Seism zones in Switzerland (SIA)

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SIA Seismic zones and loads map in Switzerland

Seismic zone map in Switzerland

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In Switzerland, seismic regions vary from seismic zone Z1a (lowest) to seismic zone Z3b (highest).

These zones indicate the variation of the maximal peak ground acceleration on type A ground in m/s².

Reference peak ground acceleration on type A ground in m/s², by zone according to SN 261:2020 §16.1 (+ Annex F)
Seism zones in Switzerland Z1a Z1b Z2 Z3a Z3b
Reference peak ground acceleration agd on type A ground in m/s² 0,6 0,8 1,0 1,3 1,6

Values of the periods and soil factor describing the shape of the horizontal response spectra
Ground type Parameters
A 1,00 0,07 0,25 2,00
B 1,20 0,08 0,35 2,00
C 1,45 0,10 0,40 2,00
D 1,70 0,10 0,50 2,00
E 1,70 0,09 0,25 2,00
F --- --- --- --- extract for a seism zone Z2


Seism standard
The standard SIA 261:2020 §16 (08/2020) and its annex Annexe F (08/2020) define the design rules and design methods for seismic actions on buildings.
Legislative texts about seism
  • Zoning: SN 261:2020 §, Seismic zones - Annex F of 01/08/2020
    • The construction is located at Davos Platz in a Moderate seismicity zone (zone Z2).
  • Zoning Map: Switzerland sismic zoning
  • Classification SN 261:2020 §16.3, Classes of works and factors of importance of 01/08/2020
  • Reference peak ground acceleration
    The intensity of the acceleration agd is function of the seismic zone. Its value of 1 m/s² is specified in SN 261:2020 §, Horizontal ground acceleration of 01/08/2020 .
    Use for importance classification:
    The building's use is of type "health and social establishment" or equivalent.
    According to SN 261:2020 §16.3, Classes of works and factors of importance of 01/08/2020 , the importance category associated to seism is III
    Importance factor of the building
    The factor γf is function of the importance category of the building. Its value of 1.5 is specified in SN 261:2020 §16.3, Classes of works, Table 25 of 01/08/2020 .
    Ground type
    The ground of construction is of type "C" :
    Deposits of moderately compact to compact sand and gravel or firm clay, a few dozen to several hundred metres thick.
    Horizontal design acceleration for a ground of type "C"
    The ground acceleration intensity is calculated as follows:

    Paraseismic checking
    A building belonging to the important class II requires the application of the standard SIA 261. § 25)
      Mandatory application of the rules SIA 261 for structural safety verification
      Mandatory application of SIA 261 rules for verification of aptitude for service
    Horizontal sizing spectrum for elastic analysis
    the design spectrum is determined from the elastic response spectrum for 5% viscous damping.
    It provides the maximum acceleration of the structure anchored to the ground during an earthquake. With, according to SIA261 §16.2.2(Tab. 24) :
    • the parameters of the design spectrum, function of the ground type and the seismicity zone:
      • T is the vibration period of a linear single-degree-of-freedom system.
      • the lower limit of the period of the constant spectral acceleration branch : TB = 0.1 s.
      • the upper limit of the period of the constant spectral acceleration branch : TC =0.4 s.
      • the value defining the beginning of the constant displacement response range of the spectrum : TD =2 s.
      • the design ground acceleration, taking into account the lithologic effects of site that amplify the seismic movement depending on the nature of the basement : agS = 2.17 m/s2.
    • behavior factor to take into account the energy dissipation capacity of the structure : q = 1.5 .
    • Sd(T) the horizontal design spectrum defined by the following expressions :
      • 0 ≤ T ≤ TB : (SIA261 : § (31))
      • TB ≤ T ≤ TC : (SIA261 : § (32))
      • TC ≤ T ≤ TD : (SIA261 : § (33))
      • TD ≤ T : (SIA261 : § (34))
    horizontal design spectrum
    Design ground displacement
    The design ground displacement is evaluated to
    (SIA261 : § (35))

    Vertical design acceleration
    The intensity of the design acceleration of the ground in the vertical direction is calculated as :
    (SIA261 : §, 01/08/2020)

    Design and construction measures

    Constructive measures for buildings are listed in SN 261:2020 §16.4. Their mandatory nature depends on the combination of earthquake zone (Z2) and structure class (III). Other measures may be prescribed in SIA 262 to 267.

    • Plan view, constructional arrangements:
    • These constructive measures are Exceptions to be justified (SN 261:2020 §16.4.1 Tab. 27)
      • In the plan, distribute the elements used to take up horizontal forces (frames, etc.) as symmetrically as possible. to absorb horizontal forces (frames, (frames, load-bearing walls with cores, triangular bracing, etc.) should be and provide for similar deformation capacities. Ensure behaviour of the structure through appropriate arrangement of of floors, bracing, etc.
      • For elements that have to take up horizontal forces, avoid variations (in the vertical direction) in the stiffnesses and resistance to bending, shear and torsion (exception: transition to basements).
      • Create a rigid casing in the basement area.
    • Building:
    • These constructive measures are Mandatory (SN 261:2020 §16.4.1 Tab. 27)
      • Connect the prefabricated elements to the other elements of the construction
      • For prefabricated elements with movable supports, provide a support length equal to 1/70 of the span, but at least 150 mm.
    • Foundation:
    • These constructive measures are Mandatory (SN 261:2020 §16.4.1 Tab. 27)
      • Do not design a load-bearing structure that rests on soils of very different stiffness.
      • To ensure uniform movement, avoid isolated foundations in soft ground or tie them together with sleepers.
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