prEN ISO 19901-2

SLOVENSKI STANDARD
01-januar-2025
Naftna in plinska industrija, vključno z nizkoogljično energijo - Posebne zahteve za
naftne ploščadi - 2. del: Postopki potresno varnega projektiranja in potresna
merila (ISO/DIS 19901-2:2024)
Oil and gas industries including lower carbon energy - Specific requirements for offshore
structures - Part 2: Seismic design procedures and criteria (ISO/DIS 19901-2:2024)
Erdöl- und Erdgasindustrie - Spezielle Anforderungen für Offshore-Anlagen - Teil 2:
Seismische Auslegungsverfahren und -kriterien (ISO/DIS 19901-2:2024)
Industries du pétrole et du gaz, y compris les énergies à faible teneur en carbone -
Exigences spécifiques relatives aux structures en mer - Partie 2: Procédures de
conception et critères sismiques (ISO/DIS 19901-2:2024)
Ta slovenski standard je istoveten z: prEN ISO 19901-2
ICS:
75.180.10 Oprema za raziskovanje, Exploratory, drilling and
vrtanje in odkopavanje extraction equipment
91.120.25 Zaščita pred potresi in Seismic and vibration
vibracijami protection
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 19901-2
ISO/TC 67/SC 7
Oil and gas industries including
Secretariat: BSI
lower carbon energy — Specific
Voting begins on:
requirements for offshore
2024-11-11
structures —
Voting terminates on:
2025-02-03
Part 2:
Seismic design procedures and
criteria
ICS: 75.180.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
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Reference number
ISO/DIS 19901-2:2024(en)
DRAFT
ISO/DIS 19901-2:2024(en)
International
Standard
ISO/DIS 19901-2
ISO/TC 67/SC 7
Oil and gas industries including
Secretariat: BSI
lower carbon energy — Specific
Voting begins on:
requirements for offshore
structures —
Voting terminates on:
Part 2:
Seismic design procedures and
criteria
ICS: 75.180.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2024
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
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Published in Switzerland Reference number
ISO/DIS 19901-2:2024(en)
ii
ISO/DIS 19901-2:2024(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions (Pending) . 1
4 Symbols and abbreviated terms (Pending) . 4
4.1 Symbols .4
4.2 Abbreviated terms .5
5 Seismic hazards . 6
6 Performance objectives, limit states and damage states . 6
6.1 General .6
6.2 Limit states and damage states .9
6.3 Performance objectives .10
6.4 Seismic risk category .10
6.5 DL limit state verification (using hazardous events with intensity = S ) .
aE, LE
6.6 NC limit state verification (using hazardous events with intensity = S ) .
aA, LE
6.7 Design procedure . 12
6.8 Methods for limit state verification .14
6.8.1 General .14
6.8.2 Limit state verification methods.14
7 Analysis types for structural response .16
7.1 Response spectrum analysis .16
7.2 Time history analysis .16
7.3 Nonlinear pushover analysis.18
8 Simplified procedure for determining S and S .
aE, LE aA, LE
8.1 General .18
8.2 Spectral accelerations .18
8.3 Site class .18
8.4 Site correction factor coefficients .19
8.5 1 000-year horizontal acceleration spectrum .21
8.6 1 000-year vertical acceleration spectrum . 22
8.7 Damping adjustment . 23
8.8 Determining S and S .
aE, LE aA, LE
9 Detailed procedure for determining S and S .
aE, LE aA, LE
9.1 Probabilistic seismic hazard analysis (PSHA).24
9.2 Deterministic seismic hazard analysis (DSHA) . 26
9.3 Dynamic site response analysis (DSRA).27
9.4 Determining C .
c
9.5 Determining S and S .
aE, LE aA, LE
10 Floating structures .30
10.1 C is either not well-defined or unknown . 30
r
iii
ISO/DIS 19901-2:2024(en)
10.2 effects of shock waves . 30
10.3 ELE (ULS check). 30
Annex A (informative) Additional information and guidance .31
Annex B (informative) Simplified action procedure spectral accelerations .42
Annex C (normative) Regional information .95
Bibliography .100

iv
ISO/DIS 19901-2:2024(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 67, Oil and gas industries including lower
carbon energy, Subcommittee SC 7, Offshore structures, in collaboration with the European Committee for
Standardization (CEN) Technical Committee CEN/TC 12, Oil and gas industries including lower carbon energy,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the second edition (ISO 19901-2:2022), which has been technically
revised.
