Civil Engineering Reference
In-Depth Information
6.3.3.1.6.3 Batten Plates for Compression Members
Built-up compression
way superstructure compression elements due to strength and stability requirements.
When batten plates are used in conjunction with laced bar compression members
(Figure 6.13d and e), they may be designed for minimum slenderness considerations
since the lacing bars are assumed to resist the applied shear forces.
However, if used without lacing bars, the spacing of batten plates,
a
, along the
main member must also be designed to preclude the buckling of portions of main
member elements between the batten plate connections. Based on theAREMA (2008)
recommendation for lacing bar spacing (Equation 6.62), it appears reasonable that
the batten plate spacing be such that
a
bp
r
p
≤
2
L
3
r
,
40
≤
(6.64)
where
a
bp
=
2
e
bp
, where
e
bp
is the edge distance to first fastener in the
batten plate and
w
bp
is the width of the batten plate.
Furthermore, when batten plates are used without lacing bars, the batten plates and
main member elements
†
on each side of the main member must be designed to resist
bending created by the shear force
V
/2 in each panel between batten plates.
The force creating bending in each batten plate,
P
bp
,is
a
−
w
bp
+
a
b
1
2
V
2
Va
4
b
.
P
bp
=
=
(6.65)
Therefore, the bending moment,
M
bp
, in each batten plate is
P
bp
b
2
Va
8
M
bp
=
=
(6.66)
such that, based on an allowable stress of 0.55
F
y
, the minimum thickness of batten
plate,
t
bp
,is
1.36
Va
F
y
(w
bp
)
2
≥
Pa
29.3
F
y
(w
bp
)
2
,
t
bp
≥
(6.67)
where
P
is the compressive force
=
fA
g
, and
f
is the calculated compressive stress in
the member.
The bending moment in the main member element,
M
p
,is
a
2
1
2
V
2
Va
8
.
M
p
=
=
(6.68)
∗
For this reason AREMA (2008) does not contain any specific recommendations relating to the use of
batten plates.
†
Thiscriterionformainmemberelementswillusuallygovernthedesignofbuilt-upcompressionmembers
using only batten plates.
