ISO/FDIS 18954

ISO/TC 167
Secretariat: SN
Date: 2025-12-032026-01-14
Steel structures – — Structural bolting –— Test method to determine
parameters of bolt tightening procedures
Structures en acier – — Boulonnerie de construction métallique -— Méthode d'essai pour déterminer les
paramètres des procédures de serrage des boulons
FDIS stage
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ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 General . 3
6 Mechanical properties of bolting components . 7
7 Fitness for purpose test . 7
7.1 General . 7
7.2 Test apparatus . 7
7.3 Test assemblies. 8
7.4 Test set-up . 8
7.5 Test procedure . 9
7.6 Evaluation of the test results . 10
7.7 Requirements for suitability . 12
7.8 Test report . 13
8 Determination of tightening parameters . 14
8.1 General . 14
8.2 Criteria for the determination of the tightening parameters . 14
Bibliography . 17

iii
Foreword
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iv
Introduction
This document has been prepared to provide provisions and guidance in the testing of bolting assemblies for
pretensioning for which no tightening parameters exist, e.g. when bolts are pretensioned by turning the head,
for pretensioning of stainless steel bolting assemblies, when bolts need to be tightened in tapped holes or
when a special lubrication is used. This document gives provisions and guidance on how to qualify those
bolting assemblies for pretensioning and on how to determine secure tightening parameters.
v
Steel structures – — Structural bolting –— Test method to determine
parameters of bolt tightening procedures
1 Scope
This document specifies a test method to determine parameters of bolt tightening procedures for
pretensioned bolted connections to be used in structural steelwork.
The methods to establish bolt tightening procedures given in this document are applicable to pretensioned
bolted connections for which no approved tightening parameters exist in national or international standards.
For example, in cases where bolting assemblies have to be tightened by turning the head instead of the nut,
when conditions deviate from a given harmonized standard for pretensioning of bolting assemblies, or when
stainless steel bolting assemblies are to be pretensioned. In these cases, tightening parameters as well as
tightening procedures can be determined with the use of the Bolt Tightening Qualification Procedure (BTQP)
given in this document.
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 17607-1, Steel structures — Execution of structural steelwork — Part 1: General requirements and terms
and definitions
ISO 3506-1, Fasteners - — Mechanical properties of corrosion-resistant stainless steel fasteners - — Part 1: Bolts,
screws and studs with specified grades and property classes
ISO 3506-2, Fasteners - — Mechanical properties of corrosion-resistant stainless steel fasteners - — Part 1: Bolts,
screws and studs 2: Nuts with specified grades and property classes
ISO 3506-7, Fasteners - — Mechanical properties of corrosion-resistant stainless steel fasteners - — Part 7: Flat
washers with specified grades and property classes
ISO 898-1, Mechanical properties of fasteners made of carbon steel and alloy steel - — Part 1: Bolts, screws and
studs with specified property classes - — Coarse thread and fine pitch thread
ISO 898-2, Fasteners - — Mechanical properties of fasteners made of carbon steel and alloy steel - — Part 2: Nuts
with specified property classes
ISO 898-3, Mechanical properties of fasteners made of carbon steel and alloy steel - — Part 3: Flat washers with
specified property classes
3 Terms, and definitions and abbreviated terms
For the purposes of this document, the terms given in ISO 17607-1:2023 and the following terms and
definitions 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
manufacturing lot
quantity of structural bolting components of a single designation including product grade, property class and
size, manufactured from bar, wire, rod or flat product from a single cast, processed through the same or similar
steps at the same time or over a continuous time period, and through the same heat treatment and coating
process, if any
[SOURCE: ISO 17607-1:2023, 3.5.6]
3.1 3.2
bolting assembly lot
bolting assemblies tested and supplied together as a set comprising:
— — bolts from a single manufacturing lot (3.1);;
— — nuts from a single manufacturing lot;
— — washers from a single manufacturing lot
3.2 3.3
snug tight condition
condition that exists when all of the plies in a connection have been pulled into firm contact by the bolts in the
joint and all of the bolts in the joint have been tightened sufficiently to prevent the removal of the nuts without
the use of a wrench
Note 1 to entry: For pretensioned and slip-resistant joints, it is additionally the tightness of a bolt achieved by a few
impacts of an impact wrench, by the full effort of a person using a standard podger spanner or by application of an electric
torque wrench until the wrench starts to slow.
[SOURCE: ISO 17607-1:2023, 3.5.18 –, modified –— Note 1 to entry modified, use of electric torque wrench
was added].]
3.3 3.4
pretensioning
DEPRECATED: preloading
method of installing bolts with a minimum specified pretension
[SOURCE: ISO 17607-1:2023, 3.5.30 –, modified –— definition changed to emphasize method, Note 1 to entry
deleted].]
