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A325 and A490 Structural Bolts



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The AISC gives four appropriate methods to fully tension bolts for slip-critical connections. They include the "turn-of-the-nut" method (where you turn the nut through a certain number of degrees to elongate the bolt). The first edition of the AISC manual (1951) had a torque/tension table; however, the table was withdrawn in 1954 due to recognition of the tremendous variation that was found (+/-40%). "Standard" torque/tension relationships determined from tables or formulas are no longer recognized as appropriate means to control pretension. Calibrated wrench tightening may be used provided that the installation procedures are calibrated daily (for each bolt diameter, length, grade, and surface condition). The torque value is best obtained by using a calibrated torque wrench (or transducer) and a Skidmor-Wilhelm type load indicating device to equate torque to tension. The calibrated torque wrench method should be considered as the least favorable of the four tightening options.


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Atlantic Fasteners, Inc
PO BOX 19066
Greensboro, NC 27419-9066
(336) 852-0700 or (800) 233-6932 Fax: (336) 852-9730