Steel Bearing Plate thickness design LRFD

[jsburk0]

I am working on a micropile underpinning design and need some help with the bearing plate design I have a micropile with a compressive load of 30 kips. The connection of a gusset plate will be on the exterior of the foundation, secured with 18, 1/2" bolts. I need to check the punching shear of the bearing plate thickness relative to the securing nut below. I have researched punching shear of steel plates and found an AISC LRFD formula (attached). I understand the basics, but need to understand where all the reduction factors are coming from. Mainly the 0.6 factors. From what I've found, the 0.75 associated with the ultimate shear strength is related to the resistance factor of a member in tension? If someone has a better way or could point me to a correct formula, I would appreciate the help.

Thanks

Joe