Civil Engineering Reference
In-Depth Information
batten plates between the perforations.
9
c
3
32
l
p
E
eff
I
,
Ω =
(6.51a)
1
3.71
(L/r)
2
c
3
l
p
r
2
,
1
α =
+ Ω
P
cr
=
+
(6.51b)
where
l
p
is the distance between the centers of perforations and
c
is the length of
the perforation. The perforation length,
c
, can be expressed in terms of the distance
between the centers of perforations,
l
p
, so that
3.71
l
p
r
2
,
3
(L/r)
2
γ
α =
1
+
(6.51c)
where
γ =
c/l
p
.
6.3.3.1.5 Design of Built-up Compression Members
The allowable compressive stress is
P
cr
FS
.
F
all
=
(6.52)
The overall critical buckling strength of the built-up compression member,
P
cr
,
(Equation 6.43) is contingent upon the main element web plates, cover plates, lac-
ing bars, and/or batten plates being of adequate strength and stability as individual
components (local buckling).
In order to ensure th
at th
e webs of main elements of built-up compression members
do not buckle prior to
P
cr
, a minimum web plate thickness,
t
w
, is recommended by
AREMA (2008) as
0.90
b
F
y
/E
√
F
all
/f
t
w
≥
(
in.
)
,
(6.53)
where
F
all
/f
4,
f
is the calculated compressive stress in the member.
Also, in order to ensure that cover
plat
es for main elements of built-up compres-
sion members do not buckle prior to
P
cr
, a minimum cover plate thickness,
t
cp
,is
recommended by AREMA (2008) as
≤
0.72
b
F
y
/E
√
F
all
/f
t
cp
≥
(
in.
)
.
(6.54)
The thickness of lacing bars, stay plates, batten plates, and perforated cover plates
must also be considered to complete the design of built-up compression members.
