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|
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.