[TowerTalk] Base bolt depth in existing concrete

[Chris Wendling]

Vic,
  
  Check out the epoxy's at Marine Tek. I've used them, and they are very  good, especially for outdoor applications with lots of moisture.
  As far as bolt depth, go as deep as you practically can. When a bolt  pulls free from being embeded in concrete, it can pull a cone of  concrete with it. Assuming bolt diameter between 1/2 and 1",  I  would go a foot deep, because you really don't know the tensile  strength of the concrete.
  Fortunately, for tower bases, the loads are usually more shear than  tensile on the bolts.(Do NOT overtighten upon assembly.) The location  of the holes, relative to the edges of the "pad" also plays into the  equation. Err on the safe side, and drill as deep as your patience or  drill bit will allow, but I would make it at leat a foot deep in  "unknown" concrete. Rent a BIG hammer drill, and wait for a cool day.  Keep the hole clean as you drill. Also,
  epoxy embedding can actually be better than direct casting of the stud  in concrete when poured, especially in high shear/vibration loads,  which can chip away at the high stress points at the surface of the  concrete where the stud enters. The epoxy can stabilize that interface.
  
  73,
  Chris-AI4MI