Failure due to Staggered Holes
When a member has staggered bolt holes, a different approach to finding
A
e
A
e
for the fracture limit state is taken. This is because the
effective net area (tt x
w
n
w
n
) is different as the line of fracture changes due to the stagger
in the holes. The test for the yielding limit state remains
unchanged (the gross area is still the same).
Failure Lines
The net width now must account for the change in direction of the
line of fracture. First, look at different ways a tension member
with staggered holes can fracture. These pictures depict the
different lines of failure. When analyzing a member like this,
it is important to find all the lines of failure and then
determine which line of failure is the weakest cross section.
That cross section will be taken as the net width,
w
n
w
n
.
Net Width
In order to find the net width, first the variables
ss and
gg
must be known. They are shown in
Figure 2.
w
n
=
w
g
-N
φ
d
+s24g
w
n
w
g
N
φ
d
s
2
4
g
(1)
where:-
w
n
w
n
= net width
-
w
g
w
g
= gross width
-
φ
d
=
φ
b
+116+116
φ
d
φ
b
1
16
1
16
where:
φ
b
φ
b
= diameter of the bolt
-
NN = number of bolts in cross section
-
ss = longitudinal center-to-center
spacing of any two consecutive holes, in.
-
gg = transverse center-to-center
spacing between fastener gage lines, in.
-
The term
s24g
s
2
4
g
is added for every non-straight segment