ISO 19905-1:2012

Petroleum and natural gas industries - Site-specific assessment of mobile offshore units - Part 1: Jack-ups

ISO 19905-1:2012 specifies requirements and guidance for the site-specific assessment of independent leg jack‑up units for use in the petroleum and natural gas industries. It addresses manned non-evacuated, manned evacuated and unmanned jack‑ups; the installed phase at a specific site. To ensure acceptable reliability, the provisions of ISO 19905-1:2012 form an integrated approach, which is used in its entirety for the site-specific assessment of a jack‑up. ISO 19905-1:2012 does not apply specifically to mobile offshore drilling units operating in regions subject to sea ice and icebergs. When assessing a jack-up operating in such areas, it is intended that the assessor supplement the provisions of ISO 19905-1:2012 with the provisions relating to ice actions and procedures for ice management contained in ISO 19906. ISO 19905-1:2012 does not address design, transportation to and from site, or installation and removal from site. However, it is advisable that the assumptions used in the assessment be checked against the as-installed configuration. To ensure that the design of the jack‑up is sound and the structure is adequately maintained, ISO 19905-1:2012 is applicable only to independent leg jack‑ups that either: hold a valid classification society certification from a recognized classification society (RCS) throughout the duration of the operation at the specific site subject to assessment, or have been verified by an independent competent body to be structurally fit for purpose for elevated situations and are subject to periodic inspection, both to the standards of an RCS. Jack‑ups that do not comply with this requirement are assessed according to the provisions of ISO 19902, supplemented by methodologies from ISO 19905-1:2012, where applicable.

Industries du pétrole et du gaz naturel — Évaluation spécifique au site d'unités mobiles en mer — Partie 1: Plates-formes auto-élévatrices

General Information

• Status: Withdrawn
• Publication Date: 24-Jul-2012
• Withdrawal Date: 24-Jul-2012
• ICS: 75.180.10 - Exploratory, drilling and extraction equipment
• Technical Committee: ISO/TC 67/SC 7 - Offshore structures
• Drafting Committee: ISO/TC 67/SC 7/WG 7 - Site specific assessment of mobile offshore units (MOUS)
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 15-Jan-2016
• Completion Date: 13-Dec-2025

Relations

• Consolidates: ISO 8434-5:1995 - Metallic tube connections for fluid power and general use - Part 5: Test methods for threaded hydraulic fluid power connections
• Effective Date: 06-Jun-2022
• Revised: ISO 19905-1:2016 - Petroleum and natural gas industries - Site-specific assessment of mobile offshore units - Part 1: Jack-ups
• Effective Date: 04-Nov-2015

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 19905-1
First edition
2012-08-01
Petroleum and natural gas industries —
Site-specific assessment of mobile
offshore units —
Part 1:
Jack-ups
Industries du pétrole et du gaz naturel — Évaluation spécifique au site
d'unités mobiles en mer —
Partie 1: Plates-formes auto-élévatrices

Reference number
©
ISO 2012
©  ISO 2012
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
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Published in Switzerland
ii © ISO 2012 – All rights reserved

