Civil Engineering Reference
In-Depth Information
6.3.3.1.6 Design of Lacing Bars, Stay Plates, Batten Plates, and
Perforated Plates
AREMA (2008) recommends that lacing bars, batten plates, and perforated plates be
designed for a total shear force normal to the member in the plane of the lacing bars,
batten plates, or cover plates comprised of self-weight, wind, and 2.5% of the axial
compressive force in the member.The shear forces related to self-weight and wind are
generally small and may be neglected in many cases. The shear force normal to the
member in the plane of the lacing bars, batten plates, or cover plates related to the axial
compressive force can be estimated by considering the conditions of
Figure 6.5c.
The
solution of the differential equation of the deflection curve (Equation 6.14), where
U
=
Pe
, is (Bowles, 1980)
e
tan
k
2
L
2
1
.
sin
k
2
y(x)
cos
k
2
y(x)
y(x)
=
+
−
(6.55)
Differentiating Equation 6.55 yields
k
2
e
tan
k
2
L
2
d
y(x)
d
x
=
(6.56)
and substitution of Equation 6.56 into Equation 6.40 yields
Pk
2
e
tan
k
2
L
2
V
=
.
(6.57)
AREMA (2008) recommends
k
2
e
tan
k
2
L
2
=
0.025
(6.58)
so that
V
=
0.025
P
,
(6.59)
where
A
r
F
y
150
≥
PF
y
150
F
all
V
≥
(6.60)
and
A
r
=
P/F
all
.
Equation 6.60 was developed considering force eccentricity, initial curvature, and
flexure of the compression member (Hardesty, 1935).
Figure 6.14
illustrates that the
AREMA (2008) recommendation for minimum shear force (Equation 6.60) ensures
that shear forces with relatively greater proportion to the axial compressive force are
used for the design of weaker compression members (more slender members that
approach the Euler buckling behavior) when
F
all
/F
y
<
0.26.
The shear force,
V
, forms the basis of the lacing bar, batten plate, and perforated
cover plate design for built-up compression members.
