Selecting the bolt length for any given grip and bolt diameter can be facilitated by using the chart entitled “Bolt Lengths for Various Grips” on page 6-167 in the Handbook of Steel Construction, 11th edition. The chart is applicable to the Imperial Series of ASTM F3125/F3125M bolts, such as Grades A325 and A490 high-strength bolts in bearing-type and slip-critical connections. The bolt lengths provided, however, do not necessarily result in the exclusion of bolt threads from the shear plane(s), which is a future Blog topic. The example below will illustrate the use of the Handbook chart.
Determine the bolt length for 7/8-in. F3125/F3125M grade A325 bolts and a 10 mm-thick shear tab supporting a wide-flange beam with web thickness, w = 9.7 mm.
As shown on Figure 1, the grip, by definition, is the thickness of material to be connected when washers are not used.
The grip is therefore: 10 + 9.7 = 19.7 mm. From the chart (see Figure 2), the required bolt length is 2 inches. Note that bolt lengths must be specified in inches.
If ASTM F436 flat washers are used, add 4 mm (5/32 inch) to the grip value in this Chart for each washer, as shown on Figure 3.