4. Two identical steel plates are each 1 in thick, and are compressed with one bolt (1/4-20 UNC grade 8) and nut. Washers are used under the head of the bolt and under the nut.

a) Determine a suitable length of the bolt, rounded up to the nearest 1/4"

b) Determine the bolt stiffness, assuming E = 30x10^6.

c) Determine the stress on the bolt if the preload is 3 kip, and service load is 15 kip, and material stiffness is 12.69 Mlbf/in.