Page 19 - Handbook of Structural Steel Connection Design and Details

Fasteners and Welds for Structural Connections

4 Chapter One

3. In all structures carrying cranes of more than 5-ton (50 kN) capac-
ity: roof truss splices and connections of trusses to columns, column
splices, column bracing, knee braces, and crane supports
4. Connections for the support of machinery and other live loads that
produce impact or reversal of load
Also, AISC Specification section J3.1 requires that A490 bolts subject
to tension loads be pretensioned. In all other cases, A307 bolts and snug-
tight A325 and A490 bolts can be used.
In general, the use of high-strength structural bolts shall conform to
the requirements of the Research Council on Structural Connections
(RCSC) “Specification for Structural Joints Using ASTM A325 and A490
Bolts,” 2004. This document, which is specific to A325 and A490 bolts,
contains all of the information on design, installation, inspection, washer
use, compatible nuts, etc. for these bolts. There is no comparable docu-
ment for A307 bolts. The RCSC “bolt spec.” was developed in the 1950s
to allow the replacement of rivets with bolts.
Many sizes of high-strength bolts are available, as shown in Table 1.1.
In general, a connection with a few large-diameter fasteners costs less than
one of the same capacity with many small-diameter fasteners. The fewer
the fasteners the fewer the number of holes to be formed and the less
installation work. Larger-diameter fasteners are generally favorable in con-
nections, because the load capacity of a fastener varies with the square of
7
the fastener diameter. For practical reasons, however, ⁄4- and ⁄8-in-diameter
3
fasteners are usually preferred. Shop and erection equipment is generally
set up for these sizes, and workers are familiar with them. It is also advis-
able to limit the diameter of bolts that must be pretensioned to 1 ⁄8 in since
1
this is the largest diameter tension control (TC) bolt available.
1.2.2 Washer requirements
Washers are generally not required in snug-tightened joints. However,
a beveled ASTM F436 washer should be used where the outer face of the

TABLE 1.1 Thread Lengths for High-Strength Bolts
Bolt diameter, in Nominal thread, in Vanish thread, in Total thread, in
1 1.00 0.19 1.19
1 ⁄2
5 1.25 0.22 1.47
1 ⁄8
3 1.38 0.25 1.63
1 ⁄4
7 1.50 0.28 1.78
1 ⁄8
7 1.75 0.31 2.06
1 ⁄8
1 2.00 0.34 2.34
1 ⁄8
1 2.00 0.38 2.38
1 ⁄4
3 2.25 0.44 2.69
1 ⁄8
1 2.25 0.44 2.69
1 ⁄2
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