Civil Engineering Reference
In-Depth Information
TABLE 6.7
Minimum Lacing Bar Thickness
Member
t
lbmin
Single Lacing
t
lbmin
Double Lacing
Main
L
lb
/
40
L
lb
/
60
Bracing
L
lb
/
50
L
lb
/
75
lacing systems
(
Figure 6.13b and e)
(equivale
nt leng
th of the lacing bar between
connections at the main member), and
r
lb
=
√
I
lb
/A
lb
=
0.29
t
lb
for flat lacing bars.
Double lacing systems are used to reduce lacing bar slenderness and thickness. In
particular, AREMA (2008) recommends that double lacing connected at the center
be used when
b >
15 in. and the lacing bar width is less than 3.5 in.
The minimum thickness of lacing bars based on the slenderness recommenda-
tions of AREMA (2008) is indicated in Table 6.7. In order to ensure adequate edge
distance for connections and accommodate theAREMA (2008) recommendation that
the lacing bar connection bolt diameter does not exceed 1/3 of the lacing bar width,
w
lb
/
3, the minimum lacing bar width should be 2
8
in. for 7/8 in. diameter bolts.
6.3.3.1.6.2 Stay Plates for Built-up Compression Members
Stay plates must
be used at the ends of laced bar built-up compression members and at locations where
the lacing bars are interrupted (e.g., at a connection with another member).
The length of the stay plates at the ends of laced bar built-up compression mem-
bers must be at least 25% greater than the distance between connection lines across
the member (distance
b
in
Figure 6.13)
.
The length of the stay plates at intermediate
locations of laced bar built-up compression members must be at least 75% of the dis-
tance between connection lines across the member. The minimum thickness of the
stay plate,
t
sp
, as recommended by AREMA (2008) is shown in Table 6.8.
The center-to-center spacing of bolts must not exceed four bolt diameters and not
less than three bolts should be used to connect stay plates to main elements of the
built-up compression member. Welded stay plates shall utilize a minimum 5/16 in.
continuous fillet weld along the stay plate longitudinal edges.
Example 6.7 outlines the design of a laced built-up compression member.
TABLE 6.8
Minimum Stay Plate Thickness
Member
Minimum Stay Plate Thickness (
t
sp
)
Main
b/
50
Bracing
b/
60