Contents Page
Foreword . v
Introduction . vii
1  Scope . 1
2  Normative references . 2
3  Terms and definitions . 2
4  Symbols and abbreviated terms . 13
4.1  Symbols . 13
4.2  Abbreviated terms . 14
5  Overall considerations . 15
5.1  General . 15
5.2  Assessment approach . 16
5.3  Selection of limit states . 18
5.4  Determination of assessment situations . 18
5.5  Exposure levels . 20
5.6  Analytical tools . 23
6  Data to assemble for each site . 24
6.1  Applicability . 24
6.2  Jack-up data . 24
6.3  Site and operational data . 24
6.4  Metocean data . 24
6.5  Geophysical and geotechnical data . 25
6.6  Earthquake data . 26
7  Actions. 26
7.1  Applicability . 26
7.2  General . 26
7.3  Metocean actions . 27
7.4  Functional actions . 28
7.5  Displacement dependent effects . 28
7.6  Dynamic effects . 28
7.7  Earthquakes . 28
7.8  Other actions . 28
8  Structural modelling . 28
8.1  Applicability . 28
8.2  Overall considerations . 28
8.3  Modelling the leg . 29
8.4  Modelling the hull . 30
8.5  Modelling the leg-to-hull connection . 30
8.6  Modelling the spudcan and foundation . 31
8.7  Mass modelling . 32
8.8  Application of actions . 32
9  Foundations . 35
9.1  Applicability . 35
9.2  General . 35
9.3  Geotechnical analysis of independent leg foundations . 36
9.4  Other considerations . 39
10  Structural response . 41
10.1  Applicability . 41
10.2  General considerations .41
10.3  Types of analyses and associated methods .41
10.4  Common parameters .42
10.5  Storm analysis .44
10.6  Fatigue analysis .47
10.7  Earthquake analysis .47
10.8  Accidental situations .47
10.9  Alternative analysis methods .48
11  Long-term applications .48
11.1  Applicability .48
11.2  Assessment data .48
11.3  Special requirements .49
11.4  Survey requirements .50
12  Structural strength.50
12.1  Applicability .50
12.2  Classification of member cross-sections .51
12.3  Section properties of non-circular prismatic members .52
12.4  Effects of axial force on bending moment .53
12.5  Strength of tubular members .53
12.6  Strength of non-circular prismatic members .53
12.7  Assessment of joints .53
13  Acceptance criteria .54
13.1  Applicability .54
13.2  General formulation of the assessment check .55
13.3  Leg strength assessment .55
13.4  Spudcan strength assessment .56
13.5  Holding system strength assessment .56
13.6  Hull elevation assessment .56
13.7  Leg length reserve assessment .56
13.8  Overturning stability assessment .57
13.9  Foundation integrity assessment .57
13.10  Interaction with adjacent infrastructure .58
13.11  Temperatures .59
Annex A (informative) Additional information and guidance .60
Annex B (normative) Summary of partial action and partial resistance factors . 238
Annex C (informative) Additional information on structural modelling and response analysis . 240
Annex D (informative) Foundations — Recommendations for the acquisition of site-specific
geotechnical data. 250
Annex E (informative) Foundations — Additional information and alternative approaches . 256
Annex F (informative) Informative annex on Clause A.12 — Structural strength . 269
Annex G (informative) Contents list for typical site-specific assessment report . 283
Annex H (informative) Regional information . 290
Bibliography . 299

iv © ISO 2012 – All rights reserved

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 19905-1 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.
ISO 19905 consists of the following parts, under the general title Petroleum and natural gas industries — Site-
specific assessment of mobile offshore units:
 Part 1: Jack-ups
 Part 2: Jack-ups commentary and detailed sample calculation [Technical Report]
The following part is under preparation:
 Part 3, dealing with the site-specific assessment of mobile floating units.
ISO 19905 is one of a series of International Standards for offshore structures. The full series consists of the
following International Standards:
 ISO 19900, Petroleum and natural gas industries — General requirements for offshore structures
 ISO 19901-1, Petroleum and natural gas industries — Specific requirements for offshore structures —
Part 1: Metocean design and operating considerations
 ISO 19901-2, Petroleum and natural gas industries — Specific requirements for offshore structures —
Part 2: Seismic design procedures and criteria
 ISO 19901-3, Petroleum and natural gas industries — Specific requirements for offshore structures —
Part 3: Topsides structure
 ISO 19901-4, Petroleum and natural gas industries — Specific requirements for offshore structures —
Part 4: Geotechnical and foundation design considerations
 ISO 19901-5, Petroleum and natural gas industries — Specific requirements for offshore structures —
Part 5: Weight control during engineering and construction
 ISO 19901-6, Petroleum and natural gas industries — Specific requirements for offshore structures —
Part 6: Marine operations
 ISO 19901-7, Petroleum and natural gas industries — Specific requirements for offshore structures —
Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units
1)
 ISO 19901-8 , Petroleum and natural gas industries — Specific requirements for offshore structures —
Part 8: Marine soils investigations
 ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
 ISO 19903, Petroleum and natural gas industries — Fixed concrete offshore structures
 ISO 19904-1, Petroleum and natural gas industries — Floating offshore structures — Part 1: Monohulls,
semi-submersibles and spars
 ISO 19905-1, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
units — Part 1: Jack-ups
 ISO/TR 19905-2, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
units — Part 2: Jack-ups commentary and detailed sample calculation
2 )
, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
 ISO 19905-3
units — Part 3: Floating units
 ISO 19906, Petroleum and natural gas industries — Arctic offshore structures

