Topic: Annemometer Tower Blown Over.

[ocala]

While going through the damage reports from todays squall line that went through Florida I came across this. I just find it hard to believe that a tower supported with guy wires would go down in winds that low.

1032 AM     TSTM WND GST     LAKELAND HIGHLANDS      27.96N 81.95W
04/15/2007  M55.00 MPH       POLK               FL   TRAINED SPOTTER

            MEASURED AT 30 FEET ABOVE GROUND LEVEL. RECORDED GUST OF
            55 MPH BEFORE EQUIPMENT COLLAPSED. PERSON HAD ENHANCED
            STEEL STRUCTURE WITH GUY WIRES PRIOR TO THE EVENT. WIND
            MAY HAVE BEEN 60 MPH TO CAUSE EQUIPMENT TO BREAK. NO
            FURTHER DAMAGE REPORTED.

[SLOweather]

Yeah, that sounds a little weird. We've measured 50-55 MPH winds on a Davis anemometer, mounted on an unguyed steel mast pipe with no damage.

[Mark / Ohio]

I would guess it was nearly rusted off at the base.

[kray1000]

That is hard to believe, considering all the tropical systems and squall lines that blow through Florida.  Would be interesting to know how long the tower was in place...

[capeweather]

That does seem kind of weak. When hurricane Wilma came through here we recorded several 69mph wind gusts and I was using a PVC pipe about 4' long on my roof. I no longer have that setup but was surprised it held. Now for a tower to fall from this storm almost seems like somebody forgot to tighten some bolts down.  

[edpnjax]

That does seem kind of weak. When hurricane Wilma came through here we recorded several 69mph wind gusts and I was using a PVC pipe about 4' long on my roof. I no longer have that setup but was surprised it held. Now for a tower to fall from this storm almost seems like somebody forgot to tighten some bolts down.

Mine used to be on PVC as well, but it held all through the 2004 hurricanes.. it's now mounted on top of the boat house on a mounting mast from an old DirecTV dish. That mounting mast is the perfect size and height.

[Scalphunter]

How much corrosion was on the inside or on the legs. All it  takes is a sligth buckle  of one support  and it will come down.

[GvlSkywarnNCS]

Overtightening the guy wires or placing them at the wrong level can also bring a tower/mast down, but being in FL I'd bet corrosion was the cause here. Some months back a Ham died when the tower he was disassembling fell, probably because they guys were maxxed out so when one snapped the others pulled it too hard and it collapsed under him. I had a 42in J-pole antenna made of 1/2 in copper pipe atop 3 ft of 1 1/4 Sched 40 PVC on my mast when I recorded a 70MPH gust 10 feet below the bottom of the antenna. And to top that off, the antenna/PVC pipe connection was a 3/4 in screw-thread PVC reducer fitting which I figured was a weak point. That's a lot of leverage on the pipe and fitting but it held! PVC deteriorates with UV exposure so if it's 5 years old and you've got to take it down for other work, go ahead and put new pipe up in it's place- it's cheap insurance.

The only PVC mast I ever lost was 20 ft of 1 in Sched 40(2 sticks) and guyed only at the top. It didn't fall but the compression load from the guys turned it into a series of curves which got worse quickly after I retightened the guys so I had to junk it all. Next time I'll stay about 1/5 down with the top guys, leave them on the verge of loose and add another set of guys maybe halfway up and slightly tighter. The PVC will flex quite a bit before breaking and that should take this into account without adding compression.

The best 'bang for the buck' is chain link fencing's "Top Rail" pipe. About 1 1/4 inch, galvanized, and can be had in up to 16' sections. Not as good as the TV antenna pipe but OK for lightweight or low wind load use (such as a WX station) it'll hold in at least 100 MPH winds which will usually have already taken out most mounts or whatever they (used to be) tied into  With a freestanding "top rail" mast I'd guess you could go 12-13 feet without a problem- more than that and I'd guy it appropriately.

[Mark / Ohio]

I had a customer once ask me after installing a Directv dish if I would take down their 50'-60' three leg tower for them.  It was solid rust  including what guys were still attached, standing in a pasture on a pretty steep hillside.  It was already leaning sort of toward the house and probably had been there by the looks of it 40 years with no maintenance.  I declined.  Told them their best bet would probably be to take one of the farm tractors and give a nudge toward the clearing and once it started to go throw the tractor in reverse and get back away as fast as they could and whatever they done not to try to climb it.   

I knew a guy that was on one like that when it went down.  Of course once it starts to go your legs can't move fast enough to get to the ground.  Fortunately for him he made it nearly halfway down as it went over.  It landed across an alley on a neighbor's garage roof and came to a stop with the guy hanging by his belt about 8' above the cement in the alley where he could unhook his belt and drop to the ground.  Talk about a bad day turning into a lucky one!  Last I heard he's never taken a job on one taller than 3 sections (30') after that.