SIST EN ISO 19901-2:2018

Petroleum and natural gas industries - Specific requirements for offshore structures - Part 2: Seismic design procedures and criteria (ISO 19901-2:2017)

ISO 19901-2:2017 contains requirements for defining the seismic design procedures and criteria for offshore structures; guidance on the requirements is included in Annex A. The requirements focus on fixed steel offshore structures and fixed concrete offshore structures. The effects of seismic events on floating structures and partially buoyant structures are briefly discussed. The site-specific assessment of jack-ups in elevated condition is only covered in ISO 19901-2:2017 to the extent that the requirements are applicable.
Only earthquake-induced ground motions are addressed in detail. Other geologically induced hazards such as liquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves are mentioned and briefly discussed.
The requirements are intended to reduce risks to persons, the environment, and assets to the lowest levels that are reasonably practicable. This intent is achieved by using:
a)   seismic design procedures which are dependent on the exposure level of the offshore structure and the expected intensity of seismic events;
b)   a two-level seismic design check in which the structure is designed to the ultimate limit state (ULS) for strength and stiffness and then checked to abnormal environmental events or the abnormal limit state (ALS) to ensure that it meets reserve strength and energy dissipation requirements.
Procedures and requirements for a site-specific probabilistic seismic hazard analysis (PSHA) are addressed for offshore structures in high seismic areas and/or with high exposure levels. However, a thorough explanation of PSHA procedures is not included.
Where a simplified design approach is allowed, worldwide offshore maps, which are included in Annex B, show the intensity of ground shaking corresponding to a return period of 1 000 years. In such cases, these maps may be used with corresponding scale factors to determine appropriate seismic actions for the design of a structure.
For design of fixed steel offshore structures, further specific requirements and recommended values of design parameters (e.g. partial action and resistance factors) are included in ISO 19902, while those for fixed concrete offshore structures are contained in ISO 19903. Seismic requirements for floating structures are contained in ISO 19904, for site-specific assessment of jack-ups and other MOUs in ISO 19905 (all parts), for arctic structures in ISO 19906 and for topsides structures in ISO 19901‑3.

Erdöl- und Erdgasindustrie - Spezielle Anforderungen für Offshore-Anlagen - Teil 2: Seismische Auslegungsverfahren und –kriterien (ISO 19901-2:2017)

Industries du pétrole et du gaz naturel - Exigences spécifiques relatives aux structures en mer - Partie 2: Procédures de conception et critères sismiques (ISO 19901-2:2017)

ISO 19901-2:2017 spécifie les exigences relatives à la définition des procédures et critères de conception parasismique pour les structures en mer; les préconisations concernant les exigences sont indiquées dans l'Annexe A. Les exigences portent sur les structures en mer fixes en acier et en béton. Les effets d'événements sismiques sur les structures flottantes et partiellement flottantes sont brièvement décrits. L'évaluation, spécifique au site, des plates-formes auto-élévatrices en situation surélevée est uniquement traitée dans le présent document dans la mesure où les exigences sont applicables.
Seuls les mouvements du sol induits par des séismes sont traités en détail. D'autres risques géologiques tels que la liquéfaction, l'instabilité des pentes, les failles, les tsunamis, les volcans de boue et les ondes de choc sont également mentionnés et brièvement décrits.
Les exigences sont destinées à réduire les risques encourus par les personnes, l'environnement et les installations au niveau de risque le plus bas qui soit raisonnablement réalisable. Cette intention est atteinte à l'aide:
a)    de procédures de conception parasismique qui dépendent du niveau d'exposition de la structure en mer et de l'intensité prévue des événements sismiques;
b)    d'un contrôle de conception parasismique à deux niveaux, dans lequel la structure est conçue selon l'état limite ultime (ULS) en termes de résistance et de rigidité avant d'être confrontée à des événements environnementaux anormaux ou à l'état limite anormal (ALS), afin de garantir qu'elle satisfait aux exigences de résistance de réserve et de dissipation d'énergie.
Les procédures et exigences s'appliquant à la réalisation d'une analyse probabiliste de l'aléa sismique (PSHA), spécifique au site, sont exposées pour les structures en mer installées dans des zones à forte activité sismique et/ou fortement exposées. Cependant, ces procédures de l'étude PSHA ne sont pas expliquées de manière approfondie.
Lorsqu'une approche de conception simplifiée est admise, des cartes internationales, incluses dans l'Annexe B, indiquent l'intensité des secousses en mer pour une période de retour de 1 000 ans. Dans de tels cas, ces cartes peuvent être utilisées avec des facteurs d'échelle correspondants afin de déterminer les actions sismiques appropriées pour la conception d'une structure.
Pour la conception des structures en mer fixes en acier, d'autres exigences spécifiques et des valeurs recommandées des paramètres de conception (par exemple facteurs d'action partiels et de résistance) sont indiquées dans l'ISO 19902, tandis que celles relatives aux structures en mer fixes en béton sont énoncées dans l'ISO 19903. L'ISO 19904 intègre des exigences parasismiques relatives aux structures flottantes, l'ISO 19905 (toutes les parties) des exigences relatives à l'évaluation spécifique au site de plates-formes auto-élévatrices et autres MOU, l'ISO 19906 des exigences relatives aux structures arctiques et l'ISO 19901‑3 des exigences relatives aux superstructures.