1) Under preparation. It is also expected that there will be further parts of ISO 19901.
2) Under preparation.
vi © ISO 2012 – All rights reserved

Introduction
The series of International Standards applicable to types of offshore structure, ISO 19900 to ISO 19906,
addresses design requirements and assessments for 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 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.
[7]
This part of ISO 19905, which has been developed from SNAME Technical & Research Bulletin 5-5A , states
the general principles and basic requirements for the site-specific assessment of mobile jack-ups; it is
intended to be used for assessment and not for design.
NOTE For the exposure level 1(L1) assessment and, where appropriate, the exposure level 2 (L2) assessment prior
to evacuation being effected, this part of ISO 19905 requires the use of 50 year independent or 100 year joint probability
metocean extremes, together with associated partial action factors. It is based on extensive benchmarking and best
practice in the international community.
Site-specific assessment is normally carried out when an existing jack-up unit is to be installed at a specific
site. The assessment is not intended to provide a full evaluation of the jack-up; it assumes that aspects not
addressed herein have been addressed using other practices and standards at the design stage. In some
instances, the original design of all or part of the structure could be in accordance with other standards in the
ISO 19900 series, and in some cases, different practices or standards could have been applied.
The purpose of the site assessment is to demonstrate the adequacy of the jack-up and its foundations for the
assessment situations and defined limit states, taking into account the consequences of failure. It is important
that the results of a site-specific assessment be appropriately recorded and communicated to those persons
required to know or act on the conclusions and recommendations. Alternative approaches to the site-specific
assessment can be used, provided that they have been shown to give a level of structural reliability equivalent,
or superior, to that implicit in this part of ISO 19905.
Annex A provides background to and guidance on the use of this part of ISO 19905. The clause numbering in
Annex A is the same as in the normative text in order to facilitate cross-referencing. ISO/TR 19905-2 provides
additional background to some clauses and a detailed sample 'go-by' calculation.
Annex B summarizes the partial factors. Supplementary information is presented in Annexes C to H.
To meet certain needs of industry for linking software to specific elements in this part of ISO 19905, a special
numbering system has been permitted for figures, tables, equations and bibliographic references.
In 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.
viii © ISO 2012 – All rights reserved

INTERNATIONAL STANDARD ISO 19905-1:2012(E)

