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RE: Light Pole Failure

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Steve,

A scanning electron microscope in the hands of a good forensic metallurgist
can determine if the failure was due to cyclic fatigue or not.  The trick is
to have fairly pristine sample.

If the failure is fatigue at the HAZ, adding stiffeners might just be moving
a future failure point higher on the light pole.  Eventually you will have
stiffened the entire length of the light pole.

One challenge is the heat input required for the 1" base plate is
significant.  The amount of heat could cause serious undercuts in the 1/8"
thick light pole.  There are welding methods on thin sections that aren't as
prone to creating "hard spots" on thin sections.  You might try preheating
the plate or TIG welding.

Regards,
Harold O. Sprague

> ----- 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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