Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Failures

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I noticed a few previous posts referred to various bldg failures of some sort
or another -- the posts of Kate O'Brien, Tim McCormick, and Drew Norman come
to mind.

I'd appreciate first hand accounts of failures that various engineers have
witnessed.   Drew's example of improperly braced trusses was particularly
instructive.  Perhaps those with a lot of experience can share it with regard
to this topic.  For example, I imagine City inspectors would be more likely to
have seen failures and have a greater catalog to report.

These might also spark some code debate.

I'll start, for what it's worth:
I did a repair job to a golf driving range in San Francisco.  It's visible
from 280.  The existing class H1 wood utility poles had been designed to an
ANSI standard for wood telephone poles to a height of approx. 70 feet.  They
support 1" mesh netting.  The owner had extended the poles with sched. 40 pipe
another 20 feet.  During those great big winds of winter, 1995/96, one whole
row snapped like matchsticks about ten feet up from the ground.
Luckily no one was hurt, but nearby power lines and cars were damaged.  I had
been telling my clients that they should have snapped near the ground -- I was
surprised that they broke at ten feet up, since I'd assume maximum moment was
at the base.  (It could be due to the taper of the poles.)  And they all broke
at this height, ruling out the odd check, void, or flaw.
On the opposite side of the range, the poles were more sheltered from the
wind, and no poles broke.  You can imagine that the owner chose to replace
only the side that had broken.
I suppose failure was due to two main causes: winds in excess of design
windspeed, and extension of the poles without regard to engineering.  Due to
the increased lever arm, this addition doubled the moment demand on the pole.
In addition, wood has a brittle failure mode here, and is not a good choice
for this application.  The steel replacements have a reinforced concrete core
up thirty feet -- I convinced the owner to design for a higher windspeed based
on risk/return and cost/benefit considerations.  But I still couldn't talk him
into doing the other side....

Any more out there?  Thanks,
Brian Veit, P.E.