Direct Answer
The four AISC/RCSC-approved methods for high-strength bolt pretensioning are: Turn-of-Nut (torquing to a specified rotation past snug-tight), Calibrated Wrench (torquing to a specified torque value calibrated to the lot), Direct Tension Indicator (DTI washers with protrusions that flatten at the required tension), and Twist-Off (TC bolts with a splined end that shears off at the required tension).
Full Explanation
Turn-of-Nut is the oldest and most reliable method but requires careful snug-tight determination and rotation measurement. Calibrated Wrench is convenient but must be calibrated daily or per bolt lot. DTI washers provide a visual proof of pretension and are popular for inspection. TC bolts (Tension Control) are the fastest method — the installer simply drives until the spline shears, providing a definitive visual indicator of pretension. The RCSC Specification for Structural Joints (RCSC) governs all four methods.
What This Means for Your Shop
If your project requires pretensioned or slip-critical connections, select your installation method at project start and procure the appropriate equipment. TC bolt installation is fastest but requires TC wrenches; the special inspector must observe and document installation.
Common Mistakes
Using an impact gun on pretensioned bolts without calibrating to the required torque. An uncalibrated impact gun may achieve less than the required pretension, creating an uninspected structural deficiency.
Recommended Process
Before beginning pretensioned bolt installation, conduct a pre-installation verification: test bolts from the same lot in a skidmore device or torque meter to confirm the installation method produces required pretension at the site conditions. Document the results.