ISO/FDIS 19901-2

FINAL DRAFT
International
Standard
ISO/TC 67/SC 7
Oil and gas industries including
Secretariat: BSI
lower carbon energy — Specific
Voting begins on:
requirements for offshore
2026-03-04
structures —
Voting terminates on:
2026-04-29
Part 2:
Seismic design procedures and
criteria
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
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
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ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
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
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
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
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INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 4
4.1 Symbols .4
4.2 Abbreviated terms .5
5 Seismic hazards . 6
6 Performance objectives and limit states. 6
6.1 General .6
6.2 Ultimate limit states .7
6.3 Performance objectives .8
6.4 Seismic risk category .9
6.5 ULS verification (using hazardous events with intensity = S ) .10
DL a,ELE
6.6 ULS verification (using hazardous events with intensity = S ) .10
NC a,ALE
6.7 Seismic design procedure .10
6.8 Methods for limit state verification .10
7 Analysis types for structural response .12
7.1 Response spectrum analysis . 12
7.2 Time history analysis . 13
7.3 Nonlinear pushover analysis.14
8 Simplified procedure for determining S and S . 14
a,ELE a,ALE
8.1 General .14
8.2 Spectral accelerations .14
8.3 Site class . 15
8.4 Site correction factor coefficients .16
8.5 1 000-year horizontal acceleration spectrum .17
8.6 1 000-year vertical acceleration spectrum .18
8.7 Damping adjustment .19
8.8 Determining S and S .19
a,ELE a,ALE
9 Detailed procedure for determining S and S .20
a,ELE a,ALE
9.1 Probabilistic seismic hazard analysis . 20
9.2 Deterministic seismic hazard analysis . 22
9.3 Determining C .
c
9.4 Determining S and S . 26
a,ELE a,ALE
9.5 Dynamic site response analysis .27
10 Floating structures .27
Annex A (informative) Additional information and guidance .28
Annex B (normative) Seismic maps with spectral accelerations for simplified action procedure . 41
Annex C (normative) Regional information .88
Bibliography .93

iii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 third edition (ISO 19901-2:2022), which has been technically
revised.
The main changes are as follows:
— the scope has been expanded to cover offshore wind and other renewable energy offshore structures;
— requirements from common industry specifications (IOGP JIP 35) have been incorporated;
— the seismic hazard maps have been updated.
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.

iv
Introduction
The International Standards for offshore structures prepared by ISO TC 67/SC 7 comprise:
— ISO 19900, the unifying International Standard for offshore structures;
— the ISO 19901 series, providing specific requirements for offshore structures;
— ISO 19902, ISO 19903, ISO 19904-1, the ISO 19905 series and ISO 19906, “structure type” standards.
Figure 1 illustrates the relationships between the International Standards for offshore structures prepared
by ISO TC 67/SC 7.
Figure 1 — Relationship of International Standards for offshore structures prepared by
ISO/TC 67/SC 7
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. Additional
information and guidance are given in Annex A, where the clause numbering mirrors the normative clauses
to facilitate cross referencing.

v
FINAL DRAFT International Standard ISO/FDIS 19901-2:2026(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 requirements for seismic design and assessment of offshore structures.
This document includes recommendations for the effects of seismic events on floating structures.
This document addresses specifically the design and assessment of offshore structures subjected to
earthquake-induced ground motions. It also covers briefly other geologically induced hazards such as
liquefaction, slope instability, fault surface displacement, tsunamis, mud volcanoes and shock waves.
This document provides requirements for site-specific probabilistic seismic hazard analysis for offshore
structures in high seismic areas and for offshore structures with high consequence levels.
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
ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
IOGP S-631-11, Supplementary Specification for Fixed Steel Offshore Structures, International Oil & Gas
Producers Association, Version 2, 8 February 2021
3 Terms and definitions
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
ground motion (3.6) due to a rare intense earthquake with a very low probability of occurrence during the
life of the structure
Note 1 to entry: Typically, having an annual probability of exceedance (3.10) of one in a few thousand years.
3.2
active fault
fault likely to have another earthquake in the future

3.3
attenuation
decay of seismic waves as they travel from the earthquake source to the site under consideration
3.4
deaggregation
separation of seismic hazard contributions from different faults and seismic source zones
3.5
extreme level earthquake
ELE
ground motion (3.6) due to an earthquake with a reasonable probability of occurring during the life of the
structure
Note 1 to entry: Typically having an annual probability of exceedance (3.10) of one in a few hundred years.
3.6
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 and consequently only seabed motions or
motions along the length of piles 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.
3.7
liquefaction
fluidity of soil due to the increase in pore pressures caused by earthquake action under undrained conditions
3.8
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.
3.9
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 (3.6) characteristics
3.10
probability of exceedance
P
e
probability that a variable (or an event) exceeds a specified reference level within a given exposure period
EXAMPLE The annual probability of exceedance of a specified magnitude of ground acceleration, ground velocity
or ground displacement.
3.11
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
3.12
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

3.13
safety system
system provided on the offshore structure to detect, control and mitigate hazardous situations
EXAMPLE Gas detection, emergency shutdown, fire protection, and their control systems.
3.14
seabed slide
failure of seabed slopes
Note 1 to entry: The seabed is defined as the soil material below the sea floor (ISO 19900:2019, 3.47).
Note 2 to entry: The effective seabed is defined in 8.3.2; typically, being the upper 30 m of seabed material.
3.15
seismic hazard curve
curve showing the annual probability of exceedance (3.10) against a measure of ground motion (3.6) or
response of the single degree of freedom oscillator
Note 1 to entry: The seismic measures can include parameters such as peak ground acceleration, spectral acceleration
(3.19), spectral velocity or spectral displacement.
3.16
seismic reserve capacity factor
C
r
factor indicating the structure’s ability to sustain ground motions (3.6) due to earthquakes beyond the level
of the extreme level earthquake (3.5)
3.17
seismic risk category
SRC
category defined from the consequence level and the intensity of seismic motions
3.18
site response analysis
wave propagation analysis permitting the evaluation of the effect of local geological and soil conditions on
the ground motions (3.6) as they propagate up from depth to the surface at the site
3.19
spectral acceleration
maximum acceleration response of a single degree of freedom oscillator subjected to ground motions (3.6)
due to an earthquake
3.20
tsunami
long period sea waves caused by rapid vertical movements of the sea floor
Note 1 to entry: The vertical movement of the sea floor is often associated with fault rupture during earthquakes or
with seabed slides (3.14).
3.21
zero pad
technique used in signal processing particularly when analysing earthquake recordings using the fast
Fourier transformation
4 Symbols and abbreviated terms
4.1 Symbols
a tail slope of the seismic hazard curve
R
C correction factor for the acceleration part (shorter periods) of a response spectrum
a
C correction factor applied to the spectral acceleration to account for uncertainties not
c
captured in a seismic hazard curve
C seismic reserve capacity factor
r
C correction factor for the velocity part (longer periods) of a response spectrum
v
d thickness of soil layer
D scaling factor for damping
G initial (small strain) shear modulus of the soil
max
g acceleration due to gravity
H horizontal spectral accelerations
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
ALE
acceleration spectrum
p atmospheric pressure
a
P annual probability of exceedance for the ALE event
ALE
P annual probability of exceedance for the ELE event
ELE
P annual probability of exceedance
e
annual probability of exceeding the ULS
P
DL
ULS
DL
P annual probability of exceeding the ULS
NC
ULS
NC
q cone penetration resistance of soil
c
normalized cone penetration resistance of soil
q
cl
average normalized cone penetration resistance of sand in the effective seabed
q
cl
R representative capacity
k
S (T) spectral acceleration (associated with single degree of freedom oscillator period, T)
a
S (T) ALE spectral acceleration
a,ALE
S (T ) ALE spectral acceleration at T
a,ALE dom dom
S (T) ELE spectral acceleration
a,ELE
S (T ) ELE spectral acceleration at T
a,ELE dom dom
S (T) 1 000-year bedrock spectral acceleration obtained from seismic maps
a,map
S (T) site spectral acceleration corresponding to a return period of 1 000 years
a,site
spectral acceleration having an annual probability of exceedance (P ) obtained from a
ST

e
a,P
e
PSHA.
ST site-specific spectral acceleration at T having an annual probability P of

dom
ad,P om ULS
ULS DL
DL
exceeding the ULS
DL
ST site-specific spectral acceleration at T having an annual probability P of

dom
ad,P om ULS
ULS NC
NC
exceeding the ULS
NC
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 vertical spectral accelerations
representative shear wave velocity
v
s
v
average representative shear wave velocity in the effective seabed
s
ρ mass density of soil
η per cent of critical damping
σ logarithmic standard deviation of uncertainties not captured in a seismic hazard
LR
curve
σ′ in situ vertical effective stress of soil
v0
4.2 Abbreviated terms
DL damage limitation state (specified in 6.2.3 and 6.2.4)
DSHA deterministic seismic hazard analysis
DSRA dynamic site response analysis
L1, L2, L3 consequence levels (see ISO 19900)
NC near collapse state (specified in 6.2.1 and 6.2.2)
NPA nonlinear pushover analysis
NTHA nonlinear time history analysis
RSA response spectrum analysis
SDOFS single degree of freedom
SLS serviceability limit state
SPA static pushover analysis
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 In addition to the effect of ground motion, 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 surface displacement,
d) tsunamis,
e) mud volcanoes,
f) velocity pulse from directivity effects (earthquake-induced shock wave in the water column typically
associated with volcanic eruptions).
NOTE Provisions for seismic design and assessment of floating structures is covered in Clause 10.
6 Performance objectives and limit 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 by stake holders in accordance with 6.1.2 to 6.1.5.
NOTE The requirements in this document ensure that the structure has 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 seismic hazard curve for the site.
6.1.2 Demonstration that the structure meets the performance objectives shall be by limit state
verification in accordance with ISO 19900.
6.1.3 The performance objective for life-safety and environmental risks, typically associated with an ALE,
shall specify the maximum tolerable annual probability that the (damaged) state of structure can exceed
ULS .
NC
NOTE 1 Life-safety risk refers to the potential for injury or loss of life during an earthquake.
NOTE 2 ULS is described in 6.2.1. When the state of the structure exceeds ULS one or more components can
NC NC
have failed and the structure can be near to collapsing.
6.1.4 The performance objective for business-disruption risk, typically associated with an ELE, shall
specify the maximum tolerable annual probability that the (damaged) state of structure can exceed ULS .
DL
NOTE ULS is described in 6.2.2. When the state of the structure exceeds ULS , the structural system remains
DL DL
stable, but the lateral system of the structure (braces, joints, and piles) can have plastic strains that result in permanent
deformation that can affect the functionality of the structure. The permanent deformation is likely repairable and
thus the functionality of the facility can be restored.

