Standard DTI FAQs
What is meant by the term Job Inspection Gap
The RCSC (June 2000 issue, Section 8.2.4) uses the term "job inspection gap", without defining what is meant by this term. Further, the RCSC document implies that this term is found in ASTM F959, but is not.
This term means the inspection criteria to be used in the steelwork,
that is, the feeler gage thickness and number of refusals. The inspection
criteria to be used in the steelwork is determined by doing the RCSC
Pre-Installation Procedure (see How to do a site verification
test to RCSC requirements) and determining from this test whether
the DTI/Bolt combination exhibits a "useable gap" at 1.05 times the minimum
bolt preload. In the steelwork, then, the "job inspection gap" becomes
any inspection criteria that assures a residual DTI gap LESS THAN the
gap found in the RCSC pre-installation test.
For example, 1" A490 DTI's to be installed on the nut end of a bolt assembly, under a hardened flat washer, should exhibit three or four entries of a .005" feeler gage at 1.05 x 64 kips, or 67 kips in a calibrated Skidmore.
In the steelwork, then, the inspection criteria, or "job inspection gap" should be three or four REFUSALS of the same feeler gage, thus assuring a smaller gap on the DTI and therefore a (slightly) higher bolt tension.
