High strength structural bolting assemblies for preloading,
according to EN 14399.
Technical information for use.
Contents
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Scope
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Normative References
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General
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Symbols and units
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Assembly method
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Bolts
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Nuts
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Washers
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Tightening of preloaded bolts: HV system.
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Nominal minimum preloading force
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Tightening method, class K1
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Tightening method, class K0
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Inspection and testing of preloaded bolted connections
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Before tightening
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During and after tightening
7.2.1 Inspection of tightening by the combined method
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Recommendations
Annex A - Prescribed clamp lengths
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Scope
The information in this technical documentation are referred to high strength structural
bolting assemblies for preloading, according to the standards EN 14399-1, system HV,
classes K0 e K1.
General technical information about tightening of preloaded bolted joints, in E category,
according to the standards EN 1993-1-8: 2005 " Design of steel structures. Part 1-8: Design
of joints ", are specified.
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Normative References
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EN 1090-2: 2008 "Execution of steel structures and aluminium structures - Part 2:
Technical requirements for steel structures";
EN 1993-1-8: 2005 "Design of steel structures. Part 1-8: Design of joints";
EN 14399-1:2005 "High-strength structural bolting assemblies for preloading - Part 1:
General requirements";
EN 14399-2:2005 "High-strength structural bolting assemblies for preloading - Part 2:
Suitability test for preloading";
EN 14399-4:2005 "High-strength structural bolting assemblies for preloading - Part 4:
System HV. Hexagon bolt and nut assemblies";
EN 14399-6:2005 "High-strength structural bolting assemblies for preloading - Part 6:
Plain chamfered washers".
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General
Structural bolting assemblies (bolt/nut/washers) manufactured by Agrati are complying with
the requirements of the mandate M/120 (Structural metallic products and ancillaries) given
under the EU Construction Products Directive 89/106/EEC. This entitles the manufacturer to
affix the CE marking.
CE marking certifies:
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the compliance of the assemblies bolt/nut/washers with the harmonized European
standards for metallic constructions;
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the execution of a structured, controlled and certificated, by a notified external body,
production process;
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the presence of a quality management system able to guarantee a continuous surveillance,
assessment and approval of production process.
Every single Agrati HV assembly, ready to use, is a set comprising:
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a bolt, in compliance with the standard EN 14399-4;
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a properly lubricated nut, in compliance with the standard EN 14399-4;
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two washers, in compliance with the standards EN 14399-6;
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possible direct or indirect measurement of bolt preload device.
Agrati supplies assemblies in these two versions:
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hot dip galvanized;
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as processed (the normal finish resulting from manufacture with a light coating of oil).
Other coatings may be negotiated between the purchaser and the manufacturer.
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Symbols and units
References: EN 1993-1-8; EN 14399-2.
2
nominal stress area of the bolts, [mm ]
nominal thread diameter, [mm]
nominal minimum preloading force , [kN]
nominal tensile strength, [MPa]
individual value of the k-factor, (for K1 class: 0,10 0,16; for K0 class: not
specified)
k-factor value for the calculation of the tightening torque, (for class K1: = 0,13
unless otherwise specified - ref. EN 1090-2, § 8.5.4)
reference value for tightening torque, [Nm]
clamp length, between the nut bearing surface and bolt bearing surface, [mm]
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Assembly method
Reference: EN 1090-2, § 8.2: Use of bolting assemblies.
Bolts and nuts shall not be welded, unless otherwise specified.
Preloaded assemblies do not need additional locking device, unless otherwise specified.
5.1
Bolts
The nominal fastener diameter used for structural bolting shall be at least M12.
The bolt length shall be chosen to such that after tightening the length of bolt end protrusion
shall be at least the length of one thread pitch measured from the outer face of the nut to the
end of the bolt.
Clamp lengths () shall be in accordance with those specified in table A.1 of EN 14399-4,
attached to this document.
5.2
Nuts
Nuts shall run freely on their partnering bolt, which is easily checked during hand assembly.
Any nut and bolt assembly where the nut does not run freely shall be discarded.
If a power tool is used, either of the following two checks may be used:
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•
for each new batch of nuts or bolts their compatibility may be checked by hand
assembly before installation;
for mounted bolt assemblies but prior to tightening, sample nuts may be checked for
free-running by hand after initial loosening.
Nuts shall be assembled so that their designation markings are visible for inspection after
assembly.
5.3 Washers
Washers shall be used under both the bolt head and the nut.
