2.3 Staggered holes

Failure due to staggered holes

When a member has staggered bolt holes, a different approach to finding $A_e$ for the fracture limit state is taken. This is because the effective net area ( $t$ x $w_n$ ) is different as the line of fracture changes due to the stagger in the holes. The test for the yielding limit state remainsunchanged (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 memberwith 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, $w_n$ .

Net width

In order to find the net width, first the variables $s$ and $g$ must be known. They are shown in .

Where:

• $w_n$ = net width
• $w_g$ = gross width
• ${\phi }_d={\phi }_b+\frac{1}{16}+\frac{1}{16}$ where: ${\phi }_b$ = diameter of the bolt
• $N$ = number of bolts in cross section
• $s$ = longitudinal center-to-center spacing of any two consecutive holes, in.
• $g$ = transverse center-to-center spacing between fastener gage lines, in.
• The term $\frac{s^2}{4g}$ is added for every non-straight segment