The main changes are as follows:
— scope expanded to cover offshore wind and other renewable energy offshore structures;
— incorporates requirements from common industry specifications (IOGP JIP 35);
— the seismic hazard maps have been updated;
— written with clear and concise requirements.
A list of all parts in the ISO 19901 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
ISO/DIS 19901-2:2024(en)
Introduction
The International Standards on offshore structures prepared by TC 67 address design requirements and
assessments of all offshore structures used in the energy sector worldwide. Through their application, the
intention is to achieve reliability levels appropriate for normally occupied and normally unoccupied offshore
structures, whatever the type of structure and the nature or combination of the materials used.
Structural integrity is an overall concept comprising models for describing actions, structural analyses,
design or assessment rules, safety elements, workmanship, quality control procedures and national
requirements, all of which are mutually dependent. The modification of one aspect of design or assessment
in isolation can disturb the balance of reliability inherent in the overall concept or structural system. The
implications involved in modifications, therefore, need to be considered in relation to the overall reliability
of all offshore structural systems.
The International Standards on offshore structures prepared by TC 67 are intended to provide a wide
latitude in the choice of structural configurations, materials, and techniques without hindering innovation.
Sound engineering judgement is, therefore, necessary in the use of these International Standards.
The overall concept of structural integrity is described above. Some additional considerations apply for
seismic design. These include the magnitude and probability of seismic events, the use and importance of
the offshore structure, the robustness of the structure under consideration and the allowable damage due
to seismic actions with different probabilities. All of these, and any other relevant information, need to be
considered in relation to the overall reliability of the structure.
Seismic conditions vary widely around the world, and the design criteria depend primarily on observations
of historical seismic events together with consideration of seismotectonics and local soil conditions. In many
cases, site-specific seismic hazard assessments will be required to complete the design or assessment of a
structure.
This document is intended to provide general seismic design procedures for different types of offshore
structures, and a framework for the derivation of seismic design criteria. Further requirements are
contained within the general requirements International Standard, ISO 19900, and within the structure-
specific International Standards, ISO 19902, ISO 19903, ISO 19904, and ISO 19906. The consideration of
seismic events in connection with mobile offshore units is addressed in ISO 19905.

vi
DRAFT International Standard ISO/DIS 19901-2:2024(en)
Oil and gas industries including lower carbon energy —
Specific requirements for offshore structures —
Part 2:
Seismic design procedures and criteria
1 Scope
This document contains provisions for seismic design and assessment of offshore structures.
Recommendations for the effects of seismic events on floating structures are introduced.
Design and assessment of earthquake-induced ground motions are specifically addressed. Other geologically
induced hazards such as liquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves are
briefly covered.
Provisions for site-specific probabilistic seismic hazard analysis are provided for offshore structures in high
seismic areas and for offshore structures with high consequence levels.
NOTE Guidance and background information relating to the requirements is included in Annex A.
2 Normative references
The following documents are referred to in the text in such a way that some or all their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 19900, Oil and gas industries including lower carbon energy — General requirements for offshore structures
3 Terms and definitions (Pending)
For the purposes of this document, the terms and definitions given in ISO 19900 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
abnormal level earthquake
ALE
intense earthquake of abnormal severity with a very low probability of occurring during the life of the
structure, generally of return period in the 1 000’s of years.
Note 1 to entry: The ALE event is comparable to the abnormal event in the design of fixed structures that are described
[6] [7]
in ISO 19902 and ISO 19903 .
