HI DENNY...SEE CAPS.
----- Original Message -----
From: "Dennis OConnor" <ad4hk2004@yahoo.com>
To: <towertalk@contesting.com>
Sent: Monday, January 16, 2006 7:19 AM
Subject: [TowerTalk] Screw Anchor Question
> I have two towers, 130' lightly loaded and 150' with LARGE antenna loads -
way, way beyond Rohns data for 25G... They are installed with screw
anchors into sandy ground... They have been up more than ten years without
any incident or evidence of failure... Storms with recorded gusts to 89 mph
have happened over those years... In Michigan we have freeze thaw cycles up
the bungees...
>
> So why does it work for this clueless ham?
LUCKY? LOTS OF BUILT-IN REDUNDANCY (GOOD IDEA!)? NON-CORROSIVE SOIL?
> Well, ol clueless here designed and installed it so that there is a
separate anchor for every 60 feet of tower, i.e. only two guys per anchor...
And the steepest guy angle to any anchor is 45 degrees, while it's lower
mate is roughly 30 degrees... My suspicion is that the tower sections will
bow enough to gyrate and twist the tower down before the guy anchors will
pull out... Limiting the load to each screw by keeping the guy wire angle
low, is the key in my book...
I DON'T MEAN TO COME ACROSS AS ANTI-SCREW ANCHORS, I'M NOT, I'VE JUST BEEN
SAYING ONE OF MINE FAILED AFTER ABOUT 15 YEARS, RESULTING IN TOTAL
DESTRUCTION OF THE TOWER & ANTENNAS. I WAS SAD.
THE ANCHOR CAPABILITIES OF THE SOIL NEVER FAILED ME, IT WAS THE SLOW
GALVANIC ACTION ON ONE OF THE ANCHORS THAT DID. IN MY CASE I HAD A 70' TOWER
WHICH HAD A RATHER LARGE TRIBANDER ON IT PLUS A 20' DECIBEL PRODUCTS UHF
ANTENNA (ONE OF THOSE FOLDED DIPOLE JOBS); I WOULD CONSIDER THE TOWER
LIGHTLY OR MODERATELY LOADED, CERTAINLY NOT OVERLOADED. WE OCCASIONALLY GET
70 MPH WINDS, WHICH IS ALL THE TOWER IS SPEC'D FOR, AND IT HAD SURVIVED
NICELY. IT WAS ONLY A 50 MPH WIND WHICH BROUGHT IT DOWN, BUT THE WIND SPEED,
DIRECTION, AND CONDITION OF THE ANCHOR ROD WERE ALL "RIGHT" FOR THE FAILURE.
I LIKE YOUR DESIGN OF SPREADING THE LOAD OUT, AND IT SOUNDS LIKE YOUR SOIL
COMPACTION IS RIGHT FOR THE LOADS. YOU DO SCARE ME WITH HOW YOU DESCRIBE THE
LOADING OF THE 150 FOOTER, BUT I HEAR YOU GUYS UP IN MICH HAVE BIG STONES,
SO IF YOU CAN SLEEP AT NIGHT...COOL!
73
dAN
K0DAN
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|