a
SRC 2 structures can alternatively be designed using the detailed seismic action procedure similar to SRC 3
and SRC 4 structures (see Table 4).
Figure 2 — Steps for limit state verification
6.2 Ultimate limit states
6.2.1 The state of the structure at the ULS , typically due to hazardous events with intensity S (T),
NC a,ALE
shall not include:
a) collapse of the structure’s gravity load resisting system (i.e. legs, pile to leg joints, pile-soil resistance) or
collapse of the gravity sub-system that supports the living quarters;
b) damage to safety systems, escape routes, and evacuation systems that prevent their functionality;

c) loss of supports for critical hydrocarbon equipment that could lead to escalation by loss of process
containment;
d) collapse of the living quarters, masts, derricks, flare structures and other safety critical structures.
6.2.2 The state of the structure at the ULS may include damage to the structure’s lateral system (i.e.
NC
braces and their joints, and pile lateral deformation) as follows:
a) severed braces (by fracture or low-cycle fatigue, with or without strain ratcheting);
b) plastic local buckling of braces or global buckling of braces;
c) permanent deformation of joints, and collapse or fracture of joints;
d) permanent lateral deformation of piles;
e) spalling of reinforced concrete.
6.2.3 The state of the structure at the ULS , typically due to hazardous events with intensity S , shall
DL a,ELE
not include:
a) permanent deformation of the components comprising the structure’s gravity load resisting system (i.e.
legs, pile to leg joints, and pile-soil resistance);
b) permanent deformation to the components comprising the structure’s lateral system (i.e. braces and
their joints, and pile lateral deformation);
c) damage to safety systems, escape routes, and evacuation systems that prevent their functionality;
d) damage to pipelines, conductors, risers, and other safety-critical components due to displacements at
mudline elevation of the structure;
e) damage due to toppling of topsides equipment and cable trays;
f) damage to masts, derricks, and flare structures;
g) damage to sliding supports that prevent their functionality;
h) damage to piping systems that prevents their functionality due to differential displacement of supports.
6.2.4 The state of the structure at the ULS should not include damage that will result in dropped objects.
DL
6.3 Performance objectives
6.3.1 ULS verification shall be demonstrated for hazardous events with intensity S in accordance
NC a,ALE
with 6.3.2.
6.3.2 The annual probability of the structure exceeding the ULS (defined in 6.2.1) shall not be larger
NC
than the value of P listed in Table 1.
f
Table 1 — Maximum tolerable annual probability of exceeding P
f
Consequence level P
f
-4
L1 4 × 10 = 1/2 500
-3
L2 1 × 10 = 1/1 000
-3
L3 2,5 × 10 = 1/400
NOTE 1 P values in Table 1 account for epistemic uncertainty due to the use of the mean hazard curve and the
f
mean fragility curve in Clause 9.
NOTE 2 Reference [22] describes the calibration of the simplified procedure in Clause 8 to the probabilities listed in
Table 1.
6.3.3 The maximum tolerable annual probability of exceeding the ULS may be less than listed in Table 1
NC
if specified by the operator or regulator, provided the structural response with probability of exceedance in
Table 1 is also demonstrated to be acceptable.
NOTE The lower probability event with its higher motions can result in nonlinear soil response which can
effectively reduce seismic demands on the structure.
−4
EXAMPLE 1 × 10 p.a. (1/10 000) for L1 facilities.
6.3.4 ULS verification shall be demonstrated for hazardous events with intensity S in accordance
DL a,ELE
with 6.3.5.
6.3.5 The annual probability of the structure exceeding the ULS , as defined in 6.2.2, shall not be larger
DL
than P or P as listed in Table 2.
ELE
ULS
DL
Table 2 — Maximum tolerable annual probability of exceeding ULS
DL
Consequence level
P
P
ULS ELE
DL
-3
L1 5,0 × 10 = 1/200 P is the annual probability of
ELE
exceedance of the spectral accel-
-2
L2 1,0 × 10 = 1/100
eration value, S given by the
a,ELE
-2
L3 2,0 × 10 = 1/50
hazard curve in Figure 6.
6.4 Seismic risk category
6.4.1 The facility shall be assigned a seismic risk category (SRC) in accordance with Table 3.
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 (PSHA).
Table 3 — Seismic risk category
Consequence level
S (1,0)
Site seismic
a,map
(see ISO 19900)
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
0,10 g to <0,25 g 2 SRC 4 SRC 2 SRC 2
0,25 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 facility with environmental consequence level greater than L3, shall
not be classified as consequence level L2 unless it is normally unoccupied (e.g. limited to inspection and
maintenance visits).
NOTE No reliable forewarning of seismic actions is feasible and, consequently, it is not possible to evacuate prior
to an earthquake.
6.5 ULS verification (using hazardous events with intensity = S )
DL a,ELE
6.5.1 S shall be determined in accordance with Clause 8 or Clause 9, depending on the SRC (described
a,ELE
in 6.4).
6.5.2 ULS limit state verification shall be performed using:
DL
a) actions arising from ground motion time histories where each ground motion has a spectral acceleration,
at the first lateral sway period of the structure, defined by S , see Clause 7;
a,ELE
b) representative capacities of members, joints, piles and soil, as defined in ISO 19900.
NOTE For fixed steel structures, ULS verification of the structure is demonstrated if ISO 19902:2020,
DL
Formulae (11.5-1) and (11.5-2) are satisfied.
6.6 ULS verification (using hazardous events with intensity = S )
NC a,ALE
6.6.1 S shall be determined in accordance with Clause 8 or Clause 9, depending on the SRC (described
a,ALE
in 6.4).
6.6.2 ULS limit state verification shall be performed using:
NC
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 ;
a,ALE
b) mean capacities of members, joints, piles, and soil (by use of mean yield stress, mean component
capacities and expected soil capacity).
NOTE Clause 7 provides analysis types and requirements to determine the above actions.
6.7 Seismic design procedure
6.7.1 Seismic design shall follow the limit state verification methods in 6.8 and be based on one of the
following design strategies:
a) a linear strength-based design strategy (with implied ductility);
b) a nonlinear (explicit) ductility-based design strategy.
NOTE A.6.7 provides detailed descriptions of the above strategies.
6.8 Methods for limit state verification
6.8.1 Limit state verification methods depend on the SRC as described in 6.8.2 to 6.8.6.
NOTE The provisions in this subclause are summarised in Table 4.

Table 4 — Summary of requirements for ULS verification
NC
Procedure for determining
Structural analysis
SRC Hazard analysis
S and S
RSA, NTHA or NPA
aE, LE aA, LE
1 None None required None required
ISO maps or regional information
RSA recommended Simplified (Clause 8) recommended
recommended
Site-specific PSHA permitted RSA recommended Simplified (Clause 8) recommended
complementary DSHA permitted NTHA or NPA permitted Detailed (Clause 9) permitted
Site-specific PSHA required NTHA recommended
3 Detailed (Clause 9) required
complementary DSHA permitted NPA permitted
Site-specific PSHA required
4 NTHA required Detailed (Clause 9) required
complementary DSHA permitted
6.8.2 Limit state verification of facilities classed as SRC 4:
a) shall perform the hazard analysis using PSHA in accordance with 9.1;
b) may perform a complementary hazard analysis using DSHA in accordance with 9.2;
c) shall determine S for ULS verification using the C method in accordance with 9.4;
a,ALE NC
c
d) shall perform the structural response analysis for the ULS by NTHA in accordance with 7.2;
NC
e) shall determine the structural response for verification of the ULS by either:
DL
1) linear time history analysis in accordance with 7.2; or
2) RSA in accordance with 7.1.
6.8.3 Limit state verification of facilities classed as SRC 3:
a) shall perform the hazard analysis using PSHA in accordance with 9.1;
b) may perform a complementary hazard analysis using DSHA in accordance with 9.2;
c) shall determine S for ULS verification using C in accordance with 9.4;
a,ALE NC
c
d) should perform the structural response analysis for the ULS by NTHA in accordance with 7.2;
NC
e) may perform structural response analysis for the ULS by NPA in accordance with 7.3;
NC
NOTE NTHA better simulates double hinging of piles in soft soils compared to NPA.
f) shall determine the structural response for limit state verification of the ULS by either:
DL
1) linear time history analysis in accordance with 7.2; or
2) response spectrum analysis in accordance with 7.1.
6.8.4 Limit state verification of facilities classed as SRC 2:
a) should perform the hazard analysis with the seismic maps and site correction factors in accordance
with 8.2 to 8.4;
b) may perform the hazard analysis with a PSHA in accordance with 9.1;
NOTE The simplified seismic action procedure is typically more conservative than the equivalent detailed
seismic action procedure.
c) may perform a complementary hazard analysis using DSHA in accordance with 9.2;

d) shall determine S for verification (for ULS ) by either:
a,ALE NC
1) the C method in accordance with 9.4; or
c
2) the N scale factor method in accordance with 8.5 to 8.8;
ALE
NOTE A 1 000-year uniform hazard spectrum can be produced in accordance with 9.1 rather than the 1 000-
year design response spectrum produced in accordance with 8.5 to 8.8.
f) shall determine the structural response for verification of the ULS by either:
DL
1) linear time history analysis in accordance with 7.2; or
2) RSA in accordance with 7.1.
f) shall determine the structural response for verification of the ULS by any of the following:
NC
1) RSA in accordance with 7.1;
2) NTHA in accordance with 7.2;
3) NPA in accordance with 7.3.
6.8.5 Limit state verification of facilities classed as SRC 1 may be performed but is not required.
6.8.6 For facilities classed as SRC >1, the risks arising due to collapse of the facility in seismic hazardous
events shall be minimised in accordance with ISO 19902 for ductile design of the primary structure and
joints.
7 Analysis types for structural response
7.1 Response spectrum analysis
7.1.1 Combination of modal responses shall be performed by the complete quadratic combination.
7.1.2 Directional responses for both horizontal directions and the vertical direction shall be determined.
7.1.3 Combination of directional responses:
a) should be performed by the square root of the sum of the squares;
b) may be performed by linear combination.
NOTE 1 Linear combination can be applied by taking one component at its maximum and the other two components
at 40 % of their respective maximum values (with the sign of each response parameter selected to maximise the
response combination) - see Reference [23].
[24]
NOTE 2 Linear combination is always more conservative than the square root of the sum of the squares .
7.1.4 The number of modes used in a RSA shall be the number of modes to achieve at least 90 % mass
participation in each horizontal direction.
[19]
NOTE ASCE 7-22 provides guidance on achieving 90 % mass participation.
7.1.5 RSA shall not be used if seismic isolation or passive energy dissipation devices are employed.
7.1.6 Linearized foundation stiffness values shall be based upon the magnitude of soil deformations
resulting from ground motions with spectral accelerations of S and S .
a,ELE a,ALE
7.1.7 Damping values shall be based upon deformation magnitudes resulting from ground motions with
spectral accelerations of S and S .
a,ELE a,ALE
7.1.8 Damping values should be based on recommendations in the Standard applicable to the structure
type, see Figure 1.
7.1.9 A damping ratio of 5 % may be used to represent structural and soil damping.
7.1.10 Larger values of damping due to hydrodynamics or soil deformation (hysteretic and radiation) may
be used provided the damping values used are substantiated.
7.2 Time history analysis
7.2.1 A minimum of 7 ground motion records shall be applied to the structure.
NOTE 1 Seven ground motion records applied in different orientations provide variability in the directional
response of the structure.
NOTE 2 If only 4 ground motion records are available for the site, then 4 additional records can be created by
exchanging the horizontal acceleration values.
7.2.2 The ground motion records for input to the time history analysis should be selected based on
deaggregation of the seismic hazard curve.
NOTE The structure’s response can be very different for two ground motion records having the same spectral
acceleration at the dominant period, typically the 1st sway modes i.e. S (T ), if the frequency contents for the two
a 1
records are sufficiently different. A large magnitude earthquake with a focus far from the site can have the same
S (T ) as a smaller magnitude earthquake with a focus close to the site, however the ground motion records for the
a 1
earthquake far from the site typically have less high frequency motions as they are attenuated by the larger site to
source distance.
7.2.3 Down-pile displacement time histories (derived from a DSRA) should be applied (in accordance with
Reference [25]), rather than applying near-surface displacement time histories uniformly from pile tip to
pile head.
7.2.4 Soil radiation damping should be represented in a nonlinear time history analysis in accordance
with IOGP S-631-11, A.11.6.4.
7.2.5 Ground motions may be scaled based on a conditional spectrum rather than the uniform hazard
spectrum.
7.2.6 Verification for the ULS by a linear time history analysis shall use a nonlinear soil model.
DL
7.2.7 Verification for the ULS shall be demonstrated when using the time history analysis, if utilisation
DL
ratios for all members and all joints are less than unity at each time step.
NOTE For verification of ULS the maximum member or joint utilization is determined during each time history
DL
record.
7.2.8 Time history analysis and the structural nonlinear model for the hazardous event actions for the
ULS shall be in accordance with the criteria specified in ISO 19902 and IOGP S-631-11.
NC
7.2.9 ULS verification of the structure shall be deemed to have been demonstrated provided that no
NC
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 NTHA.
a,ALE
NOTE For verification, if no more than 3 of the 7-time histories analysis result in collapse of the structure then
P is no greater than 1 divided by the return period for the spectral acceleration associated with T of the
dom
ULS
NC
7-time history events.
7.2.10 Time history analysis shall be used to obtain deck motions and deck motion response spectra used
for design of large topside appurtenances with complex dynamic response (such as drill rigs, flare booms).
NO
...