3.2
attenuation
decay of seismic waves as they travel from the earthquake source to the site under consideration.

ISO/DIS 19901-2:2024(en)
3.3
deaggregation
separation of seismic hazard contribution from different faults and seismic source zones
3.4
escape and evacuation system
system provided on the offshore structure to facilitate escape and evacuation in an emergency.
EXAMPLE Passageways, chutes, ladders, life rafts and helidecks.
3.5
extreme level earthquake
ELE
strong earthquake with a reasonable probability of occurring during the life of the structure, generally of
return period in the 100’s of years.
3.6
fault movement
movement occurring on a fault during an earthquake.
3.7
ground motion
accelerations, velocities or displacements of the ground produced by seismic waves radiating away from
earthquake sources.
Note 1 to entry: A fixed offshore structure is founded in or on the seabed (3.17) and consequently only seabed
motions are of significance. The expression "ground motions" is used rather than seabed motions for consistency of
terminology with seismic design for onshore structures.
Note 2 to entry: Ground motions can be at a specific depth or over a specific region within the seabed.
3.8
liquefaction
fluidity of soil due to the increase in pore pressures caused by earthquake action under undrained conditions.
3.9
modal combination
combination of response values associated with each dynamic mode of a structure.
3.10
mud volcano
diapiric intrusion of plastic clay causing high pressure gas-water seepages which carry mud, fragments of
rock (and occasionally oil) to the surface.
Note 1 to entry: The surface expression of a mud volcano is a cone of mud with continuous or intermittent gas escaping
through the mud.
3.11
probabilistic seismic hazard analysis
PSHA
framework permitting the identification, quantification, and rational combination of uncertainties in
earthquakes' intensity, location, rate of recurrence and variations in ground motion (3.7) characteristics.
3.12
probability of exceedance
probability that a variable (or that an event) exceeds a specified reference level given exposure time.
EXAMPLE The annual probability of exceedance of a specified magnitude of ground acceleration, ground velocity
or ground displacement.
ISO/DIS 19901-2:2024(en)
3.13
response spectrum
maximum responses of a series of single-degree-of freedom systems subjected to a given base motion,
plotted as a function of natural frequencies for specific values of damping.
3.14
safety system
systems provided on the offshore structure to detect, control and mitigate hazardous situations.
EXAMPLE Gas detection, emergency shutdown, fire protection, and their control systems.
3.15
sea floor
interface between the sea and the seabed (3.17)
3.16
seabed slide
failure of seabed (3.17) slopes
3.17
seabed
soil material below the sea in which a structure is founded.
3.18
seismic risk category
SRC
category defined from the consequence level and the intensity of seismic motions (i.e., the spectral
acceleration having an annual probability of exceedance of 1/1 000).
3.19
seismic hazard curve
curve showing the annual probability of exceedance (3.12) against a measure of seismic intensity.
Note 1 to entry: The seismic intensity measures can include parameters such as peak ground acceleration, spectral
acceleration (3.22), or spectral velocity (3.23).
3.20
seismic reserve capacity factor
factor indicating the structure’s ability to sustain ground motions due to earthquakes beyond the level of
the extreme level earthquake (3.5)
Note 1 to entry: Refer to A.9.3.6 for more detail.
3.21
site response analysis
wave propagation analysis permitting the evaluation of the effect of local geological and soil conditions on
the ground motions (3.7) as they propagate up from depth to the surface at the site.
3.22
spectral acceleration
maximum absolute acceleration response of a single degree of freedom oscillator subjected to ground
motions (3.7) due to an earthquake.
3.23
spectral velocity
maximum pseudo velocity response of a single degree of freedom oscillator subjected to ground motions
(3.7) due to an earthquake.
Note 1 to entry: The pseudo velocity spectrum is computed by factoring the displacement or acceleration spectra by
the oscillator’s circular frequency or the inverse of its frequency, respectively.

ISO/DIS 19901-2:2024(en)
3.24
spectral displacement
maximum relative displacement response of a single degree of freedom oscillator subjected to ground
motions (3.7) due to an earthquake.