Industrija za predelavo nafte in zemeljskega plina - Posebne zahteve za naftne ploščadi - 2. del: Postopki potresno varnega projektiranja in potresna merila (ISO 19901-2:2017)

General Information

• Status: Withdrawn
• Public Enquiry End Date: 29-Oct-2015
• Publication Date: 10-Jan-2018
• Withdrawal Date: 13-Jul-2022
• ICS: 75.180.10 - Exploratory, drilling and extraction equipment
• ICS: 91.120.25 - Seismic and vibration protection
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 14-Jul-2022
• Due Date: 06-Aug-2022
• Completion Date: 14-Jul-2022
• Ref Project: EN ISO 19901-2:2017 - Petroleum and natural gas industries - Specific requirements for offshore structures - Part 2: Seismic design procedures and criteria (ISO 19901-2:2017)

Relations

• Replaced By: SIST EN ISO 19901-2:2022 - Petroleum and natural gas industries - Specific requirements for offshore structures - Part 2: Seismic design procedures and criteria (ISO 19901-2:2022)
• Effective Date: 13-Jul-2022
• Revised: SIST EN ISO 19901-2:2005 - Petroleum and natural gas industries - Specific requirements for offshore structures - Part 2: Seismic design procedures and criteria (ISO 19901-2:2004)
• Effective Date: 01-Oct-2015
• Replaces: SIST EN ISO 19901-2:2005 - Petroleum and natural gas industries - Specific requirements for offshore structures - Part 2: Seismic design procedures and criteria (ISO 19901-2:2004)
• Effective Date: 20-Dec-2017
• Replaces: SIST EN ISO 19901-2:2005 - Petroleum and natural gas industries - Specific requirements for offshore structures - Part 2: Seismic design procedures and criteria (ISO 19901-2:2004)
• Effective Date: 08-Jun-2022

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 19901-2:2018
01-marec-2018
1DGRPHãþD
SIST EN ISO 19901-2:2005
,QGXVWULMD]DSUHGHODYRQDIWHLQ]HPHOMVNHJDSOLQD3RVHEQH]DKWHYH]DQDIWQH
SORãþDGLGHO3RVWRSNLSRWUHVQRYDUQHJDSURMHNWLUDQMDLQSRWUHVQDPHULOD,62

Petroleum and natural gas industries - Specific requirements for offshore structures -
Part 2: Seismic design procedures and criteria (ISO 19901-2:2017)
Erdöl- und Erdgasindustrie - Spezielle Anforderungen für Offshore-Anlagen - Teil 2:
Seismische Auslegungsverfahren und –kriterien (ISO 19901-2:2017)
Industries du pétrole et du gaz naturel - Exigences spécifiques relatives aux structures
en mer - Partie 2: Procédures de conception et critères sismiques (ISO 19901-2:2017)
Ta slovenski standard je istoveten z: EN ISO 19901-2:2017
ICS:
75.180.10 Oprema za raziskovanje, Exploratory, drilling and
vrtanje in odkopavanje extraction equipment
91.120.25 =DãþLWDSUHGSRWUHVLLQ Seismic and vibration
YLEUDFLMDPL protection
SIST EN ISO 19901-2:2018 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 19901-2:2018

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SIST EN ISO 19901-2:2018


EN ISO 19901-2
EUROPEAN STANDARD

NORME EUROPÉENNE

December 2017
EUROPÄISCHE NORM
ICS 75.180.10 Supersedes EN ISO 19901-2:2004
English Version

Petroleum and natural gas industries - Specific
requirements for offshore structures - Part 2: Seismic
design procedures and criteria (ISO 19901-2:2017)
Industries du pétrole et du gaz naturel - Exigences Erdöl- und Erdgasindustrie - Spezielle Anforderungen
spécifiques relatives aux structures en mer - Partie 2: für Offshore-Anlagen - Teil 2: Seismische
Procédures de conception et critères sismiques (ISO Auslegungsverfahren und -kriterien (ISO 19901-
19901-2:2017) 2:2017)
This European Standard was approved by CEN on 18 November 2017.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19901-2:2017 E
worldwide for CEN national Members.

