Civil Engineering Reference
In-Depth Information
The prying force should be limited to a maximum of 30% of the external
load on the bolt for connections subjected to cyclical stresses in steel railway
superstructures. An allowable tensile stress range of 31.0 ksi for A325
∗
bolts is
recommended where prying forces do not exceed 30% of the external load on
the bolt.
The AREMA (2008) criteria are appropriate given the need to discourage the use
of bolted connections subject to direct cyclical tensile stress regimes in structures
such as steel railway spans.
9.3.4.2
Axially Loaded Members with Bolts in Shear
These are typically truss member end connections with forces transferred from
the axial members through connections consisting of bolts in shear and gusset plates
(Figure 9.10a)
.
Axial tension member end connections and gusset plates must be
designed considering yielding, fracture, and block shear (tear-out) failure.Axial com-
pression member end connections and gusset plates must be designed considering
buckling and block shear.
9.3.4.2.1 Axial Member End Connection
The number of bolts required in the axial force connection may be determined by
considering the allowable bolt shear stress,
f
bv
, or, if cyclically loaded, the allowable
bolt shear fatigue stress (16 or 18 ksi depending on number of design stress range
cycles).The allowable bearing stress,
f
B
, should be used for bearing-type connections.
Bearing stress may also be considered for slip-critical connections as a precaution
following slip failure. Determination of the number of bolts required to transfer forces
from the member in the connection will determine the net section area required for
the member and the basic dimensions of the connection gusset plates.
The design of axial members for strength (yield and fracture), fatigue, stability,
and serviceability is discussed in Chapter 6. The effects of the connection in terms of
net area and shear lag effects were considered in the design criteria for axial tension
members. However, the design of axial member end connections requires attention
to localized effects of bolt bearing stresses (in regard to member element thickness)
and fracture or rupture by block shear.
Axial bolted connections should conform to the recommended minimum bolt
spacing and edge distance criteria of AREMA (2008). The minimum bolt spacing
(center-to-center bolts) is three times the bolt diameter. The minimum bolt spacing,
s
b
, along a line of force, based on bearing considerations, from Equation 9.30 is
2
d
b
σ
bc
F
u
d
b
2
,
s
b
≥
+
(9.46)
where
σ
bc
is the bearing stress on connection element of area
d
b
t
p
and
t
p
is the
thickness of connection element. The recommended minimum edge distance,
e
b
,is
∗
An allowable tensile stress range of 38.0 ksi is recommended for A490 bolts.
