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RE: Light Pole Failure

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John,

Thank you for the thoughtful response.

One question ... would the 4 vertical stiffeners referred to below be welded
at the center of each 5" face of the pole.  If so, do you see any problems
with the bending that would be placed on the tube thickness?  Or is that why
the stiffeners are recommended to the 18 - 24" height?  Gut feeling of
course.

Regards,
Steve




-----Original Message-----
From: Steel Tech N.A. Inc. [mailto:jhilzman(--nospam--at)steel-tech-na.com]
Sent: Thursday, February 07, 2002 7:53 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Light Pole Failure


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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