Page 27 - Handbook of Structural Steel Connection Design and Details

Fasteners and Welds for Structural Connections

12 Chapter One

that would prevent solid seating of the parts, especially dirt, burrs, and
other foreign material. Contact surfaces within slip-critical joints should
be free of oil, paint (except for qualified paints), lacquer, and rust inhibitor.
High-strength bolts usually are tightened with an impact or TC
wrench. Only where clearance does not permit its use will bolts be hand-
tightened
Each high-strength bolt should be tightened so that when all fasten-
ers in the connection are tight it will have the total tension (kips) for its
diameter. Tightening should be done by one of the following methods,
as given in the RCSC specifications (2004).

Calibrated-wrench method. When a calibrated wrench is used, it must
be set to cut off tightening when the required tension has been exceeded
by 5 percent. The wrench should be tested periodically (at least daily on
a minimum of three bolts of each diameter being used). For this purpose,
a calibrating device that gives the bolt tension directly should be used.
In particular, the wrench should be calibrated when bolt size or length
of air hose is changed. When bolts are tightened, bolts previously ten-
sioned may become loose because of compression of the connected parts.
The calibrated wrench should be reapplied to bolts previously tight-
ened to ensure that all bolts are tensioned to the prescribed values.

Turn-of-the-nut method. When the turn-of-the-nut method is used, tight-
ening may be done by impact or hand wrench. This method involves the
following three steps:

1. Fit up of connection. Enough bolts are tightened a sufficient amount
to bring contact surfaces together. This can be done with fit-up bolts,
but it is more economical to use some of the final high-strength bolts.
2. Snug tightening of bolts. All high-strength bolts are inserted and
made snug-tight (tightness obtained with a few impacts of an impact
wrench or the full effort of a person using an ordinary spud wrench).
While the definition of snug-tight is rather indefinite, the condition
can be observed or learned with a tension-testing device.
3. Nut rotation from snug-tight position. All bolts are tightened by the
amount of nut rotation specified in Table 1.7. If required by bolt-
entering and wrench-operation clearances, tightening, including by
the calibrated-wrench method, may be done by turning the bolt while
the nut is prevented from rotating.

Direct tension indicator. The direct tension indicator (DTI) hardened-
steel load-indicator washer has dimples on the surface of one face of
the washer. When the bolt is tensioned, the dimples depress to the

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