3.25
static pushover analysis
application and incremental increase of a global static pattern of actions on a structure, including equivalent
dynamic inertial actions, until a global failure mechanism occurs.
3.26
tsunami
long period sea waves caused by rapid vertical movements of the sea floor (3.15)
Note 1 to entry: The vertical movement of the sea floor is often associated with fault rupture during earthquakes or
with seabed slides (3.16).
4 Symbols and abbreviated terms (Pending)
4.1 Symbols
a
tail slope of the seismic hazard curve
R
C site coefficient, a correction factor applied to the acceleration part (shorter periods) of a re-
a
sponse spectrum
C correction factor applied to the spectral acceleration to account for uncertainties not captured
c
in a seismic hazard curve
C seismic reserve capacity factor; see Formulae (7) and (10)
r
C site coefficient, a correction factor applied to the velocity part (longer periods) of a response
v
spectrum
D scaling factor for damping
G initial (small strain) shear modulus of the soil
max
g acceleration due to gravity
M magnitude of an earthquake measured by the energy released at its source
N scale factor for conversion of the site 1 000-year acceleration spectrum to the site ALE accel-
ALE
eration spectrum
p atmospheric pressure
a
P annual probability of exceedance for the ALE event
ALE
P probability of exceedance
e
P annual probability of exceedance for the ELE event
ELE
P target annual probability of failure
f
q cone penetration resistance of soil
c
q normalized cone penetration resistance of soil
cl
qc_""l
average normalized cone penetration resistance of sand in the effective seabed

ISO/DIS 19901-2:2024(en)
ST
() spectral acceleration associated with a single degree of freedom oscillator period, T
a
T
mean spectral acceleration associated with a single degree of freedom oscillator period, T;
obtained from a PSHA
is the spectral acceleration for a single degree of freedom oscillator periodT resulting from
ST
()
aA, LE
a suite of time histories that, when the structure is exposed to, would result in a probability
of collapse of 50 %.
ST
() ELE spectral acceleration associated with a single degree of freedom oscillator period, T
aE, LE
ST()
1 000-year rock outcrop spectral acceleration obtained from maps associated with a single
am, ap
degree of freedom oscillator period, T
ST
() mean spectral acceleration associated with a probability of exceedance, P , and a single de-
aP,
e
e
gree of freedom oscillator period, T, obtained from a PSHA
ST()
spectral acceleration having an annual probability of associated with a target annual proba-
aP,
NC
bility of failure, P , and a single degree of freedom oscillator period, T, obtained from a PSHA
f
ST
() site spectral acceleration corresponding to a return period of 1 000 years and a single degree
as, ite
of freedom oscillator period, T
s undrained shear strength of the soil
u
s̅ average undrained shear strength of the soil in the effective seabed
u
T natural period of a simple, single degree of freedom oscillator
T dominant modal period of the structure
dom
T return period
return
v representative shear wave velocity
s
average of representative shear wave velocity in the effective seabed
ρ mass density of soil
η per cent of critical damping
σ logarithmic standard deviation of uncertainties not captured in a seismic hazard curve
LR
σ′ in situ vertical effective stress of soil
v0
4.2 Abbreviated terms
DL damage limitation limit state
DSHA deterministic seismic hazard analysis
DSRA dynamic site response analysis
L1, L2, L3 consequence level derived in ISO 19900
MOU mobile offshore unit
NC near collapse limit state
NP nonlinear pushover
ISO/DIS 19901-2:2024(en)
NTHA nonlinear time history analysis
PGA peak ground acceleration
RP return period
THA time history analysis
TLP tension leg platform
ULS ultimate limit state
5 Seismic hazards
5.1 Seismic design and assessment of offshore structures shall include the effect of ground motions due to
earthquakes.
5.2 The design and assessment of offshore structures shall also include the effects of the following seismic
hazardous events, as developed by specialists in geologic site hazards:
a) soil liquefaction.
b) seabed slide.
c) fault movement.
d) tsunamis.
e) mud volcanoes.
f) velocity pulse from directivity effects.
