|
| I.11 K_h | Horizontal seismic coefficient | — |
With K_h = 0 (default) the check is purely static. With K_h > 0 SRS introduces two additional forces into the overburden wedge equilibrium:
- Horizontal seismic force
F_h = W · K_h - Vertical seismic force
F_v = F_h / 2
Both enter the computation of the resisting and acting shear forces (see Slope and substrate), reducing FS₀ and increasing the tension force required from the anchor.
Effect on the γ_Q1 coefficient¶
When K_h is non-zero, SRS applies the seismic-condition partial factor of actions γ_Q1 (γ_Q1 = 1.0 for both NTC 2018 and Eurocode) instead of the static one (γ_Q1 = 1.5). This coefficient multiplies the design tension and shear force on the anchor (E.10, E.11). See Design checks.
How to determine K_h¶
You can compute K_h with any code-based method of your choice, starting from the site's seismic hazard (ground acceleration a_g, subsoil and topographic category). Alternatively, SRS's AI assistant fetches the NTC seismic hazard parameters for a location and proposes a ready-to-review K_h value. See AI assistant.
Always check local amplification
The coefficient proposed by the assistant assumes unit stratigraphic and topographic amplification (S = S_S · S_T = 1). If the site's subsoil category or morphology implies significant amplification, increase K_h accordingly before using it in the design: the choice remains the designer's responsibility.
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