1 1/4" Dia. A490 Bolts in oversized holes
Solutions:
When using 1 1/4" diameter A490 bolts in oversized holes, because the 5/16" thick F436 flat washers may have an ID that exceeds the maximum allowed on one of its faces, it may not be possible to verify that the intended DTI/bolt/flat washer assembly functions correctly in the Installation Verification Procedure (see FAQ Inspection Procedure) required by the Research Council on Structural Connections. Because the F436 flat washer often has a very large ID on one side, (check the ID tolerance against ASTM F436) its orientation MAY have an influence on the apparent compression performance of the DTI. This situation has recently been noted when the DTI was to be used on the nut end of the bolt. If this situation is encountered, either the orientation of the 5/16" F436 flat washers must be monitored so that the small ID side is against the underside of the DTI, or the DTI must be used under the bolt head, or both.
Explanation:
Both the Research Council Specification and Applied Bolting's "DTI Installation and Inspection" instructions call for a field verification test of the bolts, nuts, flat washers, and DTI's to be done prior to bolting being done on the site. This test must verify that some assembly combination and inspection procedure is available which is capable of demonstrating that the minimum allowable bolt preload plus 5% (84,000 lb. for 1 1/8" A490 bolts, and 106,000 lb. for 1 1/4" A490 bolts) can be obtained. The Research Council further notes that " ... Special attantion shall be given to proper installation of flat hardened washers when Direct Tension Indicating devices are used with bolts installed in oversized or slotted holes and when the load indicating devices are used under the turned element .. "
The combination of oversized holes in the steelwork, 5/16" thick ASTM F436 flat washers that have a very large ID on one face (see sketch below), and DTI's, together MAY make it difficult to allow any random combination of flat washers and DTI washers on all bolts. The 5/16" thick flat washers which themselves have too large an ID MAY prove insufficient support for the Direct Tension Indicators to function so that their compression can be judged in the normal manner by using a feeler guage.
The Installation Verification Procedure should be attempted as follows:
- Three bolt assemblies with 5/16" flat washers and a DTI in the intended orientation should be assembled in a Skidmore-Wilhelm device, the load taken up to 84,000 or 106,000 lb. manually or with a non-impacting wrench. The flat washers should have their SMALLEST ID bearing on the underside of the DTI, to simulate a hole of standard diameter.
- The number of entries of a .005" or .015" feeler guage should be noted, with a minimum of ONE.
- The inspection procedure in the steelwork should then be based on some MAXIMUM number of entries of the same feeler gage as that found in #2 above. Zero entries, that is when the DTI appears to be "flat", is an acceptable installation and inspection procedure.
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