ISO/TC 67/SC 7
Date: 2025-09-30
ISO/TC 67/SC 7
Secretariat: BSI
Date: 2026-02-18
Oil and gas industries including lower carbon energy —
Specific requirements for offshore structures — Part 2:
Seismic design procedures and criteria
Part 2:
Seismic design procedures and criteria
Industries pétrolièresdu pétrole et gazièresdu gaz, y compris les énergies à faible émission deteneur
en carbone — Exigences spécifiques relatives aux structures en mer —
Partie 2: Procédures de conception sismique et critères sismiques
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FDIS stage
ISO 19901-2:2025(E)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this
publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical,
including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can
be requested from either ISO at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel.Phone: + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ISO/FDIS 19900:2019(E)
Contents
Foreword . 6
Introduction. 7
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
4.1 Symbols . 4
4.2 Abbreviated terms . 5
5 Seismic hazards . 6
6 Performance objectives and limit states. 6
6.1 General . 6
6.2 Ultimate limit states . 9
6.3 Performance objectives . 10
6.4 Seismic risk category . 11
6.5 ULSDL verification (using hazardous events with intensity = Sa,ELE) . 12
6.6 ULS verification (using hazardous events with intensity = S ) . 12
NC a,ALE
6.7 Seismic design procedure . 12
6.8 Methods for limit state verification . 13
7 Analysis types for structural response . 14
7.1 Response spectrum analysis . 14
7.2 Time history analysis . 15
7.3 Nonlinear pushover analysis. 16
8 Simplified procedure for determining S and S . 17
a,ELE a,ALE
8.1 General . 17
8.2 Spectral accelerations . 17
8.3 Site class . 17
8.4 Site correction factor coefficients . 19
8.5 1 000-year horizontal acceleration spectrum . 20
8.6 1 000-year vertical acceleration spectrum . 22
8.7 Damping adjustment . 23
8.8 Determining S and S . 24
a,ELE a,ALE
9 Detailed procedure for determining S and S . 25
a,ELE a,ALE
9.1 Probabilistic seismic hazard analysis . 25
9.2 Deterministic seismic hazard analysis . 28
9.3 Determining 𝑪𝑪𝑪𝑪 . 28
9.4 Determining S and S . 31
a,ELE a,ALE
9.5 Dynamic site response analysis . 32
10 Floating structures . 33
Annex A (informative) Additional information and guidance . 34
Annex B (normative) Seismic maps with spectral accelerations for simplified action
procedure . 50
Annex C (normative) Regional information . 154
Bibliography . 160
CCoonfnfiiddeentntiiaall
4 © ISO 2019 – All rights reserved

ISO 19901-2:2025(E)
ISO/FDIS 19900:2019(E)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of
(a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received notice
of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
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 third edition (ISO 19901-2:2022), which has been technically
revised.
The main changes are as follows:
— — the scope has been expanded to cover offshore wind and other renewable energy offshore
structures;
— — requirements from common industry specifications (IOGP JIP 35) have been incorporated;
— — the seismic hazard maps have been updated.
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.
CCoonfnfiiddeentntiiaall
6 © ISO 2019 – All rights reserved

ISO 19901-2:2025(E)
Introduction
The International Standards for offshore structures prepared by ISO TC 67/SC 7 comprise:
— ISO 19900, the unifying International Standard for offshore structures.;
— the ISO 19901 series, providing specific requirements for offshore structures.;
— ISO 19902, ISO 19903, ISO 19904-1, the ISO 19905 series and ISO 19906, “structure type” standards.
Figure 1NOTE These are collectively referred to as the “ISO 19900 suite” for offshore structures.
Figure 1 illustrates the relationships between the standards in the ISO 19900 suiteInternational
Standards for offshore structures prepared by ISO TC 67/SC 7.

ISO/FDIS 19900:2019(E)
Figure 1 — Relationship of International Standards for offshore structures prepared by
ISO/TC 67/SC 7
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. Additional information and guidance are given in Annex AAnnex A,, where the clause
numbering mirrors the normative clauses to facilitate cross referencing.
In ISO International Standards, the following verbal forms are used:
— — “shall” and “shall not” are used to indicate requirements strictly to be followed in order to
conform to the document and from which no deviation is permitted;
— — “should” and “should not” are used to indicate that, among several possibilities, one is
recommended as particularly suitable, without mentioning or excluding others, or that a certain
course of action is preferred but not necessarily required, or that (in the negative form) a certain
possibility or course of action is deprecated but not prohibited;
— — “may” is used to indicate a course of action permissible within the limits of the document;
— — “can” and “cannot” are used for statements of possibility and capability, whether material,
physical or causal.
CCoonfnfiiddeentntiiaall
8 © ISO 2019 – All rights reserved

ix
DRAFT International Standard
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 requirements for seismic design and assessment of offshore structures.
This document includes recommendations for the effects of seismic events on floating structures.
This document addresses specifically the design and assessment of offshore structures subjected to
earthquake-induced ground motions. It also covers briefly other geologically induced hazards such as
liquefaction, slope instability, fault surface displacement, tsunamis, mud volcanoes and shock waves.
This document provides requirements for site-specific probabilistic seismic hazard analysis for offshore
structures in high seismic areas and for offshore structures with high consequence levels.
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
ISO 19902, OilPetroleum and natural gas industries including lower carbon energy — Fixed steel offshore
structures
IOGP S-631-11, Supplementary Specification for Fixed Steel Offshore Structures, International Oil & Gas
Producers Association, Version 2, 8 February 2021
3 Terms and definitions
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 3.1
abnormal level earthquake
ALE
) due to a rare intense earthquake with a very low probability of occurrence during the life
ground motion (3.6
of the structure
Confidential
ISO/FDIS 19900:2019(E 19901-2:2026(en)
Note 1 to entry: Typically, having an annual probability of exceedance (3.10) of one in a few thousand years.
3.2 3.2
active fault
fault likely to have another earthquake in the future
3.3 3.3
attenuation
decay of seismic waves as they travel from the earthquake source to the site under consideration
3.4 3.4
deaggregation
separation of seismic hazard contributions from different faults and seismic source zones
3.5 3.5
extreme level earthquake
ELE
ground motion (3.6) due to an earthquake with a reasonable probability of occurring during the life of the
structure
Note 1 to entry: Typically having an annual probability of exceedance (3.10) of one in a few hundred years.
3.6 3.6
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 and consequently only seabed motions or
motions along the length of piles 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.
3.7 3.7
liquefaction
fluidity of soil due to the increase in pore pressures caused by earthquake action under undrained conditions
3.8 3.8
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.
3.9 3.9
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 (3.6(3.6)) characteristics
3.10 3.10
probability of exceedance
P
e
probability that a variable (or an event) exceeds a specified reference level within a given exposure period
EXAMPLE The annual probability of exceedance of a specified magnitude of ground acceleration, ground velocity or
ground displacement.
3.11 3.11
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
3.12 3.12
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
3.13 3.13
safety system
system provided on the offshore structure to detect, control and mitigate hazardous situations
EXAMPLE Gas detection, emergency shutdown, fire protection, and their control systems.
3.14 3.14
seabed slide
failure of seabed slopes
Note 1 to entry: The seabed is defined as the soil material below the sea floor [SOURCE: (ISO 19900:2019, 3.47].).
Note 2 to entry: The effective seabed is defined in 8.3.28.3.2;; typically, being the upper 30 m of seabed material.
3.15 3.15
seismic hazard curve
curve showing the annual probability of exceedance (3.10(3.10)) against a measure of ground motion (3.6(3.6))
or response of the single degree of freedom oscillator
Note 1 to entry: The seismic measures can include parameters such as peak ground acceleration, spectral acceleration
(3.19(3.19),), spectral velocity or spectral displacement.
3.16 3.16
seismic reserve capacity factor
C
r
factor indicating the structure’s ability to sustain ground motions (3.6(3.6)) due to earthquakes beyond the
level of the extreme level earthquake (3.5(3.5))
3.17 3.17
seismic risk category
SRC
category defined from the consequence level and the intensity of seismic motions
3.18 3.18
site response analysis
wave propagation analysis permitting the evaluation of the effect of local geological and soil conditions on the
ground motions (3.6(3.6)) as they propagate up from depth to the surface at the site
ISO/FDIS 19900:2019(E 19901-2:2026(en)
3.19 3.19
spectral acceleration
maximum acceleration response of a single degree of freedom oscillator subjected to ground motions
(3.6(3.6)) due to an earthquake
3.20 3.20
tsunami
long period sea waves caused by rapid vertical movements of the sea floor
Note 1 to entry: The vertical movement of the sea floor is often associated with fault rupture during earthquakes or with
seabed slides (3.14(3.14).).
3.21 3.21
zero pad
a technique used in signal processing particularly when analysing earthquake recordings using the Fastfast
Fourier Transformationtransformation
4 Symbols and abbreviated terms
4.1 Symbols
a tail slope of the seismic hazard curve
R
C correction factor for the acceleration part (shorter periods) of a response spectrum
a
C correction factor applied to the spectral acceleration to account for uncertainties not
c
captured in a seismic hazard curve
C seismic reserve capacity factor
r
Cv correction factor for the velocity part (longer periods) of a response spectrum
d thickness of soil layer
D scaling factor for damping
G initial (small strain) shear modulus of the soil
max
g acceleration due to gravity
H horizontal spectral accelerations
M magnitude of an earthquake measured by the energy released at its source
NALE scale factor for conversion of the site 1 000-year acceleration spectrum to the site ALE
acceleration spectrum
p atmospheric pressure
a
PALE annual probability of exceedance for the ALE event
P annual probability of exceedance for the ELE event
ELE
P annual probability of exceedance
e
𝑃𝑃 𝑃𝑃 annual probability of exceeding the ULSDL
ULS ULS
DL DL
𝑃𝑃 𝑃𝑃 annual probability of exceeding the ULSNC
ULS ULS
NC NC
q cone penetration resistance of soil
c
𝑞𝑞 𝑞𝑞 normalized cone penetration resistance of soil
cl cl
𝑞𝑞̄𝑞𝑞¯ average normalized cone penetration resistance of sand in the effective seabed
cl cl
R representative capacity
k
S (T) spectral acceleration (associated with single degree of freedom oscillator period, T)
a
Sa,ALE(T) ALE spectral acceleration
S (T ) ALE spectral acceleration at T
a,ALE dom dom
S (T) ELE spectral acceleration
a,ELE
S (T ) ELE spectral acceleration at T
a,ELE dom dom
Sa,map(T) 1 000-year bedrock spectral acceleration obtained from seismic maps
S (T) site spectral acceleration corresponding to a return period of 1 000 years
a,site
̅¯
𝑆𝑆 (𝑇𝑇)𝑆𝑆 (𝑇𝑇) spectral acceleration having an annual probability of exceedance (P ) obtained from a
e
a,𝑃𝑃 a,𝑃𝑃
e e
PSHA.
𝑆𝑆 (𝑇𝑇 )𝑆𝑆 site-spec ific spectral acceleration at T having an annual probability 𝑃𝑃 𝑃𝑃 of
dom
a,𝑃𝑃 dom a,𝑃𝑃 ULS ULS
ULS ULS DL DL
DL
exceeding the ULSDL
𝑆𝑆 (𝑇𝑇 )𝑆𝑆 site-spec ific spectral acceleration at T having an annual probability 𝑃𝑃 𝑃𝑃 of
dom
a,𝑃𝑃 dom a,𝑃𝑃 ULS ULS
ULS ULS NC NC
NC
exceeding the ULS
NC
su undrained shear strength of the soil
s̅ average undrained shear strength of the soil in the effective seabed
u
T natural period of a simple, single degree of freedom oscillator
Tdom dominant modal period of the structure
T return period
return
V vertical spectral accelerations
𝑣𝑣𝑣𝑣 representative shear wave velocity
s s
𝑣𝑣̅𝑣𝑣¯ s average 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′v0 in situ vertical effective stress of soil
4.2 Abbreviated terms
DL damage limitation state (specified in 6.2.36.2.3 and 6.2.46.2.4))
DSHA deterministic seismic hazard analysis
DSRA dynamic site response analysis
L1, L2, L3 consequence levels (see ISO 19900)
NC near collapse state (specified in 6.2.16.2.1 and 6.2.26.2.2))
NPA nonlinear pushover analysis
NTHA nonlinear time history analysis
RSA response spectrum analysis
ISO/FDIS 19900:2019(E 19901-2:2026(en)
SDOFS single degree of freedom
SLS serviceability limit state
SPA static pushover analysis
ULS ultimate limit state
5 Seismic hazards
5.1 5.1 Seismic design and assessment of offshore structures shall include the effect of ground motions
due to earthquakes.
5.2 5.2 In addition to the effect of ground motion, 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) a) soil liquefaction,
b) b) seabed slide,
c) c) fault surface displacement,
d) d) tsunamis,
e) e) mud volcanoes,
f) f) velocity pulse from directivity effects (earthquake-induced shock wave in the water column
typically associated with volcanic eruptions).
NOTE Provisions for seismic design and assessment of floating structures is covered in Clause 10.
6 Performance objectives and limit states
6.1 General
6.1.1 6.1.1 The risks, due to the structure being exposed to seismic hazardous events, shall be
demonstrated to be tolerable by stake holders in accordance with 6.1.26.1.2 to 6.1.5.
NOTE The requirements in this document ensure that the structure has 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 seismic hazard curve for the site.
6.1.2 6.1.2 Demonstration that the structure meets the performance objectives shall be by limit state
verification in accordance with ISO 19900.
6.1.3 6.1.3 The performance objective for life-safety and environmental risks, typically associated with an
ALE, shall specify the maximum tolerable annual probability that the (damaged) state of structure can
exceed ULS .
NC
NOTE 1 Life-safety risk refers to the potential for injury or loss of life during an earthquake.
NOTE 2 ULSNC is described in 6.2.16.2.1. When the state of the structure exceeds ULSNC one or more components can
have failed and the structure can be near to collapsing.
6.1.4 6.1.4 The performance objective for business-disruption risk, typically associated with an ELE, shall
specify the maximum tolerable annual probability that the (damaged) state of structure can exceed
ULS .
DL
NOTE ULSDL is described in 6.2.26.2.2. When the state of the structure exceeds ULSDL, the structural system remains
stable, but the lateral system of the structure (braces, joints, and piles) can have plastic strains that result in permanent
deformation that can affect the functionality of the structure. The permanent deformation is likely repairable and thus
the functionality of the facility can be restored.
ISO/FDIS 19900:2019(E 19901-2:2026(en)

