[TowerTalk] Rohn 25G Hardware

[Roger D Johnson]

  After posting my previous message, I decided to do some research
to determine the strength of the SS hardware I used on my tower.

  It turned out to be more complicated than I thought. I soon got
bogged down with SAE vs ASTM standards, old bolt head markings vs
new head markings, psi vs ksi vs kips, etc. I'll try to briefly
summarize my findings.

1. There is not much data on the shear strength of bolts. One site
gave the following figures. For carbon steel, the shear strength is
approx 60% of the tensile strength. For SS bolts it's 55%.

2. Some of my bolts are marked with two lines at 90 degrees. These
are an example of the "old marking" and are 18.8 stainless (also
known as 304SS). These bolts seem to vary widely in strength.

3. I also have bolts marked F593C. These are cold worked and conform
to ASTM standard F593. These bolts have a tensile strength of 100 to
150 ksi (ksi = 1000 psi) giving them a shear strength of 55 to 82.5
ksi. This compares favorably with grade 5 carbon steel bolts which
are rated at 120 ksi tensile strength.

For more info on the F593 bolts see:

http://www.marfas.com/technical.shtml

  Based on the two anecdotes I've read here, it doesn't seem to make any
difference what bolts are used when the guy system fails! My conclusion
is that F593 SS hardware is fine for guyed towers. Self supporting 
towers are a different story.

73, Roger