Frequently Asked Questions

Bolting

What torque should I use to inspect installed ASTM high-strength structural bolts?
1/1/1996

In many cases, such as bearing-type joints, this type of inspection is completely unnecessary. In cases were the bolts require pretensioning, such as slip-critical, proper installation procedures (turn-of-nut) need not require inspection using a torque wrench, unless there is a dispute over the installation procedures. If the bolt installation has been completed some time previously, determining the appropriate inspection torque may not even be possible. The torque that relates to a particular tension is dependent on many factors, some of which are thread fit, condition of the threads, lubrication on the threads and on the washer face of the turned element, and the presence or absence of a washer under the turned element. Essentially inspection torque must be determined at the time the bolts in the particular joints are being installed. The reason is that one needs a bolt calibrator capable of determining bolt tensions as well as fastener assemblies (bolts, nuts and washers) of like condition (same diameter, length and thread condition) as the assemblies being inspected.

Considering that bolts may be black, galvanized or cadmium plated (A325 or A325M only), and that for galvanizing, it may be either hot-dipped or mechanical, the range on torque for a particular tension could be a factor of two. Therefore, anyone possessing a "Job Inspection Torque Table" should destroy same. The procedures for installing and inspection of joints using ASTM A325, A490, A325M and A490M bolts are given in Clause 23 of CSA Standard CAN/CSA-S16.1-94.

Studies of tensions that actually exist in bolts installed in the field by ironworkers, undertaken by the Research Council on Structural Connections (RCSC), confirm that mean tensions in excess of the specified minimum values are achieved by crews who are properly trained and exercise reasonable care in their work.

Additional information on this topic may be found in the Commentary to Clause 23 in Part Two of the CISC Handbook of Steel Construction, Sixth Edition; and "Inspection of Fastener Installation in High-Strength Bolted Joints" by Dr. G.L. Kulak, Advantage Steel, CISC, No.1, May 1993.