6 Performance objectives, limit states and damage states
6.1 General
6.1.1 The risks, due to the structure being exposed to seismic hazardous events, shall be demonstrated to
be tolerable in conformance with 6.1.2 to 6.1.5.
NOTE 19901-2 requirements will result in the structure having sufficient strength and ductility such that the
risks (life-safety, environmental-pollution, and business-disruption) are tolerable when the structure is exposed to
seismic hazardous events as defined by the hazard curve for the site.
6.1.2 The structure shall meet the performance objectives (as defined in 6.3).
6.1.3 Demonstration that the structure meets the performance objectives shall be by limit state
verification in conformance with ISO 19900.
6.1.4 The performance objective for life-safety risk, typically associated with the ALE, shall specify the
maximum tolerable annual probability that the (damage) state of structure can exceed the Near Collapse
(NC) limit state.
NOTE 1 the NC limit state is described in 6.2.1. When the state of the structure is at the NC limit state, the structural
system remains stable, but one or more components can have failed. Since the structure remains stable and does not
collapse, fatalities are limited or avoided following the seismic event, and thus the life- life-safety consequence is
negligible
ISO/DIS 19901-2:2024(en)
6.1.5 The performance objective for business-disruption risk, typically associated with the ELE, shall
specify the maximum tolerable annual probability that the (damage) state of structure can exceed the
Damage Limitation (DL) limit state.
NOTE 1 the DL limit state is described in 6.2.2. When the state of the structure is at the DL limit state, the structural
system remains stable, but lateral system of the structure (braces, joints, and piles) can have strains approaching the
yield strain. Any damage is localised and readily repairable and thus the functionality of the facility is restored in a
short time scale following the seismic event, and thus the business-disruption consequence is tolerable.
Limit state verification for the DL and NC limit states shall be in conformance with clauses 6 to 10, as
illustrated in Figure 1.
ISO/DIS 19901-2:2024(en)
Figure 1 — Steps for limit state verification
NOTE limit state verification of SRC 3 facilities can be by clause 8 or clause 9

ISO/DIS 19901-2:2024(en)
6.2 Limit states and damage states
6.2.1 The state of the structure at the Near Collapse (NC) limit state associated with the ALE:
a) shall not include collapse of the structure’s gravity system (i.e. legs, soil axial capacity and pile to leg
connection) or collapse of the sub-system that supports the living quarters.
b) may include damage to members (e.g., plastic strains, plastic local buckling in steel or spalling in
concrete).
c) may include severed braces (by fracture or low-cycle fatigue).
d) may include plasticity at joints.
e) may include collapse or fracture of joints.
f) may include plastic tensile strain less than the fracture strain in piles.
NOTE DNV-RP-C208 provides guidance on fracture limits for local strain.
g) shall not include damage to safety systems, escape routes, and evacuation systems that prevent their
functionality.
h) shall not include loss of supports for critical hydrocarbon equipment that could lead to escalation by
loss of process containment (LOPC).
i) shall not include collapse of the living quarters, masts, derricks, flare structures and other safety
critical structures.
6.2.2 The state of the structure at the Damage Limitation (DL) limit state associated with the ELE:
a) shall not include damage to the gravity system components of the structure (i.e. legs, soil axial capacity
and pile to leg connection).
b) shall not include damage due to brittle mechanisms (e.g., flexural buckling, local buckling in steel or
spalling in concrete).
NOTE ISO 19902 requires the seismic action is increased by a factor ofC for code checks of leg members
r
when the structure is subjected to seismic actions of intensity S
aE, LE
c) should limit strains at the outer fibre of braces, joints, and piles (i.e. bending plus axial strain) to the
yield strain.
