[TowerTalk] Anchor Bolt Grade Suitable for Tower Base?

[Jim Lux]

At 09:18 PM 9/13/2005, Richard (Rick) Karlquist (N6RK) wrote:
> > I am installing an LM-470 and prefer to use a base plate for the tilt
> > base that was designed for retrofit to an already existing concrete pad
> > and anchor bolts.  The base plate takes three 1-1/2" anchor bolts, which
> > will be 27-36" long.  I have purchased 10 feet of 1-1/2" threaded rod
> > that meets ASTM specification A307A,B or C.  Apparently, the stuff is
> > known as "common" threaded rod and is the lowest strength available.  Is
> > this rod suitable for this application?
> >
> > Tnx and 73,
> >
> > Joe
> > K2XX
>
>It seems to me that the strength of the concrete limits the safe load
>you can put on anchor bolts to a low enough value that ordinary steel
>is good enough for the bolts.


I was chatting with a structural guy a few months ago about things like 
chemical anchors for patio covers and the like (a low load 
application).  Turns out that "taint necessarily so".  The problem isn't so 
much the strength of even crummy grades of steel, even aluminum rod would 
be strong enough from a materials point of view. The problem but the 
uncertain quality of manufacturing in the threaded rod or bolts.  Things 
like voids, cracks, or inclusions can raise problems because they cause 
stress concentrations.  When Home Depot goes to the "lowest backyard forge 
bidder" in a third world country (or more properly, some consolidator who 
contracts with dozens of these little manufacturing plants) you run the 
risk that they just dump any old steel from the ship breaker in India into 
the melt, then rolled out the rods, rolled the threads, dumped it into the 
plating bath, and loaded it into the container.  Unless the rod actually 
fell apart coming out of the machine, it's unlikely it was ever really 
checked.  They literally cannot afford to do any process controls or 
inspections.

You could either buy cheap stuff and inspect the heck out of it (something 
most hams don't have the equipment or patience for) or spend twice as much 
and get something that comes with the process controls and source 
inspection. (not saying that there's not bogus junk out there, and outright 
fraud, but it's less likely)