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SIST EN ISO 19901-2:2018
EN ISO 19901-2:2017 (E)
Contents Page
European foreword . 3

2

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SIST EN ISO 19901-2:2018
EN ISO 19901-2:2017 (E)
European foreword
This document (EN ISO 19901-2:2017) has been prepared by Technical Committee ISO/TC 67
"Materials, equipment and offshore structures for petroleum, petrochemical and natural gas industries"
in collaboration with Technical Committee CEN/TC 12 “Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries” the secretariat of which is held by CYS.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2018, and conflicting national standards shall be
withdrawn at the latest by June 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 19901-2:2004.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 19901-2:2017 has been approved by CEN as EN ISO 19901-2:2017 without any
modification.

3

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SIST EN ISO 19901-2:2018

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SIST EN ISO 19901-2:2018
INTERNATIONAL ISO
STANDARD 19901-2
Second edition
2017-11
Petroleum and natural gas
industries — Specific requirements
for offshore structures —
Part 2:
Seismic design procedures and
criteria
Industries du pétrole et du gaz naturel — Exigences spécifiques
relatives aux structures en mer —
Partie 2: Procédures de conception et critères sismiques
Reference number
ISO 19901-2:2017(E)
©
ISO 2017

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SIST EN ISO 19901-2:2018
ISO 19901-2:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2017 – All rights reserved

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SIST EN ISO 19901-2:2018
ISO 19901-2:2017(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3  Terms and definitions . 2
4 Symbols and abbreviated terms . 5
4.1 Symbols . 5
4.2 Abbreviated terms . 6
5  Earthquake hazards . 7
6 Seismic design principles and methodology . 7
6.1 Design principles . 7
6.2 Seismic design procedures . 8
6.2.1 General. 8
6.2.2 Extreme level earthquake design . 9
6.2.3 Abnormal level earthquake design .10
6.3 Spectral acceleration data .11
6.4 Seismic risk category .11
6.5 Seismic design requirements.12
6.6 Site investigation .13
7  Simplified seismic action procedure .13
7.1 Soil classification and spectral shape .13
7.2 Seismic action procedure .17
8 Detailed seismic action procedure .18
8.1 Site-specific seismic hazard assessment .18
8.2 Probabilistic seismic hazard analysis .18
8.3 Deterministic seismic hazard analysis .19
8.4 Seismic action procedure .21
8.5 Local site response analyses .24
9  Performance requirements .24
9.1 ELE performance.24
9.2 ALE performance .25
Annex A (informative) Additional information and guidance .26
Annex B (informative) Simplified action procedure spectral accelerations .35
Annex C (informative) Regional information .46
Bibliography .50
© ISO 2017 – All rights reserved iii

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SIST EN ISO 19901-2:2018
ISO 19901-2:2017(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 documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore
structures for petroleum, petrochemical and natural gas industries, Subcommittee SC 7, Offshore
structures.
This second edition cancels and replaces the first edition (ISO 19901-2:2004), which has been technically
revised.
A list of all parts in the ISO 19901 series can be found on the ISO website.
iv © ISO 2017 – All rights reserved

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SIST EN ISO 19901-2:2018
ISO 19901-2:2017(E)

Introduction
The series of International Standards applicable to types of offshore structure, ISO 19900 to ISO 19906,
addresses design requirements and assessments of all offshore structures used by the petroleum and
natural gas industries worldwide. Through their application, the intention is to achieve reliability levels
appropriate for manned and unmanned offshore structures, whatever the type of structure and the
nature or combination of the materials used.
It is important to recognize that structural integrity is an overall concept comprising models for
describing actions, structural analyses, design or assessment rules, safety elements, workmanship,
quality control procedures and national requirements, all of which are mutually dependent. The
modification of one aspect of design or assessment in isolation can disturb the balance of reliability
inherent in the overall concept or structural system. The implications involved in modifications,
therefore, need to be considered in relation to the overall reliability of all offshore structural systems.
The series of International Standards applicable to the various types of offshore structure is intended
to provide a wide latitude in the choice of structural configurations, materials and techniques without
hindering innovation. Sound engineering judgement is, therefore, necessary in the use of these
International Standards.
The overall concept of structural integrity is described above. Some additional considerations apply for
seismic design. These include the magnitude and probability of seismic events, the use and importance
of the offshore structure, the robustness of the structure under consideration and the allowable damage
due to seismic actions with different probabilities. All of these, and any other relevant information,
need to be considered in relation to the overall reliability of the structure.
Seismic conditions vary widely around the world, and the design criteria depend primarily on
observations of historical seismic events together with consideration of seismotectonics. In many
cases, site-specific seismic hazard assessments will be required to complete the design or assessment
of a structure.
This document is intended to provide general seismic design procedures for different types of offshore
structures, and a framework for the derivation of seismic design criteria. Further requirements are
contained within the general requirements standard, ISO 19900, and within the structure-specific
standards, ISO 19902, ISO 19903, ISO 19904 and ISO 19906. The consideration of seismic events in
connection with mobile offshore units is addressed in ISO 19905.
Some background to and guidance on the use of this document is provided in Annex A. The clause
numbering in Annex A is the same as in the normative text to facilitate cross-referencing.
Regional information on expected seismic accelerations for offshore areas is provided in Annex B.
© ISO 2017 – All rights reserved v