a
SRC 2 structures can alternatively be designed using the detailed seismic action procedure similar to SRC 3 and SRC 4 structures
(see Table 4Table 4)).
Figure 2 — Steps for limit state verification
6.2 Ultimate limit states
6.2.1 6.2.1 The state of the structure at the ULSNC, typically due to hazardous events with intensity Sa,ALE(T),
shall not include:
a) collapse of the structure’s gravity load resisting system (i.e.,. legs, pile to leg joints, pile-soil resistance) or
collapse of the gravity sub-system that supports the living quarters;
ISO/FDIS 19900:2019(E 19901-2:2026(en)
b) damage to safety systems, escape routes, and evacuation systems that prevent their functionality;
c) loss of supports for critical hydrocarbon equipment that could lead to escalation by loss of process
containment;
d) collapse of the living quarters, masts, derricks, flare structures and other safety critical structures.
6.2.2 6.2.2 The state of the structure at the ULS may include damage to the structure’s lateral system
NC
(i.e.,. braces and their joints, and pile lateral deformation) as follows:
a) severed braces (by fracture or low-cycle fatigue, with or without strain ratcheting);
b) plastic local buckling of braces or global buckling of braces;
c) permanent deformation of joints, and collapse or fracture of joints;
d) permanent lateral deformation of piles;
e) spalling of reinforced concrete.
6.2.3 6.2.3 The state of the structure at the ULS , typically due to hazardous events with intensity S ,
DL a,ELE
shall not include:
a) a) permanent deformation of the components comprising the structure’s gravity load resisting
system (i.e.,. legs, pile to leg joints, and pile-soil resistance);
b) b) permanent deformation to the components comprising the structure’s lateral system (i.e.
braces and their joints, and pile lateral deformation);
c) c) damage to safety systems, escape routes, and evacuation systems that prevent their
functionality;
d) d) damage to pipelines, conductors, risers, and other safety-critical components due to
displacements at mudline elevation of the structure;
e) e) damage due to toppling of topsides equipment and cable trays;
f) f) damage to masts, derricks, and flare structures;
g) g) damage to sliding supports that prevent their functionality;
h) h) damage to piping systems that prevents their functionality due to differential displacement of
supports.
6.2.4 6.2.4 The state of the structure at the ULS should not include damage that will result in dropped
DL
objects.
6.3 Performance objectives
6.3.1 6.3.1 ULS verification shall be demonstrated for hazardous events with intensity S in
NC a,ALE
accordance with 6.3.26.3.2.
6.3.2 6.3.2 The annual probability of the structure exceeding the ULSNC (defined in 6.2.16.2.1)) shall not
be larger than the value of 𝑷𝑷 listed in Table 1Table 1.
𝒇𝒇
Table 1 — Maximum tolerable annual probability of exceeding 𝑷𝑷𝑷𝑷
𝒇𝒇 𝒇𝒇
𝑷𝑷𝑃𝑃
Consequence level
𝒇𝒇 𝑓𝑓
-4
L1 4 × 10 = 1/2 500
-3
L2 1 × 10 = 1/1 000
-3
L3 2,5 × 10 = 1/400
NOTE 1 𝑃𝑃 values in Table 1Table 1 account for epistemic uncertainty due to the use of the mean hazard curve and the
𝑓𝑓
mean fragility curve in Clause 9Clause 9.
NOTE 2 Reference [22] [22] describes the calibration of the simplified procedure in Clause 8Clause to the probabilities
listed in Table 1Table 1.
6.3.3 6.3.3 The maximum tolerable annual probability of exceeding the ULSNC may be less than listed in
Table 1Table 1 if specified by the operator or regulator, provided the structural response with
probability of exceedance in Table 1Table 1 is also demonstrated to be acceptable.
NOTE The lower probability event with its higher motions can result in nonlinear soil response which can effectively
reduce seismic demands on the structure.
−4
EXAMPLE 1 × 10 p.a. (1/10 000) for L1 facilities.
6.3.4 6.3.4 ULS verification shall be demonstrated for hazardous events with intensity S in
DL a,ELE
accordance with 6.3.56.3.5.
6.3.5 6.3.5 The annual probability of the structure exceeding the ULS , as defined in 6.2.26.2.2,, shall not
DL
be larger than P or 𝑷𝑷 𝑷𝑷 as listed in Table 2Table 2.
ELE
𝐔𝐔𝐔𝐔𝐔𝐔 ULS
𝐃𝐃𝐔𝐔 DL
Table 2 — Maximum tolerable annual probability of exceeding ULS
DL
Consequence level 𝑷𝑷 𝑃𝑃
PELE
𝐔𝐔𝐔𝐔𝐔𝐔 𝑈𝑈𝑈𝑈𝑆𝑆
𝐃𝐃𝐔𝐔 𝐷𝐷𝐷𝐷
-3
L1 5,0 × 10 = 1/200 P is the annual probability of
ELE
exceedance of the spectral
-2
L2 1,0 × 10 = 1/100
acceleration value, S given by
a,ELE
the hazard curve in
-2
L3 2,0 × 10 = 1/50
Figure 6Figure 7.
6.4 Seismic risk category
6.4.1 6.4.1 The facility shall be assigned a seismic risk category (SRC) in accordance with Table 3Table 3.
6.4.2 6.4.2 Site seismic zone shall be determined from the 1,0 s horizontal spectral acceleration maps in
Annex BAnnex B or from a site-specific seismic hazard study (PSHA).
Table 3 — Seismic risk category
Consequence level
S (1,0)
a,map
Site seismic
(see ISO 19900)
(see
zone
Annex BAnnex 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
ISO/FDIS 19900:2019(E 19901-2:2026(en)
Consequence level
S (1,0)
a,map
Site seismic
(see ISO 19900)
(see
zone
Annex BAnnex B))
L1 L2 L3
0,10 g to <0,25 g 2 SRC 4 SRC 2 SRC 2
0,25 g to <0,45 g 3 SRC 4 SRC 3 SRC 2
4 SRC 4 SRC 4 SRC 3
≥≥0,45 g
6.4.3 6.4.3 For seismic design situations, a facility with environmental consequence level greater than L3,
shall not be classified as consequence level L2 unless it is normally unoccupied (e.g.,. limited to
inspection and maintenance visits).
NOTE No reliable forewarning of seismic actions is feasible and, consequently, it is not possible to evacuate prior to
an earthquake.
6.5 ULS verification (using hazardous events with intensity = S )
DL a,ELE
6.5.1 6.5.1 Sa,ELE shall be determined in accordance with Clause 8Clause or Clause 9Clause , depending
on the SRC (described in 6.4).
6.5.2 6.5.2 ULS limit state verification shall be performed using:
DL
a) a) actions arising from ground motion time histories where each ground motion has a spectral
acceleration, at the first lateral sway period of the structure, defined by S , see Clause Clause 7;
a,ELE
Field Code Changed
b) b) representative capacities of members, joints, piles and soil, as defined in ISO 19900.
NOTE For fixed steel structures, ULSDL verification of the structure is demonstrated if ISO 19902:2020,
Formulae (11.5-1) and (11.5-2) are satisfied.
6.6 ULS verification (using hazardous events with intensity = S )
NC a,ALE
6.6.1 6.6.1 S shall be determined in accordance with Clause 8Clause or Clause 9Clause , depending
a,ALE
on the SRC (described in 6.4).
6.6.2 6.6.2 ULS limit state verification shall be performed using:
NC
a) 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 ;
a,ALE
b) b) mean capacities of members, joints, piles, and soil (by use of mean yield stress, mean
component capacities and expected soil capacity).
NOTE Clause 7 1 Clause provides analysis types and requirements to determine the above actions.
6.7 Seismic design procedure
6.7.1 6.7.1 Seismic design shall follow the limit state verification methods in 6.8 and be based on one of
the following design strategies:
a) a linear strength-based design strategy (with implied ductility);
b) a nonlinear (explicit) ductility-based design strategy.
NOTE A.6.7 provides detailed descriptions of the above strategies.
6.8 Methods for limit state verification
6.8.1 6.8.1 Limit state verification methods depend on the SRC as described in 6.8.2 to 6.8.6below.
NOTE The provisions in this clausesubclause are summarised in Table 4Table 4.
Table 4 — Summary of requirements for ULS verification
NC
Structural analysis
Procedure for determining
SRC Hazard analysis
𝑆𝑆 and 𝑆𝑆
RSA, NTHA or NPA 𝑎𝑎,𝐸𝐸𝑈𝑈𝐸𝐸 𝑎𝑎,𝐴𝐴𝑈𝑈𝐸𝐸
1 None None required None required
ISO maps or regional information Simplified (Clause 8(clause 8))
RSA recommended
recommended recommended
Simplified (Clause 8(clause 8))
Site-specific PSHA permitted RSA recommended
recommended
complementary DSHA permitted NTHA or NPA permitted
Detailed (Clause 9(clause 9)) permitted
Site-specific PSHA required NTHA recommended
3 Detailed (Clause 9(clause 9)) required
complementary DSHA permitted NPA permitted
Site-specific PSHA required
4 NTHA required Detailed (Clause 9(clause 9)) required
complementary DSHA permitted
6.8.2 6.8.2 Limit state verification of facilities classed as SRC 4:
a) a) shall perform the hazard analysis using PSHA in accordance with 9.1;
b) b) may perform a complementary hazard analysis using DSHA in accordance with 9.2;
c) c) shall determine Sa,ALE for ULSNC verification using the 𝐶𝐶𝐶𝐶 method in accordance with 9.4;
c c Field Code Changed
d) d) shall perform the structural response analysis for the ULSNC by NTHA in accordance with 7.2;
e) e) shall determine the structural response for verification of the ULS by either:
DL
1) 1) linear time history analysis in accordance with 7.2; or
2) 2) RSA in accordance with 7.1.
6.8.3 6.8.3 Limit state verification of facilities classed as SRC 3:
a) a) shall perform the hazard analysis using PSHA in accordance with 9.1;
b) b) may perform a complementary hazard analysis using DSHA in accordance with 9.2;
c) c) shall determine S for ULS verification using 𝐶𝐶𝐶𝐶 in accordance with 9.4;
a,ALE NC
c c
d) d) should perform the structural response analysis for the ULS by NTHA in accordance with 7.2;
NC
e) e) may perform structural response analysis for the ULS by NPA in accordance with 7.3;
NC
NOTE NTHA better simulates double hinging of piles in soft soils compared to NPA.
ISO/FDIS 19900:2019(E 19901-2:2026(en)
f) f) shall determine the structural response for limit state verification of the ULSDL by either:
1) 1) linear time history analysis in accordance with 7.2,; or
2) 2) response spectrum analysis in accordance with 7.1.
6.8.4 6.8.4 Limit state verification of facilities classed as SRC 2:
a) a) should perform the hazard analysis with the seismic maps and site correction factors in
accordance with 8.2 to 8.4;
b) b) may perform the hazard analysis with a PSHA in accordance with 9.1;
NOTE The simplified seismic action procedure is typically more conservative than the equivalent detailed
seismic action procedure.
c) c) may perform a complementary hazard analysis using DSHA in accordance with 9.2;
d) d) shall determine S for verification (for ULS ) by either:
a,ALE NC
1) 1) the 𝐶𝐶𝐶𝐶 method in accordance with 9.4; or
c c
2) 2) the NALE scale factor method in accordance with 8.5 to 8.8;
NOTE A 1 000-year uniform hazard spectrum can be produced in accordance with 9.19.1 rather than the 1 000-
year design response spectrum produced in accordance with 8.5 to 8.8.
f) shall determine the structural response for verification of the ULS by either:
DL
1) 1) linear time history analysis in accordance with 7.2; or
2) 2) RSA in accordance with 7.1.
f) f) shall determine the structural response for verification of the ULSNC by any of the following:
1) 1) RSA in accordance with 7.1,;
2) 2) NTHA in accordance with 7.2,;
3) 3) NPA in accordance with 7.3.
6.8.5 6.8.5 Limit state verification of facilities classed as SRC 1 may be performed but is not required.
6.8.6 6.8.6 For facilities classed as SRC >1, the risks arising due to collapse of the facility in seismic
hazardous events shall be minimised in accordance with ISO 19902 for ductile design of the primary
structure and joints.
7 Analysis types for structural response
7.1 Response spectrum analysis
7.1.1 7.1.1 Combination of modal responses shall be performed by the complete quadratic combination.
7.1.2 7.1.2 Directional responses for both horizontal directions and the vertical direction shall be
determined.
7.1.3 7.1.3 Combination of directional responses:
a) a) should be performed by the square root of the sum of the squares,;
b) b) may be performed by linear combination.
NOTE 1 Linear combination can be applied by taking one component at its maximum and the other two components
at 40 % of their respective maximum values (with the sign of each response parameter selected to maximise the response
combination) - see Reference [23] [23]. .
[24][24]
NOTE 2 Linear combination is always more conservative than the square root of the sum of the squares .
7.1.4 7.1.4 The number of modes used in a RSA shall be the number of modes to achieve at least 90 %
mass participation in each horizontal direction.
[19] [19]
NOTE ASCE 7-22 provides guidance on achieving 90 % mass participation.
7.1.5 7.1.5 RSA shall not be used if seismic isolation or passive energy dissipation devices are employed.
7.1.6 7.1.6 LinearisedLinearized foundation stiffness values shall be based upon the magnitude of soil
deformations resulting from ground motions with spectral accelerations of S and S .
a,ELE a,ALE
7.1.7 7.1.7 Damping values shall be based upon deformation magnitudes resulting from ground motions
with spectral accelerations of S and S .
a,ELE a,ALE
7.1.8 7.1.8 Damping values should be based on recommendations in the Standard applicable to the
structure type, see Figure 1Figure 1.
7.1.9 7.1.9 A damping ratio of 5 % may be used to represent structural and soil damping.
7.1.10 7.1.10 Larger values of damping due to hydrodynamics or soil deformation (hysteretic and radiation)
may be used provided the damping values used are substantiated.
7.2 Time history analysis
7.2.1 7.2.1 A minimum of 7 ground motion records shall be applied to the structure.
NOTE 1 Seven ground motion records applied in different orientations provide variability in the directional response
of the structure.
NOTE 2 If only 4 ground motion records are available for the site, then 4 additional records can be created by
exchanging the horizontal acceleration values.
7.2.2 7.2.2 The ground motion records for input to the time history analysis should be selected based on
deaggregation of the seismic hazard curve.
NOTE The structure’s response can be very different for two ground motion records having the same spectral
acceleration at the dominant period, typically the 1st sway modes i.e.,. Sa(T1), if the frequency contents for the two records
are sufficiently different. A large magnitude earthquake with a focus far from the site can have the same S (T ) as a smaller
a 1
magnitude earthquake with a focus close to the site, however the ground motion records for the earthquake far from the
site typically have less high frequency motions as they are attenuated by the larger site to source distance.
7.2.3 7.2.3 Down-pile displacement time histories (derived from a DSRA) should be applied (in
accordance with Reference [[25] [25]),]), rather than applying near-surface displacement time
histories uniformly from pile tip to pile head.
ISO/FDIS 19900:2019(E 19901-2:2026(en)
7.2.4 7.2.4 Soil radiation damping should be represented in a nonlinear time history analysis in
accordance with IOGP S-631-11, A.11.6.4.
7.2.5 7.2.5 Ground motions may be scaled based on a conditional spectrum rather than the uniform
hazard spectrum.
7.2.6 7.2.6 Verification for the ULSDL by a linear time history analysis shall use a nonlinear soil model.
7.2.7 7.2.7 Verification for the ULSDL shall be demonstrated when using the time history analysis, if
utilisation ratios for all members and all joints are less than unity at each time step.
NOTE For verification of ULS the maximum member or joint utilization is determined during each time history
DL
record.
7.2.8 7.2.8 Time history analysis and the structural no
...

