High strength structural bolting assemblies for preloading, according to EN 14399.

Technical information for use. Contents 1. Scope

2. Normative References

3. General

4. Symbols and units

5. Assembly method

5.1 Bolts 5.2 Nuts 5.3 Washers

6. Tightening of preloaded bolts: HV system.

6.1 Nominal minimum preloading force 6.2 Tightening method, class K1 6.3 Tightening method, class K0

7. Inspection and testing of preloaded bolted connections

7.1 Before tightening 7.2 During and after tightening

7.2.1 Inspection of tightening by the combined method

8. Recommendations

Annex A - Prescribed clamp lengths

1. 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. 2. Normative References

- 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".

3. 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: - the compliance of the assemblies bolt/nut/washers with the harmonized European standards for metallic

constructions; - the execution of a structured, controlled and certificated, by a notified external body, production

process; - 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: - a bolt, in compliance with the standard EN 14399-4; - a properly lubricated nut, in compliance with the standard EN 14399-4; - two washers, in compliance with the standards EN 14399-6; - possible direct or indirect measurement of bolt preload device. Agrati supplies assemblies in these two versions: - hot dip galvanized; - 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.

4. Symbols and units

References: EN 1993-1-8; EN 14399-2. �� nominal stress area of the bolts, [mm2]

� 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]

Σt clamp length, between the nut bearing surface and bolt bearing surface, [mm]

5. 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 (Σt ) 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:

- 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.

6. Tightening of preloaded bolts: HV system.

References: - 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:

��,� � 0,7 · ��� · ��

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. - 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

0,75 · �,

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:

�, � 0,13 · � · ��,�

The values of nominal minimum preloading force, ��,�, and reference value for the initial tightening torque, �,, are shown in Table 1.

1 2 3

Thread

Nominal minimum

preloading force, ��,� [kN]

Initial tightening torque,

0,75 · �, [Nm], for �� = 0,13

M12 59 69 M16 110 171 M20 172 334 M22 212 455 M24 247 578 M27 321 846 M30 393 1149 M36 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 Σt

d = nominal thread diameter

Further rotation to be applied, during the second step of tightening

Degrees Part turn Σt < 2d 60 1/6

2d ≤ Σt < 6d 90 1/4 6d ≤ Σt < 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 ≤ Σt < 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.

7. 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:

a) 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:

- connection type; - bolt group; - fastener lot; - components type and size; - equipment used; - operatives.

b) 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.

c) 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.

d) for final tightening inspection, the same bolt assembly shall be used for checking both under-tightening and, if specified, over-tightening.

e) 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:

a) if the rotation angle is more than 15° below the specified value, this angle shall be corrected; b) 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. 8. Recommendations

Functional characteristics, especially those influenced by the lubricant performance, may change if: - 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: - components in compliance with EN 14399, supplied by Agrati, are used; - all components have the same coating; - the lubrication of bolts, nuts and washers is not modified; - tightening is executed by the rotation of the nut; - assembly components are tightened only one time (components shall not be re-used). - 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 M24 M27 M30 M36*

Nominal length l HV assemblies - Clamping length Σt

35 16-21

40 21-26 17-22

45 26-31 22-27 18-23

50 31-36 27-32 23-28 22-27

55 36-41 32-37 28-33 27-32

60 41-46 37-42 33-38 32-37 29-34

65 46-51 42-47 38-43 37-42 34-39

70 51-56 47-52 43-48 42-47 39-44 36-41

75 56-61 52-57 48-53 47-52 44-49 41-46 39-44

80 61-66 57-62 53-58 52-57 49-54 46-51 44-49

85 66-71 62-67 58-63 57-62 54-59 51-56 49-54 43-48

90 71-76 67-72 63-68 62-67 59-64 56-61 54-59 48-53

95 76-81 72-77 68-73 67-72 64-69 61-66 59-64 53-58

100

77-82 73-78 72-77 69-74 66-71 64-69 58-63

105 82-87 78-83 77-82 74-79 71-76 69-74 63-68

110 87-92 83-88 82-87 79-84 76-81 74-79 68-73

115 92-97 88-93 87-92 84-89 81-86 79-84 73-78

120 97-102 93-98 92-97 89-94 86-91 84-89 78-83

125 102-107 98-103 97-102 94-99 91-96 89-94 83-88

130 107-112 103-108 102-107 99-104 96-101 94-99 88-93

135

108-113 107-112 104-109 101-106 99-104 93-98

140 113-118 112-117 109-114 106-111 104-109 98-103

145 118-123 117-122 114-119 111-116 109-114 103-108

150 123-128 122-127 119-124 116-121 114-119 108-113

155 128-133 127-132 124-129 121-126 119-124 113-118

160

132-137 129-134 126-131 124-129 118-123

165 137-142 134.139 131-136 129-134 123-128

170

139-144 136-141 134.139 128-133

175 144-149 141-146 139-144 133-138

180 149-154 146-151 144-149 138-143

185 154-159 151-156 149-154 143-148

190 159-164 156-161 154-159 148-153

195 164-169 161-166 159-164 153-158

200 166-171 164-169 158-163

*only on request