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SIST EN ISO 19901-2:2018

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SIST EN ISO 19901-2:2018
INTERNATIONAL STANDARD ISO 19901-2:2017(E)
Petroleum and natural gas industries — Specific
requirements for offshore structures —
Part 2:
Seismic design procedures and criteria
1 Scope
This document contains requirements for defining the seismic design procedures and criteria for
offshore structures; guidance on the requirements is included in Annex A. The requirements focus on
fixed steel offshore structures and fixed concrete offshore structures. The effects of seismic events on
floating structures and partially buoyant structures are briefly discussed. The site-specific assessment
of jack-ups in elevated condition is only covered in this document to the extent that the requirements
are applicable.
Only earthquake-induced ground motions are addressed in detail. Other geologically induced hazards
such as liquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves are mentioned
and briefly discussed.
The requirements are intended to reduce risks to persons, the environment, and assets to the lowest
levels that are reasonably practicable. This intent is achieved by using:
a) seismic design procedures which are dependent on the exposure level of the offshore structure and
the expected intensity of seismic events;
b) a two-level seismic design check in which the structure is designed to the ultimate limit state (ULS)
for strength and stiffness and then checked to abnormal environmental events or the abnormal
limit state (ALS) to ensure that it meets reserve strength and energy dissipation requirements.
Procedures and requirements for a site-specific probabilistic seismic hazard analysis (PSHA) are
addressed for offshore structures in high seismic areas and/or with high exposure levels. However, a
thorough explanation of PSHA procedures is not included.
Where a simplified design approach is allowed, worldwide offshore maps, which are included in
Annex B, show the intensity of ground shaking corresponding to a return period of 1 000 years. In
such cases, these maps may be used with corresponding scale factors to determine appropriate seismic
actions for the design of a structure.
For design of fixed steel offshore structures, further specific requirements and recommended values
of design parameters (e.g. partial action and resistance factors) are included in ISO 19902, while those
for fixed concrete offshore structures are contained in ISO 19903. Seismic requirements for floating
structures are contained in ISO 19904, for site-specific assessment of jack-ups and other MOUs in
ISO 19905 (all parts), for arctic structures in ISO 19906 and for topsides structures in ISO 19901-3.
2 Normative references
The following documents are referred to in the text in such a way that some or all of 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, Petroleum and natural gas industries — General requirements for offshore structures
ISO 19901-8, Petroleum and natural gas industries — Specific requirements for offshore structures –
Part 8: Marine soils Investigation
© ISO 2017 – All rights reserved 1

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SIST EN ISO 19901-2:2018
ISO 19901-2:2017(E)

ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
ISO 19903, Petroleum and natural gas industries — Fixed concrete offshore structures
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 terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
abnormal level earthquake
ALE
intense earthquake of abnormal severity with a very low probability of occurring during the life of the
structure
Note 1 to entry: The ALE event is comparable to the abnormal event in the design of fixed structures which are
described in ISO 19902 and ISO 19903.
3.2
attenuation
decay of seismic waves as they travel from the earthquake source to the site under consideration
3.3
directional combination
combination of response values due to each of the three orthogonal components of earthquake-induced
ground motions
3.4
escape and evacuation system
system provided on the offshore structure to facilitate escape and evacuation in an emergency
EXAMPLE Passageways, chutes, ladders, life rafts and helidecks.
3.5
extreme level earthquake
ELE
strong earthquake with a reasonable probability of occurring during the life of the structure
Note 1 to entry: The ELE event is comparable to the extreme environmental event in the design of fixed structures
which are described in ISO 19902 and ISO 19903.
3.6
fault movement
movement occurring on a fault during an earthquake
3.7
ground motion
accelerations, velocities or displacements of the ground produced by seismic waves radiating away
from earthquake sources
Note 1 to entry: A fixed offshore structure is founded in or on the seabed (3.17) and consequently only seabed
motions are of significance. The term 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.
2 © ISO 2017 – All rights reserved

