Civil Engineering Reference
In-Depth Information
Minimum end plates length
=
(
2
/
3
)(
1.25
)(
15
)
=
12.5 in.
Minimum intermediate plates length
=
(
3
/
4
)(
12.5
)
=
9.38 in.
Minimum thickness of stay plate
0.30 in.
For 7/8 in. diameter Bolts, maximum fastener spacing
=
(
1
/
50
)(
15
)
=
=
4
(
7
/
8
)
=
3.5 in.
Minimum stay plate length
=
10 in. (minimum of three bolts per side of
the stay plate).
Thebridgedesignerwillusetheseminimumrequirementstoselectdesign
dimensions of lacing bars and stay plates.
6.3 AXIAL COMPRESSION MEMBERS
Axial compression main members in steel railway superstructures are often nonre-
dundant. Therefore, the strength (yielding and stability) limit state requires careful
consideration during design.
6.3.1 S
TRENGTH OF
A
XIAL
C
OMPRESSION
M
EMBERS
The strength of a steel compression member is contingent upon its susceptibility to
instability or buckling. For very short members, failure is governed by yield stress,
F
y
.
∗
However, for members with greater slenderness, inelastic or elastic instability,
depending on the degree of slenderness, will govern the failure at a critical buckling
force,
P
cr
.
6.3.1.1
Elastic Compression Members
Long and slender members will buckle at loads with compressive stresses below the
proportionallimit,
F
p
(Figure6.3).Themagnitudeofthiselasticcriticalbucklingforce
depends on the stiffness, length, and end conditions of the compression member; as
well as imperfections in loading and geometry.
F
U
F
Y
F
p
Stress
F
Y
F
p
Strain
FIGURE 6.3
Typical stress-strain curve for structural steel.
∗
Compressive yield stress is almost equal to tensile yield stress (see Chapter 2).
