Metal fence posts: Critique

[HeyBub]

My home backs up against a 200'-wide high-voltage power line easement. After Ike, looking across this field, I can see maybe thirty fences knocked down by the high winds. Every one of these downed fences was erected using wooden posts.

On my side of the field - for reasons passing understanding - every one of the fences remained intact and every one of the fences was erected using metal poles.

In the interests of full disclosure, we did have one break on our fence; the wind, using the pickets as a sail, fractured one cross-member, but the poles on either side of the fracture remained upright.

Maybe the construction technique using the wooden posts was flawed, I can't say for sure. But the metal post method survived the storm and the wooden posts didn't.

[willshak]

on 10/3/2008 8:49 AM HeyBub said the following:

What type of fencing material was between the metal posts? High winds are less likely to knock down chain link, wrought iron, or aluminum fencing than wood picket or board fencing, only because the winds can pass through the thinner metal fencing easier than the wider wood fencing..

[dpb]

...

...

That would be one of my first questions, too, as well as relative ages and more thorough investigation of the construction.

But, I'd guess a great deal of it was simply relative surface areas as just the WAG...

[Blattus Slafaly]

Metal fence posts are usually anchored in concrete and wood are usually just driven into the dirt.

[Tony Hwang]

Hi, Identical picket material between two fences? If not, your conclusion is flawed. Near the HV power lines? Not a good location to live.

[HeyBub]

Good question and I apologize for the omission.

In all the cases, the fences were cedar or PT pickets, 6' tall with negligible gaps between the pickets.

[HeyBub]

Virtually identical material (cedar of PT pickets). As to location, it has it's advantages.

1. No neighbor behind me to throw garbage over the fence.
2. Conversely, I can throw garbage over the fence and no one complains.
3. My cats can prowl to their hearts content - very little hazards like cars.
4. It's kinda cute to watch glowing bunnies, at night, hopping around, taking care of their bunny-business (odd, though, my cats don't glow as much as the rabbits).

[dpb]

...

Still to many potential variables to answer specifically. One would guess as another wrote that the metal posts were set in concrete while the wood weren't and/or were deeper. Another question would be was the failure mode turnover of the post or did they break off? Age and amount of rain/water would also be effect as would, potentially, the wind direction and effective shielding perhaps of one side of the cleared area vs the other such that despite proximity actual wind loadings weren't the same...far too many possibilities yet to draw definitive conclusions.

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[Tom G]

Poses the question; Why do tornados demolish all of the houses on a block and leave one untouched? Perhaps the houses on your side of the transmission line blocked the wind enough to save your fences, perhaps those fences blocked the wind to save your fence but suffered as a consequence. Several times the winds have torn up the trees on the vacant lot next to me and left my trees alone. Mother Nature does as she likes, I guess.

Tom G.

[TD]

"HeyBub" wrote in news:6aadnWuRodVxiXvVnZ2dnUVZ [e-mail]:

Our fence was installed in the 1970s with galvanized posts. The fence still stands (tho kinda ugly).

[Robert Blass]

On 03 Oct 2008 20:05:17 GMT, TD sayd the following:

is it electric fence?

volts?

Mine needs to be 80-100 voltage AC range with 50K pulses in first 1ms

[HeyBub]

I agree. Wind direction, streaming neutrinos from the Solar Wind, Voodoo, or a malevolent foreign deity may be behind the difference. Still, some thirty of my neighbors' fences built with wooden posts are all in a pile while a similar number using metal are still standing.

[SteveBell]

My first thought when I saw your post was that one side of the right-of-way was upwind and the other was downwind. The upwind side would be in the wind shadow of houses and trees. On the downwind side the wind would be able to get a little meaner as it passed under the power line towers.

[HeyBub]

Also a good point. However, being in Houston, the wind went one way, then, when the eye passed, the wind with the other. It averaged out.

In the aftermath, I saw a LOT of wood things down (mostly trees), but very few metal things (like light poles, fireplugs, or street signs) blown down. Empirical evidence supports the theory that wood sucks.

[misterjustme]

Steel is stronger then wood and does not weaken over time like wood.

[dpb]

HeyBub wrote: ...

You've still not even established the failure mode...

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[HeyBub]

Oh.

Sorry.

Failure mode: Fences fell down due to wind (99.998% confidence factor).

[dpb]

No, that's cause, not mode...did the posts come out of the ground or did they break?

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[HeyBub]

Oh.

I didn't know, so I went and looked.

They broke. At ground level. Many "stumps" remained, stuck in concrete.

Evidently they rotted at ground level or below and just died of shame.