Civil Engineering Reference
In-Depth Information
1
A
g
A
bb
,
1.10
(L/r)
2
ab
r
bb
+
1
a
2
2
r
2
α =
+ Ω
P
cr
=
+
(6.49b)
where
a
isthedistancebetweenthecentroidsofbattenplates,
b
isthedistancebetween
the centroids of the main compression elements of the member (effective batten plate
length),
I
bb
isthemomentofinertiaofthebattenplate
=
t
bb
(w
bb
)
3
/
12,
t
bb
isthebatten
plate thickness,
w
bb
is the b
atten pl
ate width,
A
bb
is the batten plate cross-sectional
area
t
bb
w
bb
, and
r
bb
=
√
I
bb
/A
bb
.
If the shear rigidity of the batten plates is small, reduction of the built-up compres-
sion member critical buckling force will result. Inclusion of the batten plate shearing
strain into Equation 6.49a yields
=
a
2
24
E
eff
I
+
ab
12
E
eff
I
bb
+
a
A
bb
G
eff
b
β
Ω =
(6.49c)
1
A
g
A
bb
ab
r
bb
+
. (6.49d)
1.10
(L/r)
2
1
a
2
2
r
2
31.2
a
b
α =
+ Ω
P
cr
=
+
+
6.3.3.1.3 Critical Buckling Strength of Laced Bar Built-up Compression
Members with Batten Plates (Pinned at Each End)
∗
(Figure 6.13d
and e)
Shear is resisted by pin-connected truss behavior of lacing bars (for double lacing,
consider tension resistance only).
1
A
lb
E
eff
sin
b
A
bb
E
eff
a
,
Ω =
φ
+
(6.50a)
cos
2
φ
1
α =
+ Ω
P
cr
13.2
(L/r)
2
A
A
lb
A
g
A
bb
1
tan
.
1
=
1
+
+
(6.50b)
cos
2
sin
φ
φ
φ
6.3.3.1.4 Critical Buckling Strength of Built-up Compression Members
with Perforated Cover Plates (Pinned at Each End)
(
Figure 6.13f)
Most built-up compression members in modern steel railway superstructures are com-
prised of main elements connected by perforated cover plates. Shear is resisted by
flexure of the main member elements because the perforated cover plates act as rigid
∗
This equation was developed and then later used by Engesser in connection with investigations into
the collapse of the Quebec Bridge (see Chapter 1).
