Design of Connections for Steel Members - Design of Modern Steel Railway Bridges - page 377

TABLE 9.3
Minimum Tensile Strength of High-Strength Steel Bolts
Bolt Type F bU (ksi)

A325 with bolt diameter, d b , ≤ 1 in. 120

A325 with bolt diameter, d b , > 1 in. 105

A490 150

Bolts in connections should be installed first at the stiffest locations of the con-
nection and retightened, if required, following the installation of other bolts in the
connection (due to possible relaxation of the previously tightened bolts). A tension
measuring device should be used to measure the tension in a representative number
of bolts in the connection.

9.3.2 B OLT T YPES
Fasteners used in modern steel structures are either common or high-strength bolts.

9.3.2.1 Common Steel Bolts
Common ∗ bolts are specified by ASTM Standard A307. A307 bolts are generally
not used in applications involving live load stress reversals, cyclical stresses, and/or
vibration. A307 bolts are also not used in steel railway superstructure fabrication due
to their low strength.

9.3.2.2 High-Strength Steel Bolts

High-strength steel bolts are specified by ASTM Standards A325 and A490. The
minimum tensile strength, P bU , for A325 bolts and A490 bolts is shown in Table 9.3.
A325 Type 3 high-strength steel bolts are available in atmospheric corrosion-resistant
steel (see Chapter 2).
Equation 9.17 can be used to establish the minimum required bolt pretension, T bP ,
as shown in Table 9.4. In order to account for the threaded portion of bolts, an effective
bolt area, A st = 0.75 (A b ) , is used, such that

T bP ≥ 0.70 F bU A st ≥ 0.53 F bU A b , (9.18)

where A b is the cross-sectional area of the bolt based on nominal bolt diameter.

9.3.3 J OINT T YPES
Bolts are used in lap, “T,” corner, and butt joints. Bolted lap joints ( Figure 9.10a-d) are
often used in members of steel railway bridges. The joints in Figure 9.10b and c may

∗ Also called machine, ordinary, unfinished, or rough bolts.