Petroleum and natural gas industries — Site-specific
assessment of mobile offshore units —
Part 1:
Jack-ups
1 Scope
This part of ISO 19905 specifies requirements and guidance for the site-specific assessment of independent
leg jack-up units for use in the petroleum and natural gas industries. It addresses
a) manned non-evacuated, manned evacuated and unmanned jack-ups;
b) the installed phase at a specific site.
To ensure acceptable reliability, the provisions of this part of ISO 19905 form an integrated approach, which is
used in its entirety for the site-specific assessment of a jack-up.
This part of ISO 19905 does not apply specifically to mobile offshore drilling units operating in regions subject
to sea ice and icebergs. When assessing a jack-up operating in such areas, it is intended that the assessor
supplement the provisions of this part of ISO 19905 with the provisions relating to ice actions and procedures
for ice management contained in ISO 19906.
This part of ISO 19905 does not address design, transportation to and from site, or installation and removal
from site. However, it is advisable that the assumptions used in the assessment be checked against the
as-installed configuration.
To ensure that the design of the jack-up is sound and the structure is adequately maintained, this part of
ISO 19905 is applicable only to independent leg jack-ups that either
 hold a valid classification society certification from a recognized classification society (RCS) throughout
the duration of the operation at the specific site subject to assessment; or
 have been verified by an independent competent body to be structurally fit for purpose for elevated
situations and are subject to periodic inspection, both to the standards of an RCS.
NOTE 1 An RCS is an International Association of Classification Societies (IACS) member body, meeting the RCS
definition given in 3.52.
Jack-ups that do not comply with this requirement are assessed according to the provisions of ISO 19902,
supplemented by methodologies from this part of ISO 19905, where applicable.
NOTE 2 Future revisions of this part of ISO 19905 can be expanded to cover mat-supported jack-ups.
NOTE 3 Well conductors are a safety-critical element for jack-up operations. However, the integrity of well conductors
is not part of the site-specific assessment process for jack-ups and is, therefore, not addressed in this part of ISO 19905.
Annex A provides references to other publications addressing this topic.
NOTE 4 RCS rules and the IMO MODU code provide guidance for the design of jack-ups.
2 Normative references
The following referenced documents are indispensable for the application 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 19901-1, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 1:
Metocean design and operating conditions
ISO 19901-2, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 2:
Seismic design procedures and criteria
ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 19900, ISO 19901-1, ISO 19901-2
3)
and ISO 19902, and the following apply.
3.1
abnormal wave crest
3 4
wave crest with probability of typically 10 to 10 per annum
3.2
accidental situation
exceptional situation of the structure
EXAMPLE Impact; fire; explosion; local failure; loss of intended differential pressure (e.g. buoyancy).
3.3
action
external load applied to the structure (direct action) or an imposed deformation or acceleration (indirect action)
EXAMPLE An imposed deformation can be caused by fabrication tolerances, settlement, temperature change or
moisture variation.
NOTE An earthquake typically generates imposed accelerations.
[ISO 19900:2002, definition 2.1]
3.4
assessment
site-specific assessment
evaluation of the stability and structural integrity of a jack-up and, where applicable, its seabed restraint or
support against the actions determined in accordance with the requirements of this part of ISO 19905
NOTE An assessment can be limited to an evaluation of the components or members of the structure which, when
removed or damaged, could cause failure of the whole structure, or a significant part of it.
3.5
assessment situation
jack-up configuration together with the environmental loading to be assessed
NOTE 1 For discussion on configuration, see 5.4.1.
NOTE 2 The assessment situations are checked against the acceptance criteria of this part of ISO 19905 to
demonstrate that the relevant limit states are not exceeded.

3) Other terms and definitions relevant for the use of this part of ISO 19905 are also found in ISO 19901-4 and
ISO 19906.
2 © ISO 2012 – All rights reserved

