ISO 18900:2025

International
Standard
ISO 18900
First edition
Steel structures — Structural
2025-11
bolting — Test method for
determining the slip factor for
faying surfaces of slip-resistant
connections
Structures en acier — Boulonnerie de construction métallique —
Méthode d’essai pour déterminer le coefficient de frottement des
surfaces en contact pour les assemblages résistant au glissement
Reference number
© ISO 2025
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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 . 1
5 General . 2
6 Significant variables . 2
7 Test specimens . 2
8 Slip test procedure and evaluation of results . 4
9 Extended creep test procedure and evaluation. 5
10 Test results . . 7
11 Test report . 8
Bibliography . 9

iii
Foreword
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iv
Introduction
This document has been prepared to provide provisions and guidance in the testing of slip-resistant
connections made of steel for providing slip factors to be used in structural steelwork.

v
International Standard ISO 18900:2025(en)
Steel structures — Structural bolting — Test method for
determining the slip factor for faying surfaces of slip-resistant
connections
1 Scope
This document specifies a procedure to determine the slip factor of faying surfaces in slip-resistant (friction)
connections to be used in structural steelwork.
The method is mainly applicable to uncoated and coated components made of steel with various surface
treatments.
This document applies mainly to carbon steels but can be used for other type of steels as appropriate.
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 17607-3, Steel structures — Execution of structural steelwork — Part 3: Fabrication
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 17607-1 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/
4 Symbols
F specified pretension of the bolts
p,C
F individual slip load
Si
F mean value of the slip load
Sm
n number of test specimens
s standard deviation s for the slip load from the first five specimens (ten values), expressed percentage
Fs
of the mean slip load value
s standard deviation for the slip load
Fs
s standard deviation for the slip factor
μ
μ characteristic value of the slip factor
μ individual slip factor
i
μ mean value of the slip factor
m
5 General
The purpose of this test is to determine the slip factor for a particular surface treatment, often involving a
surface coating.
The test procedure is intended to ensure that account is taken of the possibility of creep deformation of the
connection.
The validity of the test results is limited to cases where all significant variables are similar to those of the
test specimens.
6 Significant variables
The following variables shall be taken as significant on the test results:
a) property class of the bolt;
b) number and configuration of washers;
c) grade of steel plates;
d) composition of the coating;
e) maximum thickness of the coating;
f) surface treatment of the faying surfaces prior to coating and resulting surface conditions including
roughness and surface profile;
g) parameters of primary layers in case of multi-layer systems;
h) curing parameters.
7 Test specimens
The test specimens shall conform to the dimensional details shown in Figure 1.
The steel material shall conform to any structural steel between 350 MPa and 700 MPa minimum specified
yield strength, inclusive.
The plates shall have accurately cut edges that do not interfere with contact between the plate surfaces.
They shall be sufficiently flat to permit the prepared surfaces to be in contact when the bolts have been
pretensioned. The plate edges in contact with the testing machine shall be flat and parallel to the contact
surface.
Dimensions in millimetres
A A-A A A-A
S1
S1 S2 S2
b b
a 1 a
1 c
c
1 1
50 50
40 40 8
A
A
a) M20 bolts in 22 mm diameter hole b) M16 bolts in 18 mm diameter hole
Key
S1 slip plane 1
S2 slip plane 2
Figure 1 — Compression type test specimens for static slip factor test
The surface treatment and coating to be tested shall be applied to the contact surfaces of the test specimens
in a manner consistent with the intended structural application. The mean dry film thickness of the coating
on the contact surface of the test specimens, measured according to the relevant standard, shall be at least
25 % thicker than the nominal dry film thickness specified for use in the structure.
The curing procedure shall be documented, either by reference to published recommendations or by
description of the actual procedure.
The tolerances of the bolt holes shall conform with ISO 17607-3. Burrs and shear lips at bolt holes shall be
removed.
The specimens shall be assembled such that the bolts are bearing in the opposite direction to the applied force.
The time interval (in hours) between coating, assembling and testing shall be recorded.
The bolts shall be tightened to within ±5 % of the specified pretension, F , for the size and property class
p,C
of the bolt used.
The pretension in the bolts shall be directly measured with equipment that is accurate to ±4 %.
If it is required to estimate bolt pretension losses over time, the test specimens may be left for a specified
period at the end of which the pretensions may be again measured.
The bolt pretensions in each test specimen shall be measured just prior to testing and, if necessary, the bolts
shall be retightened to the required ±5 % accuracy.
The tension-type test specimen for creep test, as shown in Figure 2, is an alternative test setup for static
test. To ensure that the two inner plates have the same thickness, they shall be produced by cutting them
consecutively from the same piece of material and assembled in their original relative positions.
NOTE The compression-type and tension-type test specimen with one single bolt lead to comparable static slip
[2]
factors, even with those test specimens consisting of multiple bolts .

a , b , c
1 1 1
a , b , c
2 2 2
40 40
20 20
a , b , c
1 1 1
a , b , c
2 2 2
35 35
8 Slip test procedure and evaluation of results
In a first step, four static test specimens shall be tested in compression at a test speed such that the duration
of the test is approximately 10 min to 15 min. The specimens shall be tested in a universal testing machine.
The load-slip relationship shall be recorded.
The load-slip relationship can be determined from a tension-type test setup as an alternative test method,
as long as the contact surface area per bolt remains the same in comparison with test specimens presented
in Figure 2.
In the second step, the fifth test specimen shall be tested in tension in a creep test.
Dimensions in millimetres
A A-A A A-A
S1 S2
S2
S1
bb
a 1
1 c
1 1 b
a
1 c
50 50
40 40
A 80
A
a) M20 bolts in 22 mm hole diameter b) M16 bolts in 18 mm hole diameter
Key
1 specimen (in grey)
2 loose bolt
S1 slip plane 1
S2 slip plane 2
Figure 2 — Tension-type test specimen for creep test
In a test specimen, two slip planes exist: slip planes 1 and 2 according to Figure 1.
The slip shall be taken as the relative displacement between adjacent points on an inner plate (positions b
and b , Figure 1) and a cover plate (positions a , a ,c and c , Figure 1), in the direction of the applied load.
2 1 2 1 2
The slip displacement shall be measured on both sides of the specimen.
Slip occurs in a failure mode of combination of slip in slip planes 1 and 2. The slip must be evaluated according
to this failure mode, so that finally one mean
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