PROJET
Norme
internationale
ISO/DIS 19901-2
ISO/TC 67/SC 7
Industries du pétrole et du gaz, y
Secrétariat: BSI
compris les énergies à faible teneur
Début de vote:
en carbone — Exigences spécifiques
2024-11-11
relatives aux structures en mer —
Vote clos le:
2025-02-03
Partie 2:
Procédures de conception et
critères sismiques
Oil and gas industries including lower carbon energy — Specific
requirements for offshore structures —
Part 2: Seismic design procedures and criteria
ICS: 75.180.10
CE DOCUMENT EST UN PROJET DIFFUSÉ
POUR OBSERVATIONS ET APPROBATION. IL
EST DONC SUSCEPTIBLE DE MODIFICATION
ET NE PEUT ÊTRE CITÉ COMME NORME
INTERNATIONALE AVANT SA PUBLICATION EN
TANT QUE TELLE.
Le présent document est distribué tel qu’il est parvenu du secrétariat
du comité. OUTRE LE FAIT D’ÊTRE EXAMINÉS POUR
ÉTABLIR S’ILS SONT ACCEPTABLES À DES
FINS INDUSTRIELLES, TECHNOLOGIQUES ET
COMMERCIALES, AINSI QUE DU POINT DE VUE
DES UTILISATEURS, LES PROJETS DE NORMES
INTERNATIONALES DOIVENT PARFOIS ÊTRE
TRAITEMENT PARALLÈLE ISO/CEN
CONSIDÉRÉS DU POINT DE VUE DE LEUR
POSSIBILITÉ DE DEVENIR DES NORMES
POUVANT SERVIR DE RÉFÉRENCE DANS LA
RÉGLEMENTATION NATIONALE.
LES DESTINATAIRES DU PRÉSENT PROJET
SONT INVITÉS À PRÉSENTER, AVEC LEURS
OBSERVATIONS, NOTIFICATION DES DROITS
DE PROPRIÉTÉ DONT ILS AURAIENT
ÉVENTUELLEMENT CONNAISSANCE
ET À FOURNIR UNE DOCUMENTATION
EXPLICATIVE.
Numéro de référence
ISO/DIS 19901-2:2024(fr)
ISO/DIS 19901-2:2024(fr)
ISO/TC 67/SC 7
Date : 2024‐11‐11
ISO/DIS 19901‐2:2024(fr)
ISO/TC 67/SC 7
Secrétariat : BSI
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
Oil and gas industries including lower carbon energy — Specific requirements for offshore structures —
Part 2: Seismic design procedures and criteria