3.6
assessor
entity performing the site-specific assessment
3.7
backfill
submerged weight of all of the soil that can be present on top of the spudcan
NOTE Backfilling can occur during or after preloading. W refers to the submerged weight of the backfilling that
BF,o
occurs up to achieving the preload reaction. W refers to the submerged weight of the backfilling that occurs after the
BF,A
maximum preload has been applied and held. Both W and W can comprise backflow and/or infill. For discussion of
BF,o BF,A
the effects, see A.9.3.2.1.4.
3.8
backflow
soil that flows from beneath the spudcan around the sides and onto the top
NOTE Backflow is part of backfill (3.7).
3.9
basic variable
one of a specified set of variables representing physical quantities which characterize actions, environmental
influences, geometrical quantities, or material properties including soil properties
[ISO 19900:2002, definition 2.5]
3.10
boundary conditions
actions and constraints on a (section of a) structural component (or a group of structural components) by other
structural components or by the environment surrounding it
NOTE Boundary conditions can be used to generate reaction forces at locations of restraint.
[ISO 19902:2007, definition 3.6]
3.11
chart datum
local datum used to fix water depths on a chart or tidal heights over an area
NOTE Chart datum is usually an approximation to the level of the lowest astronomical tide.
[ISO 19901-1:2005, definition 3.2]
3.12
consequence category
classification system for identifying the environmental, economic and indirect personnel safety consequences
of failure of a jack-up
NOTE 1 Categories for environmental and economic consequences are the following (see 5.3.3):
 C1: high environmental or economic consequence;
 C2: medium environmental or economic consequence;
 C3: low environmental or economic consequence.
NOTE 2 Adapted from ISO 19902:2007, definition 3.11.
3.13
critical component
structural component, failure of which could cause failure of the whole structure, or a significant part of it
NOTE A critical component is part of the primary structure.
[ISO 19902:2007, definition 3.12]
3.14
dynamic amplification factor
DAF
ratio of a dynamic action effect to the corresponding static action effect
NOTE 1 For a jack-up, the dynamic action effect is best simulated by means of a concentrated or distributed inertial
loadset. It is usually not appropriate to factor the static actions to simulate the effects of dynamic actions.
NOTE 2 The DAF excluding the mean values, K , can typically be obtained from a single degree-of-freedom
DAF,SDOF
(SDOF) calculation. In this case, it is defined as the ratio of the amplitude of a dynamic action effect to the amplitude of the
corresponding static action effect for periodic excitation of a linear one degree-of-freedom model approximation of jack-up
behaviour.
NOTE 3 The DAF including the mean values, K , can typically be obtained from a random wave calculation.
DAF,RANDOM
In this case, it is defined as the ratio of the absolute value of a dynamic action effect to the absolute value of the
corresponding static action effect, each including their mean value.
NOTE 4 Adapted from ISO 19902:2007, definition 3.16.
3.15
deterministic analysis
analysis in which the response is determined from a single combination of actions
3.16
exposure level
classification system used to define the requirements for a structure based on consideration of life-safety and
of environmental and economic consequences of failure
NOTE 1 An exposure level 1 (L1) jack-up is the most critical and exposure level 3 (L3) the least (see 5.5).
NOTE 2 Adapted from ISO 19902:2007, definition 3.18.
3.17
extreme storm event
extreme combination of wind, wave and current conditions to which the structure can be subjected during its
deployment
NOTE This is the metocean event used for ULS storm assessment (see 6.4).
3.18
fixed load
permanent parts of the jack-up, including hull, legs and spudcans, outfit, stationary and moveable-fixed
equipment
NOTE Moveable-fixed equipment normally includes the drilling package structure and associated permanently
attached equipment.
3.19
footprint
sea floor depression which remains when a jack-up is removed from a site
3.20
foundation
soil and spudcan supporting a jack-up leg
4 © ISO 2012 – All rights reserved

