[TowerTalk] Anchor rods, 55 vs 105 ksi ??

[Jim Thomson]

The 'new'   spec for anchor rods is called ASTM- F1554.   They come in 36/55/105 ksi. 
The original spec for my HDX-689  used A36 anchor bolts [1.25"  x 36"  long x 36 ksi] 

The 689 never used  1.25"  anchor bolts   but 1.125' bolts.   I phoned US Tower, and they tell me the
correct rod for the 689 is now  28" long x 1.125" DIAM  X 55 KSI   [ASTM- F1554].    My local eng does not
like the miniscule  28"  long rods  [which have 6" thread on top].    The 6" threaded portion sticks above the
concrete by 6".... leaving only 22" embedded in the concrete.  A 1.125" rod only has a  3.5" circumference as is.

They also don't spec using any washer's /plates on the bottom of the anchor rods.  My eng wants the anchor rods
deeper into the concrete.. like  1/2 the depth of the concrete foundation.     Concrete foundation will be 
6' x 6'  x 9' deep.   He also wants the vertical rebars  changed from 7/8"  to 1".   He  wants the horizontal re-bars
changed from 1/2"  to 5/8".. and both 60 ksi.   He also wants  a grid of 5/8" rebars across the top,  so concrete
block is reinforced on 4 x sides + top.  He wants  5800 psi concrete to be used. [40 mpa]

OK,  I checked out these  ASTM F-1554 anchor rods.    60"  long... with 6" threads on BOTH ends of the rods. 
There is hardly any difference in price between a 55 ksi rod.. and a 105 ksi rod.... 13% !   

The 105 ksi rod is  105/55 =  91%  STRONGER.    13%  more $$  but 91%  stronger is almost like a free lunch. 

The heavy hex nuts are the same for both types of rod.  A194-2H  [175 ksi]  Hardened flat washers to be used on 
both sides of everything.... + split ring lock washers on top sides only... [ and ditto with below plates]

Local eng also wants  9"  square steel plates on the bottoms of the anchors.   The anchor rods on a 689 tower
are 3 x groups of 4 rods.   Each group of 4 x rods is in a square, with 5" C  to C spacing.   The 3 x  9" square plates
will increase the pull out capacity by a huge amount...esp with the anchor rods being embedded  54".. instead of the
22" factory spec... [no plates/washer's used on factory spec]  

I think Dino Darling, K6XD, wrote a section about anchor rods in the 2010 handbook.  Is there any reason not to use
the stronger  105 ksi anchor rods ??   The only thing holding the 5600 lb tower + ant's  to the 9' deep block of cement
is the 12 x anchor rods.  [ there is also 18 x 1" bolts, transverse mounted, that hold the 1/2" thick tabs of the tower legs
to the mating tabs of the 540 lb base plate] .  The 12 x Anchor rods hold the 540 lb base plate [1" thick steel plate, 50"
x 41"]  exactly 2"  above the concrete. The bottom's of the  12 x leveling nuts and washer's below the 540 lb plate
are exactly 3/4" above the concrete.   

This is the last place one wants to go cheap on a tower..esp when 13% more $$  buys you 91%  more yield strength,
and loads more tensile strength, shear strength, etc, etc.    My local eng thinks that 105 ksi rods may be too brittle, and
subject to fatigue, from wind loading. The only mech connection between sections on any crank up...is the raising cables
between sections, so I'd say it's a moot point.  IF the 105 ksi rods were too brittle, I don't see how they could end up
in the F-1554  anchor rod spec in the 1st place.    Any thoughts ?? 

Later........ Jim   VE7RF