Standard DTI FAQs
When DTI's are used, should the bolts be inspected using a torque wrench?
No, definitely not. Because the torque resistance of the bolt assembly does not give a suitably accurate indication of bolt tension. The Research Council on Structural Connections states that the inspector's responsibilityis to ensure that the bolting demonstration testing and actual installation is according to the approved project procedure. In the case of bolts installed with DTI's, this means that the inspector must make sure that a snug pass is done, and then that the DTI's have been compressed sufficiently ( see feeler gage inspection criteria, properly compress DTI bumps, completely flattened DTI's). The Council goes on to say that use of the "delayed verification procedure" involving the establishment and application of a "job inspecting torque" using a torque wrench "... will produce results of questionable accuracy..."
Ultrasonic bolt tension tests on thousands of bolts tightened with DTI's verifies that when the joint has been properly compacted during the snug pass (that is by partial but not complete compression of the DTI bumps) and when the DTI's have been correctly compressed during the final pass, all or certainly the vast majority of the bolts will have tensions at or above the specified minimum (click for a chart of bolt tension).