4 Symbols
A nominal stress area of the bolt, (mm )
s
d nominal bolt diameter, (mm)
F bolt force during the test, (kN)
b
F individual value of the bolt force related to a given nut rotation, torque or bolt elongation, (kN)
bi
F individual value of the maximum bolt force reached during the test, (kN)
bi,max
F mean value of F values, (kN)
bi,m bi
F nominal pretension level F = 0,7 ∙ f ∙ A
p,c p,C ub s
F specified pretension level below or equal to F = 0,7 ∙ f ∙ A (kN)
p p,C ub s
F the individual value of the bolt force F related to the considered tightening parameter (kN)
tpi p
F the minimum value of all F values (kN)
tp,min tpi
F the maximum value of all F values (kN)
tp,max tpi
F the mean value of all F values (kN)
tp,m tpi
F the 5 % fractile of all F values (kN)
tp,5 % tpi
F the 95 % fractile of all F values (kN)
tp,95 % tpi
f nominal tensile strength of the bolt material, (MPa)
ub
k individual value of the k-factor M/(d∙F )
i p
k mean value of the individual values of the k-factor of one test series
m
k the quantile factor according to Table 3Table 3
n
M tightening torque (Nm)
n the amount of test results within a test series
s standard deviation of a characteristic considered for a series of tests
F
V coefficient of variation of a characteristic considered for a series of tests
F
θ angle of rotation of the nut relative to the bolt, starting from a pretension of F = 2 kN (°)
b
θ individual value of the angle θ related to the considered tightening parameter, starting from a
tpi
pretension of F = 2 kN (°)
b
θ individual value of the angle θ at which the bolt force has first reached the value of F , starting
pi p
from a pretension of F = 2 kN (°)
b
θ individual value of the angle θ at which the bolt force has reached its maximum value F ,
1i bi, max
starting from a pretension of F = 2 kN (°)
b
θ individual value of the angle θ at which the test is stopped, starting from a pretension of F = 2 kN
2i b
(°)
∆θ individual angle difference (θ - θ ), (°)
1i 1i pi
∆θ individual angle difference (θ - θ ), (°)
2i 2i pi
∆θ minimum required value of the angle difference ∆θ as specified in the relevant product standard
2i,min 2i
respectively Table 2Table 2 (°)
Σt clamp length given as the total thickness of the clamped parts between the nut bearing face and
the bolt head bearing face, (mm)
5 General
The given procedure in this document only applies if no rules and parameters for tightening exist, e.g. when
bolts are pretensioned by turning the head, for pretensioning of stainless steel bolting assemblies, when bolts
need to be tightened in tapped holes or when a special lubrication is used.
The test method to establish bolt tightening procedures (Bolt Tightening Qualification Procedure) provides
design and execution rules for pretensioning of stainless steel, carbon and alloy steel bolting assemblies with
bolting assemblies consisting of one bolt, one nut, and washers as required for the installation method. One
washer should be installed between the clamped parts and the bolt head and the other washer should be
installed between the clamped parts and the nut. Within the BTQP, clamped parts are represented by the Bolt
Tension Measurement Device (BTMD).
The given Bolt Tightening Qualification Procedure allows the determination of the tightening parameters for
only one configuration. In this procedure, one configuration is:
— — one single bolting assembly lot (i.e. bolts from one manufacturing lot, nuts from one manufacturing
lot, washers from one manufacturing lot);
— — one lubricant;
— — one tightening method, with definition of the part to be rotated and the required pretension level.
The BTQP is only valid for the inspected configuration and should be performed for each new configuration.
The specified pretension F shall not exceed the nominal pretension level F .
p p,C
The BTQP includes:
— — the definition of appropriate lubrication to ensure a sufficiently long plastic plateau of the bolt force–
rotation curve where ∆θ ≥ ∆θ (the ability to demonstrate the required functional characteristics of
2i 2i,min
the bolting assembly is highly dependent on the type of lubrication used);
— — a suitability test to confirm that the required pretension can be reliably obtained by a specific
tightening method with a sufficient margin of safety against overtightening;
— — the evaluation of tightening parameters.
A schematic overview of the BTQP is given in Figure 1Figure 1. The detailed parameters and requirements
are given in Clause 6Clause 6 to Clause 8Clause 8.
De�initionof initial parameters for pretensioning
Product Standard Lubrication Tightening Method Target pretensionF Other properties
p
• ISO 4014 Selection of a • Torque method • Target level I or II • Property class
• ISO 4017 lubricant which • Combined method • Required pretension • Coating system
• ISO 4762 is recommended • Turn of nut method base on design • etc.
• etc. for the • Hydraulic Tensioni
...