For preloaded bolts, used washer shall be chamfered according to EN 14399-6.
Washer used under head shall be positioned with the chamfer towards the bolt head.
Washer used under nuts shall be positioned with the chamfer towards the nut.
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Tightening of preloaded bolts: HV system.
References:
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EN 1993-1-8, § 3.4: Categories of bolted connections.
EN 1090-2, § 8.5: Tightening of preloaded bolts.
Requirements concerning tightening parameters for system HV, classes K1 and K0, are
described hereafter.
6.1
Nominal minimum preloading force
Unless otherwise specified, the nominal minimum preloading force, , shall be taken as:
In the case when a lower level of preload is specified, the bolt assemblies, the tightening
method, the tightening parameters and the inspection requirements shall also be specified.
6.2
Tightening method, class K1
Assemblies according to HV system, class K1, combined tightening method
(initial torque + angle) is required.
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Combined method (initial torque + angle)
Tightening by the combined method comprises two steps: first applying a specified initial
torque, and then applying a proper rotation to the turned part of the assembly:
1 - Initial torque
to tighten, using a torque wrench offering a suitable range (capable of an accuracy of
± 4%, according to EN ISO 6789), up to a value of the initial torque of about
This first step shall be completed for all bolts in one connections before starting the
second step.
The torque reference values, to be used for a nominal minimum preloading force, ,
based on k-class K1 declared by Agrati, according to the standards EN 14399, are
determined using this equation:
with = factor included in the prescribed limits for k-class K1 (0,10 0,16).
For simplification, unless otherwise specified, this value of could be considered:
The values of nominal minimum preloading force, , and reference value for the
initial tightening torque, , are shown in Table 1.
1
Thread
M12
M16
M20
M22
M24
M27
M30
M36
2
3
Nominal minimum
Initial tightening torque,
preloading force,
[Nm], for = 0,13
[kN]
59
69
110
171
172
334
212
455
247
578
321
846
393
1149
572
2007
Table 1: combined method. Initial tightening torque values.
2 - angle
to rotate the turned part of the assembly (the nut, excluding exceptions that require
special precautions) of an angle specified in Table 2. The final rotation of the nut
relative to the bolt thread shall be easily determined at the end of the tightening,
using, for example, a marking crayon or a marking paint.
Clamp length
d = nominal thread diameter
Further rotation to be applied, during the
second step of tightening
Degrees
Part turn
< 2d
60
1/6
2d < 6d
90
1/4
6d < 10d
90
1/4
NOTE: where the surface under bolt head or nut is not perpendicular to the bolt axis, the
required angle should be determined by testing.
Table 2: Combined method. Further rotation.
Note
For the family of clamping lengths 6d < 10d , the rotation angle, shown in table 2,
has been reduced compared to the value recommended by EN 1090-2.
This new definition, permitted by EN 1090-2 (§ 8.5.4), allows an additional safety
margin against the failure of the joint, while ensuring the minimum nominal preload
required by the harmonized standards.
(An alternative method for the calibration of high strength structural bolting assembly for
preloading is indicated in the Annex H of the standard EN 1090-2:2008.)
6.3
Tightening method, class K0
Several methods of tightening, subjected to the utilization of appropriate systems of
measurement (direct or indirect) of the preload, could be used.
Minimum preload values are shown in table 1, column 2.
Tightening methods (procedures and measuring system) should be defined and developed
every time.
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Inspections and testing of preloading bolted connections
Reference: EN 1090-2, chapter 12.5.2: Inspection and testing of preloaded bolted connections.
7.1 Before tightening
All connections with preloaded mechanical fasteners shall be visually checked after they are
initially bolted up with the structure aligned locally and before starting the preloading.
If chamfered washers are installed, they shall be visually checked to ensure that, during
assembly, their positioning is correct (ref. §5.3 of this document).
The torque wrench used in the first step of the combined method shall be correctly
calibrated: the tool calibration certification shall be checked yearly and its accuracy shall be
±4%, according to EN ISO 6789.
7.2 During and after tightening
General requirements for the inspection of the correct tightening of the assemblies:
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inspection of installed fasteners and/or method of installation shall be undertaken
depending on the tightening method used. The location selected shall be on a random
basis ensuring that the sampling covers the following variables as appropriate:
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connection type;
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bolt group;
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fastener lot;
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components type and size;
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equipment used;
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operatives.
for the purposes of the inspection, a "bolt group" is defined as bolt assemblies of the
same origin, in similar connections, with the bolt assemblies of the same size and class.