3.21
foundation fixity
rotational restraint offered by the soil to the spudcan
3.22
foundation stability
ability of the foundation to provide sufficient support to remain stable when subjected to actions and
incremental deformation
3.23
global analysis
determination of a consistent set of internal forces and moments, or stresses, in a structure that are in
equilibrium with a defined set of actions on the entire structure
NOTE 1 When a global analysis is of a transient situation (e.g. earthquake), the inertial response is part of the
equilibrium.
NOTE 2 Adapted from ISO 19902:2007, definition 3.23.
3.24
independent leg jack-up
jack-up unit with legs that can be raised and lowered independently
3.25
inertial loadset
set of actions that approximates the effect of the inertial forces
NOTE An inertial loadset is used only in quasi-static analyses.
3.26
infill
soil above the plan area of the spudcan arising from sediment transport or hole sidewall collapse
NOTE Infill is part of backfill (3.7).
3.27
intrinsic wave frequency
wave frequency of a periodic wave in a reference frame that is stationary with respect to the wave
NOTE If there is no current, the reference frame is also stationary with respect to the sea floor. If there is a current,
the reference frame moves with the same speed and in the same direction as the current.
3.28
jack-up
mobile offshore unit with a buoyant hull and one or more legs that can be moved up and down relative to the
hull
NOTE A jack-up reaches its operational mode by lowering the leg(s) to the seabed and then raising the hull to the
required elevation. The majority of jack-ups have three or more legs, each of which can be moved independently and
which are supported in the seabed by spudcans.
3.29
jack-up owner
representative of the companies owning or chartering the jack-up
3.30
joint probability metocean data
combinations of wind, wave and current that produce the action effect that can be expected to occur at a site,
on average, once in the return period
3.31
leaning instability
instability of an independent leg jack-up that can arise when the rate of increase of actions on the foundation
with jack-up inclination exceeds the rate of increase of foundation capacity with depth
3.32
life-safety category
classification system for identifying the applicable level of life-safety of personnel on a jack-up
NOTE 1 Categories for life-safety are the following (see 5.5.2):
 S1: manned non-evacuated;
 S2: manned evacuated;
 S3: unmanned.
NOTE 2 Adapted from ISO 19902:2007, definition 3.27.
3.33
limit state
state beyond which the structure no longer fulfils the relevant assessment criteria
NOTE Adapted from ISO 19900:2002, definition 2.21.
3.34
load case
compatible load arrangements, sets of deformations and imperfections considered simultaneously with
permanent actions and fixed variable actions for a particular design or verification
[ISO 19902:2007, definition 3.29]
3.35
long-term operation
operation of a jack-up on one particular site for more than the normal RCS special survey period of five years
3.36
lowest astronomical tide
LAT
level of low tide when all harmonic components causing the tides are in phase
NOTE The harmonic components are in phase approximately once every 19 years, but these conditions are
approached several times each year.
[ISO 19901-1:2005, definition 3.12]
3.37
mat-supported jack-up
jack-up unit with the leg(s) rigidly connected by a foundation structure, such that the leg(s) are raised and
lowered in unison
3.38
mean high water spring tidal level
arithmetic mean of all high water spring tidal sea levels measured over a long period, ideally 19 years
3.39
mean low water spring tidal level
arithmetic mean of all low water spring tidal sea levels measured over a long period, ideally 19 years
6 © ISO 2012 – All rights reserved

