The bolts shall be tightened using a torque wrench offering a suitable operating range. Hand or power operated wrenches may be used. Impact wrenches may be used for the first step of tightening for each bolt.
a) first tightening step: the wrench shall be set to a torque value of about 0.75 Mr, i with Mr, i = Mr, 2 or Mr, test. This first step shall be completed for
all bolts in one connection prior to commencement of the second step.
b) a second tightening step: the wrench shall be set to a torque value of 1.10 Mr, i with
Mr, i = Mr, 2 or Mr, test.
| Diameter | Preload [kN] | Torque 1.1 Mr,i [Nm] | Km |
|---|---|---|---|
| M12 | 59 | 100 | 0.129 |
| M16 | 110 | 250 | 0.129 |
| M20 | 172 | 450 | 0.119 |
| M22 | 212 | 650 | 0.127 |
| M24 | 247 | 800 | 0.123 |
| M27 | 321 | 1250 | 0.131 |
| M30 | 393 | 1650 | 0.127 |
| M36 | 572 | 2800 | 0.124 |
Tightening torque Mr (=1.10 Mr, i) has to be applied using calibrated torque wrenches with accuracy of ± 4% According to EN ISO 6789 by rotation of the nut; different tightening procedures have to be approved by experimental tightening tests under site conditions as specified in annex H of European Standard EN 1090-2: 2008+A1:2011.