A large bolt group may be subdivided into a number of subgroups for inspection
purposes.
the pre-tightening step shall be checked by visual inspection of connection to ensure
they are fully packed. Under-tightening conditions shall also be checked.
for final tightening inspection, the same bolt assembly shall be used for checking both
under-tightening and, if specified, over-tightening.
if the inspection leads to a rejection, all the bolting assemblies in the bolt subgroup shall
be checked and corrective actions shall be taken.
If fasteners are not applied in accordance with the method defined in standard EN 1090-2
and by Agrati, the removal and the replacement of the whole bolt group shall be witnessed.
The criteria that define the non-compliance and the corrective actions that shall be taken in
case of tightening by combined method are specified below.
7.2.1
Inspection of tightening by the combined method
Both steps of combined method (torque and angle) shall be checked during the assembling
on the structure.
If the connections are not fully packed, the calibrations of the torque wrenches in
combination with the applied loads shall be controlled by supplementary test to achieve the
correct initial pre-tightening load. If necessary, the first step has to be repeated with the
corrected torque values.
Before starting the second step, the marking of all the nuts relative to the bolts threads shall
be visually inspected. Any mark missing shall be corrected.
After the second step, the marks shall be inspected with the following requirements:
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if the rotation angle is more than 15° below the specified value, this angle shall be
corrected;
if the rotation angle is more than 30° over the specified angle, or the bolt or the nut has
failed, the bolt assembly shall be replaced by new one.
A complete overview of inspections that shall been carried out during tightening by
combined method is shown in the chapter 12.5.2.5 of the standard EN 1090-2.
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Recommendations
Functional characteristics, especially those influenced by the lubricant performance, may
change if:
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the components of the assembly are left exposed to weathering in the construction site
awaiting the mounting;
the components, during storage or transport, are subjected to surface damage or
permanent deformations.
Tightening performances defined by K1 class are guaranteed only if:
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components in compliance with EN 14399, supplied by Agrati, are used;
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all components have the same coating;
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the lubrication of bolts, nuts and washers is not modified;
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tightening is executed by the rotation of the nut;
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assembly components are tightened only one time (components shall not be re-used).
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used assemblies are drawn directly from the individual packages and all the expedient to
avoid the mixing of lots have to be carried out.
In the case of manipulation of supply conditions and non compliance with the operative
instructions, any complaints will be dismissed.
Annex A - Prescribed clamp lengths
Diameter
of thread
M12
M16
M20
M22
16-21
21-26
26-31
31-36
36-41
41-46
46-51
51-56
56-61
61-66
66-71
71-76
76-81
17-22
22-27
27-32
32-37
37-42
42-47
47-52
52-57
57-62
62-67
67-72
72-77
77-82
82-87
87-92
92-97
97-102
102-107
107-112
M27
M30
M36*
HV assemblies - Clamping length t
Nominal length l
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
150
155
160
165
170
175
180
185
190
195
200
*only on request
M24
18-23
23-28
28-33
33-38
38-43
43-48
48-53
53-58
58-63
63-68
68-73
73-78
78-83
83-88
88-93
93-98
98-103
103-108
108-113
113-118
118-123
123-128
128-133
22-27
27-32
32-37
37-42
42-47
47-52
52-57
57-62
62-67
67-72
72-77
77-82
82-87
87-92
92-97
97-102
102-107
107-112
112-117
117-122
122-127
127-132
132-137
137-142
29-34
34-39
39-44
44-49
49-54
54-59
59-64
64-69
69-74
74-79
79-84
84-89
89-94
94-99
99-104
104-109
109-114
114-119
119-124
124-129
129-134
134.139
139-144
144-149
149-154
154-159
159-164
164-169
36-41
41-46
46-51
51-56
56-61
61-66
66-71
71-76
76-81
81-86
86-91
91-96
96-101
101-106
106-111
111-116
116-121
121-126
126-131
131-136
136-141
141-146
146-151
151-156
156-161
161-166
166-171
39-44
44-49
49-54
54-59
59-64
64-69
69-74
74-79
79-84
84-89
89-94
94-99
99-104
104-109
109-114
114-119
119-124
124-129
129-134
134.139
139-144
144-149
149-154
154-159
159-164
164-169
43-48
48-53
53-58
58-63
63-68
68-73
73-78
78-83
83-88
88-93
93-98
98-103
103-108
108-113
113-118
118-123
123-128
128-133
133-138
138-143
143-148
148-153
153-158
158-163