NOTE ISO 19902 requires the lateral system (braces, joints, and piles) are dimensioned for ductility and thus
can plastically strain without local buckling during seismic actions of intensity S
aA, LE
d) shall not include damage to safety systems, escape routes, and evacuation systems that prevent their
functionality.
e) shall not include damage to pipelines, conductors, risers, and other safety-critical components due to
displacements at mudline elevation of the structure.
f) shall not include damage due to toppling of topsides equipment and cable trays.
g) shall not include damage to masts, derricks, and flare structures.
h) shall not include damage to sliding supports that prevent their functionality.
i) shall not include damage to piping systems that prevents their functionality due to differential
displacement of supports.
j) should not include damage that will result in dropped objects.

ISO/DIS 19901-2:2024(en)
6.3 Performance objectives
6.3.1 The NC limit state verification of the structure shall be demonstrated for the ALE event in
conformance with 6.3.2.
6.3.2 The annual probability of the structure exceeding the NC limit state, as defined in 6.2.1, shall not be
greater than the value of P listed in Table 1.
NC
Table 1 — Maximum annual probability of exceeding NC limit state.
Consequence level P
NC
−4
L1 4 × 10 = 1/2 500
−3
L2 1 × 10 = 1/1 000
−3
L3 2,5 × 10 = 1/400
NOTE 1 The annual probability in Table 1 for the NC accounts for the epistemic uncertainty in the annual probability
and is determined by use of the mean hazard curve and the mean fragility curve.
NOTE 2 the simplified procedure in clause 8 has been calibrated to the probabilities listed in Table 1.
6.3.3 The maximum annual probability of exceeding the NC limit state may be less than listed in Table 1 if
specified by the operator or regulator.
6.3.4 The DL limit state verification of the structure shall be demonstrated in conformance with the ELE
events defined in 6.3.5.
6.3.5 The annual probability of the as-designed structure exceeding the DL limit state, as defined in 6.2.2,
shall not be greater than P or the value of P listed in Table 2.
ELE DL
Table 2 — Maximum annual probability of exceeding the DL limit state.
Consequence level
P
DL
L1 1/200
L2 1/100
15/ 0
L3
where Pis defined in Figure 7.
ELE
6.4 Seismic risk category
6.4.1 The facility shall be classed by seismic risk category (SRC) in conformance with Table 3.
NOTE SRC is a function of consequence level and site seismic zone.

ISO/DIS 19901-2:2024(en)
6.4.2 Site seismic zone shall be determined from the 1,0 s horizontal spectral acceleration maps in
Annex B or from a site specific seismic hazard study.
Table 3 — Seismic risk category (SRC)
Consequence level
S ()1,0
Site seismic
a ,map
(see ISO 19900: 2019, Cl 7.3)
zone
(see Annex B)
L1 L2 L3
<0,03 g 0 SRC 1 SRC 1 SRC 1
0,03 g to 0,10 g 1 SRC 3 SRC 2 SRC 2
0,11 g to 0,25 g 2 SRC 4 SRC 2 SRC 2
0,26 g to 0,45 g 3 SRC 4 SRC 3 SRC 2
>0,45 g 4 SRC 4 SRC 4 SRC 3
6.4.3 For seismic design situations, a structure shall not be classified as consequence level L2 unless
it is normally unoccupied (except for brief periods of time such as inspection and maintenance), but with
environmental-pollution consequence level greater than L3.
NOTE It is assumed that no reliable forewarning of seismic actions is feasible and, consequently, it is not possible
to evacuate prior to an earthquake.
6.5 DL limit state verification (using hazardous events with intensity = S )
aE, LE
6.5.1 S shall be determined in conformance with clause 8 or clause 9, depending on the SRC (as
aE, LE
described in 6.8).
6.5.2 DL limit state verification shall be performed using:
a) actions arising from ground motion time histories where each ground motion has a spectral acceleration,
at the sway period of the structure, defined by S .
aE, LE
b) representative capacities of members, joints, piles, and soil, as defined in ISO 19900.
NOTE clause 7 provides analysis types and requirements to determine the above actions.
