Torque Calculations

Torque charts and Anchor Bolts


Do Torque charts for tensioning fasteners apply to anchor bolts?


The AISC Steel Construction Manual, 13th Edition has this to say about anchor rod nut installation.

“The majority of anchorage applications in buildings do not require special anchor rod nut installation procedures or pretension in the anchor rod. The anchor rod nuts should be “drawn down tight” as columns and bases are erected. This condition can be achieved by following the same practices as recommended for snug-tightened installation in steel-to-steel bolted joints in the RCSC Specification. That is, most anchor rod nuts can be installed using the full effort of an ironworker with an ordinary spud wrench. When, in the judgment of the owner’s designated representative for design, the performance of the structure will be compromised by excessive elongation of the anchor rods under tensile loads, pretension may be required. Some examples of applications that may require pretension include structures that cantilever from concrete foundations, moment-resisting column bases with significant tensile forces in the anchor rods, or where load reversal might result in the progressive loosening of the nuts on the anchor rods. When pretensioning of anchor rods is specified, care must be taken in the design of the column base and the embedment of the anchor rod. The shaft of the anchor rod must be free of bond to the encasing concrete so that the rod is free to elongate as it is pretensioned. Also, loss of pretension due to creep in the concrete must be taken into account. Although the design of pretensioned anchorage devices is beyond the scope of this manual, it should be noted that pretension should not be specified for anchorage devices that have not been properly designed and configured to be pretensioned.” 

So, what does this all mean?

It means that in normal circumstances, the normal effort of an ironworker with a regular spud wrench is sufficient to tighten the nuts on anchor bolts. In the event that special pretensioning is required, the design engineer should have carefully designed the anchor assembly specifically for that purpose and there should be detailed instructions so that the pretensioning is carried out correctly.



The starting point for tightening procedures is between 20 and 30% of the final tension. For anchor rods this is defined as a function of torque as:


Tv = 0.12 dbTm



Tv = verification torque, in. -kips

db = nominal body diameter of the anchor rod, in.

Tm = minimum installation pretension, kips, given in Tabel A1

Till and Lefke (1994) has shown that a multiplier of 0.12 in this relationship is sufficient for common sizes and coatings of anchor rods. Other researchers have suggested a value of 0.2 for less-well-lubricated rods. If an anchor rod has a nut-head or the head is fastened with nuts, the nut should be prevented from turning while the anchor rod is tightened; this can be achieved with a jam nut or another type of locking device. The jam nut will affect the ultimate or fatigue strength of the rod. Very large torques may be necessary to properly tighten anchor rods greater than 1 inch in diameter. A slugging wrench or hydraulic torque wrench is required for the leveling nuts; an open end slugging wrench may be used.

Information from AISC Design Guide 


This is just for information purposes please consult your engineer before making any final decisions .