3.40
mean sea level
MSL
arithmetic mean of all sea levels measured at hourly intervals over a long period, ideally 19 years
NOTE Seasonal changes in mean level can be expected in some regions and over many years the mean sea level
can change.
[ISO 19901-1:2005, definition 3.15]
3.41
mean zero-upcrossing period
average intrinsic period of the zero-upcrossing waves in a sea state
NOTE 1 In practice, the mean zero-crossing period is often estimated from the zeroth and second moments of the
wave spectrum as given by Equation (3.41-1):
TT mfmf() ()2 m ()m () . (3.41-1)
z2 0 2 0 2
where
f is the frequency in cycles per second (hertz);
m is the zeroth spectral moment and is equivalent to σ , the variance of the corresponding time series;
m is the second spectral moment;
T and T are the average zero-crossing period of the water surface elevation, defined by the zeroth and second
2 z
order spectral moments, (T = T );
2 z
ω is the wave frequency in radians per second.
NOTE 2 Adapted from ISO 19901-1:2005, definition 3.17.
3.42
most probable maximum extreme
MPME
value of the maximum of a variable with the highest probability of occurring over a defined period of time
NOTE 1 A defined period of time can be, for example, X hours.
NOTE 2 The most probable maximum extreme is the value for which the probability density function of the maxima of
the variable has its peak. It is also called the mode or modus of the statistical distribution.
NOTE 3 Adapted from ISO 19901-1:2005, definition 3.19.
3.43
nominal strength
strength calculated for a cross-sectional area, taking into account the stress raising effects of the macro-
geometrical shape of the component of which the section forms a part, but disregarding the local stress raising
effects from the section shape and any weldment or other fixing detail
NOTE Adapted from ISO 19902:2007, definition 3.34.
3.44
nominal stress
stress calculated in a sectional area, including the stress raising effects of the macro-geometrical shape of the
component of which the section forms a part, but disregarding the local stress raising effects from the section
shape and any weldment or other fixing detail
NOTE Overall elastic behaviour is assumed when calculating nominal stresses.
[ISO 19902:2007, definition 3.34]
3.45
operating manual
marine operations manual
manual that defines the operational characteristics and capabilities of the jack-up in accordance with the IMO
MODU code
NOTE The assessor is advised to ensure that the operations manual referenced is the latest revision and that any
updated weight data are provided.
3.46
operator
representative of the companies leasing the site
NOTE The operator is normally the oil company acting on behalf of co-licensees.
3.47
preloading
installation of the spudcans by vertical loading of the soil beneath a jack-up leg spudcan with the objective of
ensuring sufficient foundation capacity under assessment situations through to the time when the maximum
load is applied and held
NOTE Whilst three-legged jack-ups preload by taking water ballast on board, jack-ups with four or more legs typically
achieve foundation preload by carrying the hull weight on pairs of legs in turn. This procedure is known as pre-driving and
generally does not require the addition of water ballast. For the purposes of this part of ISO 19905, no distinction is made
between preload and pre-drive.
3.48
preload reaction
maximum vertical reaction under a spudcan, V , supporting the in-water weight of the jack-up during the
Lo
entire preloading operation
NOTE 1 The in-water weight is the full weight of the hull, variable load and preload ballast, plus the legs and spudcans
and any contained water, reduced by the buoyancy in water of the legs and spudcans (calculated from their external
dimensions). Soil buoyancy and the weight of any soil backfill above the spudcan are neglected. It is necessary to take
care when accounting for water contained in the spudcan (in some cases this can be included in the quoted leg weight).
NOTE 2 This is the maximum reaction on a spudcan, V , that would be obtained during preloading if the jack-up were
Lo
installed on an infinitely rigid foundation.
3.49
punch-through
rapid, uncontrolled vertical leg movement due to soil failure in strong soil overlying weak soil
3.50
quasi-static
static representation of a dynamic process
NOTE In some cases, the influence of structural accelerations can be approximated by using an equivalent inertial
loadset.
3.51
rack phase difference
RPD
relative difference in the position of adjacent leg chords within a leg measured parallel to the longitudinal axis
of the chords
NOTE This is the out-of-plane distortion of the plan-frame.
8 © ISO 2012 – All rights reserved

3.52
recognized classification society
RCS
member of the international association of classification societies (IACS), with recognized and relevant
competence and experience in jack-ups, and with established rules and procedures for
classification/certification of such installations used in petroleum-related activities
NOTE Adapted from ISO 19901-7:2005, definition 3.23.
3.53
redundancy
ability of a structure to find alternative load paths following failure of one or more non-critical components, thus
limiting the consequences of such failures
NOTE All structures having redundancy are statically indeterminate.
[ISO 19902:2007, definition 3.39]
3.54
regulator
authority established by a national governmental administration to oversee the activities of the offshore oil and
natural gas industries within its jurisdiction, with respect to the overall safety to life and protection of the
environment
NOTE 1 The term regulator can encompass more than one agency in any particular territorial waters.
NOTE 2 The regulator can appoint other agencies, such as marine classification societies, to act on its behalf, and in
such cases, the term regulator within this part of ISO 19905 includes such agencies.
NOTE 3 Within this part of ISO 19905, the term regulator does not include any agency responsible for approvals to
extract hydrocarbons, unless such agency also has responsibility for safety and environmental protection.
NOTE 4 Adapted from ISO 19902:2007, definition 3.40.
3.55
representative value
value assigned to a basic variable for verification of a
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