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SIST EN ISO 19901-2:2018
ISO 19901-2:2017(E)

3.8
liquefaction
fluidity of soil due to the increase in pore pressures caused by earthquake action under undrained
conditions
3.9
modal combination
combination of response values associated with each dynamic mode of a structure
3.10
mud volcano
diapiric intrusion of plastic clay causing high pressure gas-water seepages which carry mud, fragments
of rock (and occasionally oil) to the surface
Note 1 to entry: The surface expression of a mud volcano is a cone of mud with continuous or intermittent gas
escaping through the mud.
3.11
probabilistic seismic hazard analysis
PSHA
framework permitting the identification, quantification and rational combination of uncertainties in
earthquakes' intensity, location, rate of recurrence and variations in ground motion (3.7) characteristics
3.12
probability of exceedance
probability that a variable (or that an event) exceeds a specified reference level given exposure time
EXAMPLE Example of probability of exceedance during a given exposure time is the annual probability of
exceedance of a specified magnitude of ground acceleration, ground velocity or ground displacement.
3.13
response spectrum
function representing the peak elastic response for single degree of freedom oscillators with a specific
damping ratios in terms of absolute acceleration, pseudo velocity, or relative displacement values
against natural frequency or period of the oscillators
3.14
safety system
systems provided on the offshore structure to detect, control and mitigate hazardous situations
EXAMPLE Gas detection, emergency shutdown, fire protection, and their control systems.
3.15
sea floor
interface between the sea and the seabed (3.17)
3.16
seabed slide
failure of seabed (3.17) slopes
3.17
seabed
material below the sea floor (3.15) in which a structure is founded
3.18
seismic risk category
SRC
category defined from the exposure level and the expected intensity of seismic motions
© ISO 2017 – All rights reserved 3

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SIST EN ISO 19901-2:2018
ISO 19901-2:2017(E)

3.19
seismic hazard curve
curve showing the annual probability of exceedance (3.12) against a measure of seismic intensity
Note 1 to entry: The seismic intensity measures can include parameters such as peak ground acceleration,
spectral acceleration (3.22), or spectral velocity (3.23).
3.20
seismic reserve capacity factor
factor indicating the structure’s ability to sustain ground motions due to earthquakes beyond the level
of the ELE (3.5)
Note 1 to entry: The seismic reserve capacity factor is a structure specific property that is used to determine the
ELE acceleration from the ALE (3.1) acceleration.
3.21
site response analysis
wave propagation analysis permitting the evaluation of the effect of local geological and soil conditions
on the ground motions (3.7) as they propagate up from depth to the surface at the site
3.22
spectral acceleration
maximum absolute acceleration response of a single degree of freedom oscillator subjected to ground
motions (3.7) due to an earthquake
3.23
spectral velocity
maximum pseudo velocity response of a single degree of freedom oscillator subjected to ground motions
(3.7) due to an earthquake
Note 1 to entry: The pseudo velocity spectrum is computed by factoring the displacement or acceleration spectra
by the oscillator’s circular frequency or the inverse of its frequency, respectively. The pseudo spectrum is either
relative or absolute, depending on the type of response spectra that is factored.
3.24
spectral displacement
maximum relative displacement response of a single degree of freedom oscillator subjected to ground
motions (3.7) due to an earthquake
3.25
static pushover method
static pushover analysis
application and incremental increase of a global static pattern of actions on a structure, including
equivalent dynamic inertial actions, until a global failure mechanism occurs
3.26
tsunami
long period sea waves caused by rapid vertical movements of the sea floor (3.15)
Note 1 to entry: The vertical movement of the sea floor is often associated with fault rupture during earthquakes
or with seabed slides (3.16).
4 © ISO 2017 – All rights reserved

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SIST EN ISO 19901-2:2018
ISO 19901-2:2017(E)

4 Symbols and abbreviated terms
4.1 Symbols
a slope of the seismic hazard curve
R
C site coefficient, a correction factor applied to the acceleration part (shorter periods) of a
a
response spectrum
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; see Formulae (7) and (10)
r
C site coefficient, a correction factor applied to the velocity part (longer periods) of a
v
response spectrum
s undrained shear strength of the soil
u
s̅ average undrained shear strength of the soil in the effective seabed
u
D scaling factor for damping
G low amplitude shear modulus of the soil
max
g accelerati
...