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Seismic action

Loadcap NX reduces the bearing capacity in seismic conditions accounting for both the kinematic effect (on the soil) and the inertial effect (on the structure). The Seismic action card adapts to the chosen standard.

With NTC 2018: full hazard

With NTC 2018, the card shows the site seismic hazard:

  • Location (lat/lon WGS84), nominal life V_N and use class;
  • the table of the four limit states (SLO, SLD, SLV, SLC) with a_g, F_0, T_C*;
  • the subsoil category (A…E) and the topographic category (T1…T4), which determine the amplification coefficients S_S, C_C, S_T;
  • the elastic response spectrum, drawn in real time.

From these data Loadcap derives the seismic coefficients:

  • k_h (soil) and k_v = ±0.5·k_h;
  • k_hi (structure) = S_e(T₁) / q, with period T₁ = c₁·H^¾.

Import from GeoStru PS

The Import from GeoStru PS button reads the text file exported by the GeoStru seismic-hazard service and automatically fills location, categories and the four limit states.

Soil and structure: two distinct effects

Under seismic conditions two reductions of the bearing capacity come into play:

  • Kinematic effect (soil) — due to the acceleration passing through the foundation soil; it depends on k_h.
  • Inertial effect (structure) — due to the inertia forces transmitted by the superstructure; it depends on k_hi, related to the fundamental period T₁ and the behaviour factor q.

The Cascone-Maugeri method combines the two contributions into a correction factor on the N_γ term. The dedicated panel in the card explains the difference between the two coefficients and how they are computed.

Fundamental period T₁

T₁ is computed as c₁·H^¾ (c₁ = 0.085 steel · 0.075 r.c. · 0.050 other structures) or it can be assigned directly.

With Eurocode / other standards: direct coefficients

With Eurocode 8 or standards other than the NTC, the card shows the direct seismic coefficients: enter k_h, k_v, a_g and k_hi taken from the reference standard (no spectrum and no GeoStru PS import). Loadcap applies them to the bearing-capacity factors.

Effect on the calculation

When the seismic action is active, the bearing-capacity factors (particularly N_γ) reduce and, consequently, the ultimate load reduces. The geotechnical report includes the "Seismic hazard and actions" section with the limit-state table and the applied coefficients.

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