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Re: Light Pole Failure

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Dear Steve,

I'd place money on this one (but, not a stamp - that one is on you) :

First, I think that a 1/8" wall thickness is too light for the expected
service environment and height - suggest 3/16 or 1/4". As an alternate,
consider
1/4" for the lower 1/3, then 3/16" for the upper 2/3, but this requires
expensive welding, not worth the extra material costs.

Second, the pole needs to have at least four (4) tapered vertical stiffeners
(3/8") approx. 18 - 24" tall (fully welded) - an alternate would be to use
through plates (1 full + 2 halves). No need to cut, insert and weld the pole
into the base plate zone.

Thirdly, if first and second insights seem like overkill - then I'd look
long and hard at the use of such a large weld to such a relatively thin wall
shell.  All that heat could be changing some of the chemical composition,
maybe inducing some brittleness.

Last but not least is the 'shape' factor. I know that rectangular or square
shapes have a special visual appeal, but from an aerodynamic standpoint
during moderate to high wind conditions, I bet that pole is going through
some weird oscillations (fix base + FREE head) and possibly creating some
stress cracks at points of high and/or unbalanced shear zones. Maybe, round
sections should be considered a better choice.

Now the disclaimer - did not perform even one calculation - everything above
is based on pure, old-fashion ( and yes - that means age), gut feelings,
based on many years of experience and hard-knocks, and a dash of dare !  My
attorney wants me to reconsider this legal disclaimer, but it's going to
cost me - besides I think most understand it better than that attorney talk.

Have a great day Steve, and let me know what your hardwork and final
conclusions reveal !

John Hilzman, CEO
STEEL TECH INC.
----- Original Message -----
From: "Steve Hiner" <shiner(--nospam--at)folsom.ca.us>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, February 07, 2002 5:34 PM
Subject: Light Pole Failure


> Two light pole failures in the last three years ... doesn't sound like
many,
> but the failure mechanism is of some concern.
>
> Central California - 75 mph design wind speed
> Some strong winds occurred several months back (40-50 mph gusts)
> (Poles did not fail/drop during those storms)
>
> 30' tall poles with light standard (about 3 years old)
> 5" square steel tubes, 1/8" thickness (material spec - not sure)
> 12" +/- x 1" thick square base plate w/ 4 anchor bolts
> The base plates have 5" square holes such that the tube slides within the
> base plate thickness
> Fillet welds - all around (3/16" or 1/4"? +/-) at top of base plate to
tube
> AND at bottom edge of tube to 5" square slotted edge of base plate.
>
> Failure has occurred in the steel tube just above the fillet weld between
> the top of base plate and the tube section.
>
> Would be interested to hear some opinions or from those who may have
> experience with similar failures.
>
> You can also contact me personally at shiner(--nospam--at)folsom.ca.us
>
> Regards,
> Steven T. Hiner, SE
>
>
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