Standard DTI FAQs
What do you do if the DTI's have been installed incorretly, i.e. with the bumps against the nut or with the bumps facing the steelwork?
The DTI bumps must be installed so that they are compressed by a hardened steel surface. This usually means under the bolt head with the bumps facing the bolt head, or on the nut end of the bolt with a hardened flat washer separating the turning nut from the DTI bumps (rolling bolts, one man installation). Nuts themselves are not always hardened. See Installation Instructions shown separately within this web site.
Occasionally inspectors find that the DTI has been inadvertently installed with (say) the DTI bumps bearing against the steel plates of the connection. In this situation, the apparent compression of the DTI bumps will be unreliable because the steel plates of the connection are not hardened. The correct solution is to loosen the bolt, remove the DTI and turn it around so that it is installed correctly (see Installation instructions), and retighten the bolt to the point where the DTI has been properly compressed (see FAQ). DTI's that have not been completely compressed can be reused as long as their bumps are compressed a little further.
Occasionally, with the approval of the Engineer- of- Record, DTI's are installed with the bumps facing directly against the nut, and then the bolt is tightened by turning the bolt head. Although this is not a recommended installation arrangement, it often will work correctly, especially if the nut is a hardened A563 Gr. C or Gr. DH nut or an A194 Gr. 2H nut.
If the DTI has been installed incorrectly, the first option is to remove the bolt/nut/DTI assembly, install the same hardware with the DTI positioned correctly (see rolling bolts & one man installation), and tighten the bolt properly. If this cannot be done, the fall-back procedure is to duplicate the incorrect assembly in a Skidmore-Wilhelm bolt tension calibrator, tension the bolt to the minimum installation tension (see bolt tension) plus 5%, and at that tension check that the DTI gap is LARGER than what was used in the steelwork. By inference then,in the steelwork, the bolt tension should be slightly higher (higher is good) than the minimum required (see site verification).
