[TowerTalk] Drilling into a concrete slab

[K7LXC at aol.com]

In a message dated 3/6/03 1:16:16 PM Pacific Standard Time, 
kharker at cs.utexas.edu writes:

>     I am helping a university ham radio club with a tower installation
>  on an already-poured level concrete slab.  It will probably be a 40' Rohn 
>  45G tower bracketed once at about 20'.  We would like to put three or four 
>  bolts in the slab and drill holes in a Rohn 45G base plate to match.
>  
>       Can someone recommend a particular concrete anchor bolt and
>  cement/epoxy/whatever product?

    I prefer to use concrete epoxy to secure them. The last place I rented a 
roto-hammer had it. There is specific concrete epoxy. Actually just about any 
expoxy will work - the forces we're talking about are pretty small and the 
epoxy is generally much stronger than the concrete anyway.

    Expandable concrete anchors work too - just another way to do it. 
    
    You've got two choices for drilling a hole: 1) roto-hammer which is 
pretty fast and 2) concrete core drill. The core drill leaves a better hole 
but that's just a comment, not something that's too important. 
>  
>       What needs to be done to drill the holes properly?  What kind of 
>  drill and bit are needed, how do you keep the hole vertical, etc?
>  
    Use an oversize drill and let the bolt slop around a little. Then you can 
use the base plate to hold the bolts whilst the epoxy is drying. 

    The bolts can be a little off as long as they fit. There's no vertical or 
lateral stress on the bolts to speak of so since the plate is sitting on the 
concrete and all the stresses come out there with nothing on the bolts 
(except for a little tension while it's being climbed during assembly).

Cheers,
Steve     K7LXC