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Re: Stopping That Truck !!

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Stan,

This may be of no help whatsover, but .....

"Crash tested' traffic railings are used by many, if not most or all, state
DOTs.  If I remember correctly, some of the testing was done in Texas,
probably at one of the universities.

You may want to check with the TxDot bridge engineers (is the head office
still in Austin?) to see if they have any information that may be useful.
I'm not thinking that they can give you an exact answer, just some idea of
how the truck and cables, bollards, etc. may interact.

Vaguely,
M. David Finley, P.E.
Lake City, FL  32025

----- Original Message -----
From: "Caldwell, Stan" <scaldwell(--nospam--at)halff.com>
To: "'SEAINT Listserv'" <seaint(--nospam--at)seaint.org>
Sent: Wednesday, January 23, 2002 10:32 AM
Subject: Stopping That Truck !!


> Greetings, y'all:
>
> Every now and then, and interesting problem comes along that is
challenging
> in its simplicity.  It is even more interesting if that problem is
entirely
> outside the realm of all common building and bridge codes and guidelines.
> Structural engineers simply are ill-prepared to tackle problems which
> involve moving objects, momentum, kinetic energy, potential energy, force
> due to deceleration, and acceptable structural failure.  We are struggling
> with just such a problem right now:
>
> A client in the defense industry wants to construct a security fence
around
> the perimeter of their industrial campus.  The fence is to be comprised of
> bollards nominally spaced at 12 ft., connected with a continuous wire
rope.
> Each bollard will be comprised of a 12" X 12" concrete post over a 18"
dia.
> concrete pier.  The posts will extend about 3 ft. above grade, and the
piers
> will extend 6 ft. to 8 ft. into black clay.  Reinforcement will be
> continuous between the piers and posts, either with #8 rebars or with
small
> rolled shapes.  The 1" dia. wire rope will pass through the bollards about
> 30" above grade, and will sag about 2" between bollards.  The client has
> specified that the fence must stop a 7500 lb. truck with a C.G. at 3 ft.
> above grade, traveling at a speed of 20 mph or less.
>
> Question:  What is the design force on the bollard?  on the wire rope?
>
> Six normally intelligent structural engineers have calculated answers
> ranging form 3 Kips to 980 Kips, with the majority thinking somewhere
> between 50 and 100 Kips.  What do you think?
>
> Before you jump to an answer, you should consider the following factors:
>
> 1]    The softest, and least known, spring is the soil ... and it's
> stiffness changes seasonally.
>
> 2]    The next softest, and ill-defined, spring is the truck bumper and
> chassis.
>
> 3]    The bollard can "fail" into a full plastic hinge (or beyond), just
as
> long as it stops the truck.
>
> 4]    The two most important variables are time and distance, which, of
> course, are both indeterminant.
>
> Who out there can think "outside the box" and solve this problem?
>
> Stan R. Caldwell, P.E.
> Dallas, Texas
>
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