Pad and Pier with Rock anchors

[bonbon83]

Hi All! I have 3 questions regarding a pad and pier that is going to handle shear, upload and download Force. The pad is on the rock and I am going to use 4 rock anchors at the corners to help me with upload capacity. I have seen it is common practice that designers apply prestressing force on the anchors. First question is that 1) what is the optimum prestressing force for the anchors (lockoff force)?If i take the prestressing force in the anchors equal to the anchor design load, then under ultimate factored loads,2) what would be the force in the anchors? ( i guess we use this force to size anchor?) The reason I am asking is that the ultimate factored load on anchor would be bigger than the prestressing force and if I also consider shear acting simultaneously along with uplift, then I need to consider combined tension and shear equation for the anchor capacity(no shear dowel) 3) can I rely on the anchor shear capacity? I have seen similar design with shear dowels! It seems some designer don’t consider shear capacity from the anchors and put shear dowels! Thanks All!