STRUCTURAL STEEL BOLT TIGHTENING PROCEDURE
ASTM A 325/ A 325M high strength bolts, 3/4" (20mm) in diameter shall be used in all bolted structural connections, unless otherwise noted in the contract documents. However, larger ASTM A325/ 325M bolts may be used when required to meet connection capacity requirements and shall be clearly flagged on the erection drawings.
All ASTM A325 or ASTM A325M high-strength bolts, shall be Type-1, galvanized. Galvanized washers and nuts shall be furnished for galvanized bolts. All bolts, nuts and washers shall be properly identified and marked with the material grade and manufacturer's logo if required by respective ASTM standard. All fasteners not so marked shall be rejected. Should any unmarked fasteners be installed, they shall be removed. Mechanical testing of unmarked fasteners shall not constitute justification for their use.
ASTM A 325/A325M Bolts shall not be reused.
Mechanically galvanized bolts & nuts shall not be intermixed with hot dip galvanized ones.
Snug-Tightened Joints
All bolt holes shall be aligned to permit insertion of the bolts without undue damage to the threads. Bolts shall be placed in all holes with washers positioned if required and nuts threaded to complete the assembly. Compacting the joint to the snug-tight condition shall progress systematically from the most rigid part of the joint. The snug-tightened condition is the tightness that is attained with a few impacts of an impact wrench or the full effort of an ironworker using an ordinary spud wrench to bring the connected plies into firm contact.
Pre-tensioned Joints
For pre-tensioning methods, paragraph 6.2.1 shall be used, except when alternative design fasteners or alternative washer-type indicating devices that meet the requirements are used, in which case, installation instructions provided by the manufacturer shall be followed.
Calibrated Wrench Pre-tensioning:
The pre-installation verification procedures specified in Section 5 shall be performed daily for the calibration of the installation wrench. Torque values determined from tables or from equations that claim to relate torque to pretension without verification shall not be used. All bolts shall be installed in accordance with the requirements, with washers positioned as required in drawings. Subsequently, the installation torque determined in the pre-installation verification of the fastener assembly shall be applied to all bolts in the joint, progressing systematically from the most rigid part of the joint in a manner that will minimize relaxation of previously pre-tensioned bolts. The part not turned by the wrench shall be prevented from rotating during this operation. Application of the installation torque need not produce a relative rotation between the bolt and nut that is greater than the rotation specified requirement.