ICS : 75.180.10
DOCUMENT PROTÉGÉ PAR COPYRIGHT
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publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,
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ii
ISO/DIS 19901‐2:2024(fr)
Sommaire Page
Avant‐propos . v
Introduction . vii
1  Domaine d'application . 1
2  Références normatives . 1
3  Termes et définitions (En suspens) . 1
4  Symboles et abréviations (En suspens) . 4
4.1  Symboles . 4
4.2  Abréviations . 6
5  Aléas sismiques . 6
6  Objectifs de performance, états limites et états d'endommagement . 7
6.1  Généralités . 7
6.2  États limites et états d'endommagement . 9
6.3  Objectifs de performance . 11
6.4  Catégorie de risque sismique . 11
6.5  Vérification à l'état limite DL (utilisation d'événements dangereux ayant une
intensité = S ) . 12
aE, LE
6.6  Vérification à l'état limite NC (utilisation d'événements dangereux ayant une
intensité = S ) . 12
aA, LE
6.7  Procédure de conception . 13
6.8  Méthodes de vérification aux états limites . 16
6.8.1  Généralités . 16
6.8.2  Méthodes de vérification aux états limites . 16
7  Types d'analyse pour la réponse structurelle . 19
7.1  Analyse de la réponse spectrale . 19
7.2  Analyse faisant appel aux fonctions temporelles . 20
7.3  Analyse non linéaire en poussée progressive . 21
8  Procédure simplifiée de détermination de S et de S . 22
aE, LE aA, LE
8.1  Généralités . 22
8.2  Accélérations spectrales . 22
8.3  Classe de site . 22
8.4  Coefficients de correction du site . 23
8.5  Spectre d'accélération horizontale sur 1 000 ans . 25
8.6  Spectre d'accélération verticale sur 1 000 ans . 26
8.7  Ajustement de l'amortissement . 27
8.8  Détermination de S et de S . 28
aE, LE aA, LE
9  Procédure détaillée de détermination de S et de S . 29
aE, LE aA, LE
9.1  Analyse probabiliste de l'aléa sismique (PSHA) . 29
9.2  Analyse déterministe de l'aléa sismique (DSHA) . 31
9.3  Analyse dynamique de la réponse du site (DSRA) . 32
9.4  Détermination de C . 32
c
iii
ISO/DIS 19901‐2:2024(fr)
9.5  Détermination de S et de S . 34
aE, LE aA, LE
10  Structures flottantes . 35
10.1  C est soit mal défini, soit inconnu . 35
r
10.2  Effets des ondes de choc . 35
10.3  ELE (contrôle de l'ULS) . 36
Annex A (informative) Additional information and guidance . 37
Annex B (informative) Simplified action procedure spectral accelerations . 49
Annexe C (normative) Informations régionales .103
Bibliographie .109

iv
ISO/DIS 19901‐2:2024(fr)
Avant‐propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux
de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général
confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire
partie du comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (IEC) en ce qui concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont décrites
dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents critères
d'approbation requis pour les différents types de documents ISO. Le présent document a été rédigé
conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2
(voir www.iso.org/directives).
L'attention est attirée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable de ne
pas avoir identifié tout ou partie de tels droits de brevet. Les détails concernant les références aux droits de
propriété intellectuelle ou autres droits analogues identifiés lors de l'élaboration du document sont indiqués
dans l'Introduction et/ou dans la liste des déclarations de brevets reçues par l'ISO
(voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données pour
information, par souci de commodité, à l'intention des utilisateurs et ne sauraient constituer un engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l'ISO liés à l'évaluation de la conformité, ou pour toute information au sujet de l'adhésion de
l'ISO aux principes de l'Organisation mondiale du commerce (OMC) concernant les obstacles techniques au
commerce (OTC), voir www.iso.org/avant-propos.
Le présent document a été élaboré par le comité technique ISO/TC 67, Industries du pétrole et du gaz, y
compris les énergies à faible teneur en carbone, Sous-comité SC 7, Structures en mer, en collaboration avec le
comité technique CEN/TC 12, Industries du pétrole et du gaz, y compris les énergies à faible teneur en carbone
du Comité européen de normalisation (CEN), conformément à l'Accord de coopération technique entre l'ISO
et le CEN (Accord de Vienne).
Cette quatrième édition annule et remplace la troisième édition (ISO 19901-2:2022), qui a fait l'objet d'une
révision technique.
Les principales modifications sont les suivantes :
— domaine d'application étendu pour couvrir les éoliennes en mer et les autres structures d'énergie
renouvelable en mer ;
— incorpore les exigences de spécifications courantes dans l'industrie (IOGP JIP 35) ;
— les cartes d'aléas sismiques ont été mises à jour ;
— rédaction avec des exigences claires et concises.
Une liste de toutes les parties de la série ISO 19901 se trouve sur le site web de l'ISO.
v
ISO/DIS 19901‐2:2024(fr)
Il convient que l'utilisateur adresse tout retour d'information ou toute question concernant le présent
document à l'organisme national de normalisation de son pays. Une liste exhaustive desdits organismes se
trouve à l'adresse www.iso.org/fr/members.html.
vi
ISO/DIS 19901‐2:2024(fr)
Introduction
Les Normes internationales des structures en mer élaborées par le TC 67 traitent des exigences et des
évaluations de la conception de toutes les structures en mer utilisées dans le monde entier par le secteur
énergétique. Leur application a pour finalité d'atteindre des niveaux de qualité et de sécurité appropriés
pour les structures en mer normalement occupées et normalement inoccupées, quel que soit le type de
structure et quelle que soit la nature ou la combinaison des matériaux utilisés.
L'intégrité structurelle est un concept global comprenant des modèles destinés à décrire des actions, des
analyses structurelles, des règles de conception ou d'évaluation, des éléments de sécurité, l'exécution des
réalisations, des procédures de contrôle de la qualité, et des exigences nationales, ces divers éléments étant
interdépendants. La modification d'un aspect de la conception ou de l'évaluation pris isolément peut
perturber l'équilibre de la fiabilité inhérent au concept global ou au système structurel global. Par
conséquent, il est nécessaire que les implications des modifications soient considérées par rapport à la
fiabilité globale de l'ensemble des systèmes de structures en mer.
Les Normes internationales pour les structures en mer préparées par le TC 67 sont élaborées pour
permettre un choix étendu de configurations structurelles, de matériaux, et de techniques sans entraver
l'innovation. Une solide capacité de jugement en termes d'ingénierie est donc nécessaire pour l'utilisation
de ces Normes internationales.
Le concept global d'intégrité structurelle est décrit ci-dessus. Certains facteurs supplémentaires doivent être
pris en compte pour la conception sismique. Ceux-ci comprennent la magnitude et la probabilité des
événements sismiques, l'utilisation et l'importance de la structure en mer, la robustesse de la structure
envisagée et les dommages admissibles causés par des actions sismiques ayant différentes probabilités
d'occurrence. Il est nécessaire que tout cela, ainsi que toute autre information applicable, soit considéré en
relation avec la fiabilité globale de la structure.
Les conditions sismiques varient fortement en fonction de la situation géographique et les critères de
conception dépendent principalement des observations d'événements sismiques historiques, ainsi que du
contexte sismotectonique et des conditions de sol locales. Dans bien des cas, des études d'évaluation de l'aléa
sismique spécifiques au site sont requises pour réaliser la conception ou l'évaluation d'une structure.
L'objectif du présent document est de fournir des procédures générales de conception sismique pour
différents types de structures en mer et un cadre pour la détermination des critères de conception sismique.
D'autres exigences sont énoncées dans les exigences générales de la Norme internationale ISO 19900 et dans
les Normes internationales spécifiques relatives aux structures ISO 19902, ISO 19903, ISO 19904, et
ISO 19906. La prise en compte des événements sismiques dans l'évaluation des unités mobiles en mer est
traitée dans l'ISO 19905.
vii
PROJET de Norme internationale ISO/DIS 19901‐2:2024(fr)