6.5.3 DL limit state verification of the structure shall be deemed to have been demonstrated provided
ISO 19902:2020 formula 11.5-1 and 11.5-2 are satisfied.
6.6 NC limit state verification (using hazardous events with intensity = S )
aA, LE
6.5.1 S shall be determined in conformance with clause 8 or clause 9, depending on the SRC (as
aA, LE
described in 6.8).
6.6.1 NC limit state verification shall be performed using:
a) actions arising from ground motion time histories where each ground motion has a spectral acceleration,
at the sway period of the structure, defined by S .
aA, LE
b) mean capacities of members, joints, piles, and soil (by use of mean yield stress, mean component
capacities and expected soil capacity)
NOTE 1 representative capacities, R , as defined in ISO 19900, can be used to avoid determining the mean
k
capacities, however, this introduces conservatism into the NC limit state verification.
NOTE 2 clause 7 provides analysis types and requirements to determine the above actions.

ISO/DIS 19901-2:2024(en)
6.6.2 NC limit state verification of the structure shall be deemed to have been demonstrated provided
that no more than 3 of 7 ground motion records (each having a spectral acceleration at the sway period of
the structure defined by S ) cause collapse of the structure in a nonlinear time-history analysis.
aA, LE
6.7 Design procedure
6.7.1 The design procedure shall follow either:
a) the two-stage procedure described in 6.7.2
b) the three-stage procedure described in 6.7.3
NOTE the basis of the three-stage procedure is similar to that for the two-stage procedure, but the structure is
more likely to achieve the NC limit state verification without re-sizing members or joints.
6.7.2 Two-stage seismic design procedure
The two-stage design procedure consists of two steps as explained in the following and shown in Figure 2:
Figure 2 — Two-stage seismic design procedure
Stage 1. ELE Linear Design Checks
Perform linear ELE Response spectra analyses:
— DL limit state verification shall be satisfied for jacket braces and foundation pile stresses (mainly due to
bending).
Stage 2. ALE Nonlinear Verification
Perform verification nonlinear ALE analyses:
— Member checks – NC Limit state verification shall be satisfied for all the elements
— System checks – confirm the NC limit state is not reached before the ALE event
— Joint 100 % strength requirement – ensure braces fail before joints

ISO/DIS 19901-2:2024(en)
— Joint 100 % strength requirement may be relaxed when using an ALE nonlinear time history analysis or
nonlinear pushover analysis
NOTE nonlinear time history analysis or pushover analysis provide confidence in the joints meeting the NC limit
state. When performed correctly, nonlinear pushover analysis is a more rigorous check of joint strength than time-
history analysis.
6.7.3 Three-stage seismic design procedure
The three-stage design procedure consists of three steps as explained in the following and shown in Figure 3:
Figure 3 — Three-stage seismic design procedure
Stage 1. ELE Linear Design Checks
Perform linear ELE Response spectra analyses:
— DL limit state verification shall be satisfied for jacket braces and foundation pile stresses (mainly due to
bending).
— Designer may run linear ELE analyses using a lower C (see 9.5) for piles relative to the jacket structure.
r
NOTE using a linear ELE design check twice, once for jacket and the second for piles, with a lower Cr value for the
piles, limits failure away from the piles. This provides a check of the jacket separate from the foundation.
Stage 2. ALE Linear Design Checks
Perform linear ALE (ELE x Cr) response spectra analyses:
— DL limit state verification shall be satisfied for all the gravity-carrying members:
a. Legs;
b. Pile in compression;
c. Pile-soil axial resistance;
d. Joint cans
NOTE by ensuring linear performance of gravity-carrying members, nonlinearity for the ALE analysis is limited
to bending elements (e.g. bracing) which are ductile elements.

ISO/DIS 19901-2:2024(en)
Stage 3. ALE Nonlinear Verification
Perform verification nonlinear ALE analyses:
— Member checks – NC limit state verification shall be satisfied for all the elements
— System checks – confirm than NC limit state is not reached before the ALE event
— Joint 100 % strength requirement may be relaxed
...