Civil Engineering Reference
In-Depth Information
The bending stress in each main member element from shear forces applied on each
side of the member is then calculated to ensure that it does not exceed 0.55
F
y
.
∗
Also, when batten plates are used without lacing bars, the batten plate spacing,
a
, is critical in regard to the overall stability of the built-up compression member, as
indicated by Equations 6.49b and 6.49d.
The minimum thickness recommended in
Table 6.8
for stay plates for main and
bracing members also appears appropriate for batten plates. Also, if used, the min-
imum width and connection geometry of batten plates should consider the criteria
outlined for stay plates.
Example 6.7 outlines the design of a batten plate built-up compression member.
6.3.3.1.6.4 Perforated Cover Plates for Compression Members
In order to
avoid the fabrication cost of laced bar built-up compression members and the bending
inefficiencies of using batten plates, perforated cover plates are often used for built-up
compression members in modern railway steel superstructures.
AREMA (2008) recommends, to ensure stability of the main member elements
at perforations, that the effective slenderness ratio,
C
pc
, about the member axis
(Figure 6.15)
not exceed 20 or 33% of the member slenderness ratio about an axis
perpendicular to the plane of the perforation. The effective slenderness ratio is
c
r
pc
≤
L
3
r
,
C
pc
=
20
≤
(6.69)
where
c
is the length of the perforation, and
I
pc
A
pc
r
pc
=
,
A
1
x
'
A
pc
=2(
A
1
) +
A
2
I
pc
=2(
I
y1
) +
I
y2
+
A
pc
(
x
')
2
A
2
I
pc
r
pc
=
A
pc
c
r
pc
C
pc
=
FIGURE 6.15
Element of compression member at a perforation.
∗
The main member elements between batten plates can be considered as flexural compression members
with
L/r
=
0 (Tall, 1974).