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
1 Domaine d'application
Le présent document contient des dispositions relatives à la conception et à l'évaluation sismiques des
structures en mer.
Des recommandations concernant les effets des événements sismiques sur les structures flottantes sont
présentées.
La conception et l'évaluation des mouvements du sol induits par les séismes sont spécifiquement traitées.
D'autres phénomènes dangereux géologiques tels que la liquéfaction, l'instabilité des pentes, les failles,
les tsunamis, les volcans de boue et les ondes de choc sont brièvement couverts.
Les dispositions s'appliquant à la réalisation d'une analyse probabiliste de l'aléa sismique, spécifique au
site, sont fournies pour les structures en mer installées dans des zones à forte activité sismique et pour
les structures en mer ayant des niveaux de conséquences élevés.
NOTE Des recommandations et des informations générales relatives aux exigences sont incluses à l'Annexe A.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu'ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l'édition citée s'applique.
Pour les références non datées, la dernière édition du document de référence s'applique (y compris les
éventuels amendements).
ISO 19900, Industries du pétrole et du gaz naturel — Exigences générales relatives aux structures en mer
3 Termes et définitions (En suspens)
Pour les besoins du présent document, les termes et les définitions de l'ISO 19900 ainsi que les suivants
s'appliquent.
L'ISO et l'IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes :
— ISO Online browsing platform : disponible à l'adresse https://www.iso.org/obp
— IEC Electropedia : disponible à l'adresse https://www.electropedia.org/
3.1
séisme de niveau anormal
ALE [abnormal level earthquake]
séisme intense de sévérité anormale avec une très faible probabilité d'occurrence au cours de la durée de
vie de la structure, généralement d'une période de retour de l'ordre du millier d'années
Note 1 à l'article : L'événement ALE est comparable aux événements anormaux dans la conception de structures
[6] [7]
fixes qui sont décrits dans l'ISO 19902 et l'ISO 19903 .
ISO/DIS 19901‐2:2024(fr)
3.2
atténuation
déclin des ondes sismiques au cours de leur propagation depuis leur source jusqu'au site considéré
3.3
désagrégation
séparation de la contribution aux aléas sismiques à partir de différentes zones de failles et de sources
sismiques
3.4
voies et systèmes d'évacuation
système installé sur une structure en mer pour faciliter l'évacuation en cas d'urgence
EXEMPLE Passages, goulottes, échelles, canots de sauvetage et héliponts.
3.5
séisme de niveau extrême
ELE [extreme level earthquake]
séisme de grande force ayant une probabilité d'occurrence raisonnable au cours de la durée de vie de la
structure, généralement d'une période de retour de l'ordre de la centaine d'années
3.6
mouvement de faille
mouvement se produisant au niveau d'une faille au cours d'un séisme
3.7
mouvement sismique du sol
accélérations, vitesses ou déplacements du sol générés par les ondes sismiques se propageant depuis
l'hypocentre des séismes
Note 1 à l'article : Les fondations d'une structure en mer fixe reposent dans ou sur le sous‐sol marin (3.17) ; par
conséquent, seuls les mouvements sismiques du sous-sol marin sont significatifs. L'expression « mouvements
sismiques du sol » est préférée à « mouvements sismiques du sous-sol marin » par souci de cohérence avec la
terminologie utilisée dans le domaine de la conception sismique pour les structures à terre.
Note 2 à l'article : Les mouvements sismiques du sol peuvent se produire à une profondeur spécifique ou sur une
zone spécifique du sous-sol marin.
3.8
liquéfaction
fluidisation d'un sol en raison de l'augmentation des pressions interstitielles générées par l'action du
séisme dans des conditions non drainées
3.9
combinaison modale
combinaison des valeurs de réponse associées à chaque mode dynamique d'une structure
3.10
volcan de boue
intrusion diapirique d'argile plastique provoquant des suintements d'eau et de gaz sous haute pression
qui font remonter de la boue, des fragments de roche (et occasionnellement du pétrole) à la surface
Note 1 à l'article : Un volcan de boue se présente sur le fond marin sous la forme d'un cône de boue duquel s'échappe
du gaz en continu ou de manière sporadique.
ISO/DIS 19901‐2:2024(fr)
3.11
analyse probabiliste de l'aléa sismique
PSHA [probabilistic seismic hazard analysis]
cadre d'étude permettant l'identification, la quantification et la combinaison rationnelle des incertitudes
relatives à l'intensité des séismes, leurs emplacements, leurs taux de récurrence et les variations dans les
caractéristiques des mouvements sismiques du sol (3.7)
3.12
probabilité de dépassement
probabilité qu'une variable (ou un événement) dépasse un niveau de référence spécifié pour un temps
d'exposition donné
EXEMPLE Les probabilités annuelles de dépassement d'une certaine magnitude d'accélération sismique du sol,
de vitesse du sol ou de déplacement du sol.
3.13
réponse spectrale
réponses maximales d'une série de systèmes à degré de liberté unique soumis à un mouvement de base
donné, tracées comme une fonction des fréquences naturelles pour des valeurs spécifiques
d'amortissement
3.14
système de sécurité
système installé sur une structure en mer, destiné à détecter, maîtriser et réduire le plus possible les
situations dangereuses
EXEMPLE Dispositifs de détection de gaz, d'arrêt d'urgence, de protection contre les incendies et leurs systèmes
de commande.
3.15
fond marin
interface entre la mer et le sous‐sol marin (3.17)
3.16
glissement du sous‐sol marin
effondrement des pentes du sous‐sol marin (3.17)
3.17
sous‐sol marin
matériaux du sol situés sous la mer dans lesquels reposent les fondations de la structure
3.18
catégorie de risque sismique
SRC [seismic risk category]
catégorie définie à partir du niveau de conséquences et de l'intensité des mouvements sismiques (c'est-
à-dire l'accélération spectrale ayant une probabilité annuelle de dépassement de 1/1 000)
3.19
courbe d'aléa sismique
courbe indiquant la probabilité de dépassement (3.12) annuelle en fonction d'une mesure de l'intensité
sismique
Note 1 à l'article : Les mesures d'intensité sismique peuvent comprendre des paramètres tels que l'accélération
maximale du sol, l'accélération spectrale (3.22) ou la vitesse spectrale (3.23).
ISO/DIS 19901‐2:2024(fr)
3.20
coefficient de réserve de capacité sismique
coefficient indiquant l'aptitude de la structure à supporter les mouvements du sol induits par des séismes
au-delà du niveau du séisme de niveau extrême (3.5)
Note 1 à l'article : Voir A.9.3.6 pour plus de détails.
3.21
analyse de la réponse du site
analyse de la propagation des ondes permettant d'évaluer l'effet des conditions géologiques locales et
des conditions de sol sur les mouvements sismiques du sol (3.7) au fur et à mesure que les ondes se
propagent du fond vers la surface au niveau du site
3.22
accélération spectrale
réponse maximale de l'accélération absolue d'un oscillateur à degré de liberté unique soumis à des
mouvements sismiques du sol (3.7)
3.23
vitesse spectrale
réponse maximale de la pseudo-vitesse d'un oscillateur à degré de liberté unique soumis à des
mouvements sismiques du sol (3.7)
Note 1 à l'article : Le spectre de pseudo-vitesse est calculé en factorisant les spectres de déplacement ou
d'accélération, respectivement par la fréquence angulaire de l'oscillateur ou l'inverse de sa fréquence.
3.24
déplacement spectral
réponse maximale du déplacement relatif d'un oscillateur à degré de liberté unique soumis à des
mouvements sismiques du sol (3.7)
3.25
analyse statique en poussée progressive
application et augmentation progressive d'un ensemble global d'actions statiques sur une structure, y
compris des actions inertielles dynamiques équivalentes, jusqu'à l'apparition d'un mécanisme global de
rupture
3.26
tsunami
vagues de mer de longue période dues à de rapides mouvements verticaux du fond marin (3.15)
Note 1 à l'article : Le mouvement vertical du fond marin est souvent associé à une rupture de faille pendant les
séismes ou à des glissements du sous‐sol marin (3.16).
4 Symboles et abréviations (En suspens)
4.1 Symboles
a
pente de queue de la courbe d'aléa sismique
R
C coefficient de site, un facteur de correction appliqué à la partie accélération (périodes
a
plus courtes) d'une réponse spectrale
ISO/DIS 19901‐2:2024(fr)
C facteur de correction appliqué à l'accélération spectrale pour tenir compte des
c
incertitudes non prises en compte dans une courbe d'aléa sismique
C coefficient de réserve de capacité sismique ; voir Formules (7) et (10)
r
C coefficient de site, un facteur de correction appliqué à la partie vitesse (périodes plus
v
longues) d'une réponse spectrale
D facteur d'échelle pour l'amortissement
G module de cisaillement initial (faible déformation) du sol
max
g accélération due à la pesanteur
M magnitude d'un séisme mesurée par l'énergie libérée à sa source
N facteur d'échelle pour convertir le spectre d'accélération du site sur une période de
ALE
retour de 1 000 ans en spectre d'accélération ALE du site
p pression atmosphérique
a
P probabilité annuelle de dépassement pour l'événement ALE
ALE
P probabilité de dépassement
e
P probabilité annuelle de dépassement pour l'événement ELE
ELE
P objectif de probabilité annuelle de défaillance
f
q résistance à la pénétration au cône du sol
c
q résistance normalisée à la pénétration au cône du sol
cl
qc""l
résistance normalisée moyenne à la pénétration au cône du sable dans le sous-sol
marin effectif
ST accélération spectrale associée à une période d'oscillateur à degré de liberté
a
unique, T
T accélération spectrale moyenne associée à une période d'oscillateur à degré de
liberté unique, T ; obtenue à partir d'une étude PSHA
ST  est l'accélération spectrale pour une période d'oscillateur à degré de liberté unique
aA, LE
T résultant d'une suite d'accélérogrammes qui, lorsque la structure y est exposée,
se traduit par une probabilité d'effondrement de 50 %
ST accélération spectrale ELE associée à une période d'oscillateur à degré de liberté
 
aE, LE
unique, T
ST  accélération spectrale au rocher pour une période de retour de 1 000 ans, obtenue à
am, ap
partir des cartes associées à une période d'oscillateur à degré de liberté unique, T
ST
  accélération spectrale moyenne associée à une probabilité de dépassement, P , et à
e
aP,
e
une période d'oscillateur à degré de liberté unique, T, obtenue à partir d'une étude
PSHA
ST 
accélération spectrale ayant une probabilité annuelle associée à une probabilité
aP,
NC
annuelle cible de défaillance, P , et à une période d'oscillateur à degré de liberté
f
unique, T, obtenue à partir d'une étude PSHA
ST  accélération spectrale du site correspondant à une période de retour de 1 000 ans et
as,ite
à une période d'oscillateur à degré de liberté unique, T
s résistance au cisaillement sans drainage du sol
u
ISO/DIS 19901‐2:2024(fr)
s̅résistance moyenne au cisaillement sans drainage du sol dans le sous-sol marin
u
effectif
T période naturelle d'un oscillateur simple à degré de liberté unique
T période modale dominante de la structure
dom
T période de retour
return
v vitesse représentative de propagation de l'onde de cisaillement
s
vitesse représentative moyenne de propagation de l'onde de cisaillement dans le sous-
sol marin effectif
ρ masse volumique du sol
η pourcentage d'amortissement critique
σ écart-type logarithmique des incertitudes non prises en compte dans une courbe
LR
d'aléa sismique
σ′ contrainte effective verticale du sol in situ
v0
4.2 Abréviations
DL état limite de limitation des dommages
DSHA analyse déterministe de l'aléa sismique
DSRA analyse dynamique de la réponse du site
L1, L2, L3 niveau de conséquences déterminé de l'ISO 19900
MOU unité mobile en mer
NC état limite de quasi-effondrement
NP poussée progressive non linéaire
NTHA analyse non linéaire faisant appel aux fonctions temporelles
PGA accélération maximale du sol
RP période de retour
THA analyse faisant appel aux fonctions temporelles
TLP plate-forme à ancrage tendu
ULS état limite ultime
5 Aléas sismiques
5.1 La conception et l'évaluation sismiques des structures en mer doivent inclure l'effet des
mouvements du sol dus aux séismes.
5.2 La conception et l'évaluation des structures en mer doivent également inclure les effets des
événements dangereux sismiques suivants, tels qu'établis par les spécialistes des phénomènes dangereux
des sites géologiques :
a) liquéfaction du sol ;
b) glissement du sous-sol marin ;
ISO/DIS 19901‐2:2024(fr)
c) mouvement de faille ;
d) tsunamis ;
e) volcans de boue ;
f) impulsion de vitesse due aux effets de directivité.
6 Objectifs de performance, états limites et états d'endommagement
6.1 Généralités
6.1.1 Il doit être démontré que les risques dus à l'exposition de la structure à des événements
sismiques dangereux sont tolérables conformément aux 6.1.2 à 6.1.5.
NOTE Les exigences de l'ISO 19901-2 permettent à la structure d'avoir une résistance et une ductilité suffisantes
pour que les risques (sécurité des personnes, pollution de l'environnement, et perturbation de l'activité) soient
tolérables lorsque la structure est exposée à des événements dangereux sismiques tels que définis par la courbe
d'aléa pour le site.
6.1.2 La structure doit répondre aux objectifs de performance (tels que définis en 6.3).
6.1.3 La démonstration du fait que la structure répond aux objectifs de performance doit se faire par
une vérification aux états limites conformément à l'ISO 19900.
6.1.4 L'objectif de performance pour le risque de sécurité des personnes, généralement associé à l'ALE,
doit spécifier la probabilité annuelle maximale tolérable que l'état (d'endommagement) de la structure
puisse dépasser l'état limite de quasi-effondrement (NC).
NOTE 1 L'état limite NC est décrit en 6.2.1. Lorsque l'état de la structure est à l'état limite NC, le système structurel
reste stable, mais un ou plusieurs composants peuvent être défaillants. Puisque la structure demeure stable et ne
s'effondre pas, les décès sont limités ou évités à la suite de l'événement sismique, et ainsi, les conséquences pour la
vie et la sécurité des personnes sont négligeables.
6.1.5 L'objectif de performance pour le risque de perturbation de l'activité, généralement associé à
l'ELE, doit spécifier la probabilité annuelle maximale tolérable que l'état (d'endommagement) de la
structure puisse dépasser l'état limite de limitation des dommages (DL).
NOTE 1 L'état limite DL est décrit en 6.2.2. Lorsque l'état de la structure est à l'état limite DL, le système structurel
reste stable, mais le système latéral de la structure (entretoises, joints, et pieux) peut subir des déformations
approchant la limite d'élasticité. Tout dommage est localisé et facilement réparable, ce qui fait que la fonctionnalité
de l'installation est restaurée dans un court délai après l'événement sismique et que les conséquences d'une
perturbation de l'activité sont tolérables.
Une vérification aux états limites pour les états limites DL et NC doit être conforme aux Articles 6 à 10,
comme représenté à la Figure 1.
ISO/DIS 19901‐2:2024(fr)
ISO/DIS 19901‐2:2024(fr)
Anglais Français
determine S (1,0) déterminer S (1,0)
a,map a,map
use maps in Annex B utiliser les cartes de l’Annexe B
déterminer le niveau de conséquences pour
determine the consequence level for the facility l’installation
determine the site seismic zone déterminer la zone sismique du site
determine the seismic risk category, SRC, for the déterminer la catégorie de risque sismique, SRC, pour
facility l’installation
no limit state verification for SRC 1 pas de vérification aux états limites pour la SRC 1
a a
for SRC 2 and SRC 3 , determine S (T) and pour les SRC 2 et SRC 3 , déterminer S (T) et
a,ELE a,ELE
S (T) from clause 8 S (T) à partir de l’Article 8
a,ALE a,ALE
a a
for SRC 3 and SRC 4, determine S (T) and pour les SRC 3 et SRC 4, déterminer S (T)
a,ELE a,ELE
S (T) from clause 9 et S (T) à partir de l’Article 9
a,ALE a,ALE
perform site specific PSHA réaliser une PSHA spécifique au site
site specific DHSA in optional (DHSA spécifique au site en option)
determine S (T) déterminer S (T)
a,site a,site
réaliser une DSRA spécifique au site pour les sites
perform site specific DSRA for sites with soft to very ayant un sol mou à très rigide au-dessus du substratum
stiff soil above bedrock rocheux
determine tail slope of hazard curve at the S (T) with déterminer la pente de queue de la courbe d’aléa à
a
exceedance prob. P la S (T) avec une prob. de dépassement P
NC a NC
determine S (T) and S (T) déterminer S (T) et S (T )
a,ALE a,ALE dom a,ALE a,ALE dom
determine the correction factor C déterminer le facteur de correction C
c c
determine S (T) déterminer S (T )
a,ALE dom a,ALE dom
déterminer le coefficient de réserve de capacité
determine seismic reserve capacity factor C sismique C
r r
déterminer le coefficient de réserve de capacité
determine seismic reserve capacity factor C sismique C
r r
determine S (T) and S (T) déterminer S (T) et S (T )
a,ELE a,ELE dom a,ELE a,ELE dom
perform structural response analysis (RSA, THA, SPA, réaliser une analyse de la réponse structurelle (RSA,
depending on SRC) for limit state verification of NC and THA, SPA, en fonction de la SRC) pour une vérification
DL limit states aux états limites des états limites NC et DL
Figure 1 — Étapes d'une vérification aux états limites
NOTE Une vérification aux états limites d'installations SRC 3 peut s'effectuer à partir de l'Article 8 ou de
l'Article 9.
6.2 États limites et états d'endommagement
6.2.1 Pour ce qui est de l'état de la structure à l'état limite de quasi-effondrement (NC) associé à l'ALE :
a) il ne doit pas inclure un effondrement du système gravitaire de la structure (c'est-à-dire les jambes,
la capacité axiale du sol et la connexion entre les pieux et les jambes) ou un effondrement du
sous-système qui soutient les quartiers vie ;
b) il peut inclure des dommages aux éléments (par exemple, des déformations plastiques, un
flambement local plastique dans l'acier ou un écaillage dans le béton) ;
c) il peut inclure des entretoises sectionnées (par rupture ou fatigue à faible cycle) ;
d) il peut inclure une plasticité au niveau des joints ;
ISO/DIS 19901‐2:2024(fr)
e) il peut inclure un effondrement ou une rupture des joints ;
f) il peut inclure une contrainte de traction plastique inférieure à la contrainte de rupture dans les
pieux ;
NOTE La DNV-RP-C208 fournit des recommandations sur les limites de rupture pour une déformation locale.
g) il ne doit pas inclure des dommages aux systèmes de sécurité, aux sorties de secours, et aux systèmes
d'évacuation qui empêchent leur fonctionnalité ;
h) il ne doit pas inclure une perte de supports pour un équipement critique pour les hydrocarbures qui
pourrait conduire à une escalade par perte de confinement du processus (LOPC) ;
i) il ne doit pas inclure un effondrement des quartiers vie, des mâts, des derricks, des structures de
torche et des autres structures critiques pour la sécurité.
6.2.2 Pour ce qui est de l'état de la structure à l'état limite de limitation des dommages (DL) associé à
l'ELE :
a) il ne doit pas inclure des dommages aux composants du système gravitaire de la structure
(c'est-à-dire les jambes, la capacité axiale du sol et la connexion entre les pieux et les jambes) ;
b) il ne doit pas inclure des dommages dus à des mécanismes de fragilisation (par exemple, flambement
de flexion, flambement local dans l'acier ou écaillage dans le béton) ;
NOTE L'ISO 19902 exige que l'action sismique soit augmentée d'un facteur de C pour des vérifications de code
r
des éléments de jambe lorsque la structure est soumise à des actions sismiques d'intensité S .
aE, LE
c) il convient qu'il limite les déformations au niveau de la fibre extérieure des entretoises, des joints et
des pieux (c'est-à-dire la contrainte de flexion plus la déformation axiale) à la limite d'élasticité ;
NOTE L'ISO 19902 exige que le système latéral (entretoises, joints, et pieux) soit dimensionné pour la ductilité
et puisse ainsi se déformer plastiquement sans flambement local lors d'actions sismiques d'intensité S .
aA, LE
d) il ne doit pas inclure des dommages aux systèmes de sécurité, aux sorties de secours, et aux systèmes
d'évacuation qui empêchent leur fonctionnalité ;
e) il ne doit pas inclure des dommages aux conduites, aux tubes conducteurs, aux prolongateurs et aux
autres composants critiques pour la sécurité dus à des déplacements au niveau de l'élévation de la
ligne de boue de la structure ;
f) il ne doit pas inclure des dommages dus à un basculement des équipements de la superstructure et
des chemins de câbles ;
g) il ne doit pas inclure des dommages aux mâts, aux derricks, et aux structures de torche ;
h) il ne doit pas inclure des dommages aux supports glissants qui empêchent leur fonctionnalité ;
i) il ne doit pas inclure des dommages aux systèmes de tuyauterie qui empêchent leur fonctionnalité
du fait d'un déplacement différentiel de supports ;
j) il convient qu'il n'inclue pas de dommages qui se traduisent par des chutes d'objets.
ISO/DIS 19901‐2:2024(fr)
6.3 Objectifs de performance
6.3.1 La vérification à l'état limite NC de la structure doit être démontrée pour l'événement ALE
conformément à 6.3.2.
6.3.2 La probabilité annuelle que la structure dépasse l'état limite NC, tel que défini en 6.2.1, ne doit
P
pas être supérieure à la valeur de indiquée dans le Tableau 1.
NC
Tableau 1 — Probabilité annuelle maximale de dépassement de l'état limite NC
Niveau de
P
NC
conséquences
−4
L1
4 × 10 = 1/2 500
−3
L2
1 × 10 = 1/1 000
−3
L3
2,5 × 10 = 1/400
NOTE 1 La probabilité annuelle dans le Tableau 1 pour le NC tient compte de l'incertitude épistémique dans la
probabilité annuelle et est déterminée par l'utilisation de la courbe d'aléa moyenne et de la courbe de fragilité
moyenne.
NOTE 2 La procédure simplifiée de l'Article 8 a été étalonnée en fonction des probabilités énumérées dans le
Tableau 1.
6.3.3 La probabilité maximale annuelle de dépassement de l'état limite NC peut être inférieure à celle
indiquée dans le Tableau 1 si cela est spécifié par l'opérateur ou le régulateur.
6.3.4 La vérification à l'état limite DL de la structure doit être démontrée conformément aux
événements ELE définis en 6.3.5.
6.3.5 La probabilité annuelle que la structure telle que conçue dépasse l'état limite DL, tel que défini
en 6.2.2, ne doit pas être supérieure à P ou à la valeur de P indiquée dans le Tableau 2
ELE DL
Tableau 2 — Probabilité annuelle maximale de dépassement de l'état limite DL
Niveau de conséquences P
DL
1 / 200
L1
1 / 100
L2
1/50
L3
où P est définie à la Figure 7.
ELE
6.4 Catégorie de risque sismique
6.4.1 L'installation doit être classée par catégorie de risque sismique (SRC) conformément au
Tableau 3.
NOTE La SRC est fonction du niveau de conséquences et de la zone sismique du site.
ISO/DIS 19901‐2:2024(fr)
6.4.2 La zone sismique du site doit être déterminée à partir des cartes d'accélération spectrale
horizontale pour 1,0 s de l'Annexe B ou d'une étude d'aléa sismique spécifique au site.
Tableau 3 — Catégorie de risque sismique (SRC)
Niveau de conséquences
S 1,0
a ,map Zone sismique
(voir l'ISO 19900: 2019, 7.3)
du site
(voir Annexe B)
L1 L2 L3
< 0,03 g 0 SRC 1 SRC 1 SRC 1
0,03 g à 0,10 g 1 SRC 3 SRC 2 SRC 2
0,11 g à 0,25 g 2 SRC 4 SRC 2 SRC 2
0,26 g à 0,45 g 3 SRC 4 SRC 3 SRC 2
> 0,45 g 4 SRC 4 SRC 4 SRC 3
6.4.3 Pour les situations de conception sismique, une structure ne doit pas être classée au niveau de
conséquences L2 à moins qu'elle ne soit normalement inoccupée (sauf pendant de brèves périodes telles
que pour le contrôle et la maintenance), mais avec un niveau de conséquences pour la pollution
d'environnement supérieur à L3.
NOTE Il est pris pour hypothèse qu'aucune prévision fiable des actions sismiques n'est réalisable et, par
conséquent, qu'il n'est pas possible d'évacuer avant un séisme.
6.5 Vérification à l'état limite DL (utilisation d'événements dangereux ayant une
intensité = S )
aE, LE
6.5.1 La S doit être déterminée conformément à l'Article 8 ou à l'Article 9, en fonction de la SRC
aE, LE
(comme décrit en 6.8).
6.5.2 Une vérification à l'état limite DL doit être effectuée en utilisant :
a) des actions découlant d'historiques dans le temps de mouvements du sol où chaque mouvement du
sol a une accélération spectrale, à la période d'oscillation de la structure, définie par S ;
aE, LE
b) des capacités représentatives des éléments, des joints, des pieux, et du sol, telles que définies dans
l'ISO 19900.
NOTE L'Article 7 fournit des types d'analyse et des exigences pour déterminer les actions ci-dessus.
6.5.3 Une vérification à l'état limite DL de la structure doit être considérée comme ayant été démontrée
à condition que les formules 11.5-1 et 11.5-2 de l'ISO 19902:2020 soient satisfaites.
6.6 Vérification à l'état limite NC (utilisation d'événements dangereux ayant une
intensité = S )
aA, LE
6.5.1 La S doit être déterminée conformément à l'Article 8 ou à l'Article 9, en fonction de la SRC
aA, LE
(comme décrit en 6.8).
ISO/DIS 19901‐2:2024(fr)
6.6.1 Une vérification à l'état limite NC doit être effectuée en utilisant :
a) des actions découlant d'historiques dans le temps de mouvements du sol où chaque mouvement du
sol a une accélération spectrale, à la période d'oscillation de la structure, définie par S
...