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RE: Design of bollards

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I have been following this thread with interest.  One question that
comes to mind, which appears that nobody has asked, is whether or not
life safety is in question.  During the Gulf War I had the opportunity
to design temporary barriers to protect a nuclear ship building facility
from terrorists.  In order to construct as quickly as possible, we used
a series of industrial dumpsters filled with concrete.  These were
moveable with heavy equipment, but when stacked two and three deep will
eventually stop almost anything (even heavily loaded semis) in a very
short distance with little concern to whether the vehicle/driver would
survive.  

But I digress.  the question that comes to mind is whether or not you
want to design the impact so as not to kill the impactor.  I'm sure
building preservation is the reason behind the bollard requirement.  But
is it to protect from accidental or intentional collisions.  If
intentional, the stronger the better.  If it is accidental (such as
highway overpass columns), some sort of energy absorption system should
be considered.  As previously mentioned, planters tend to be a good
source for this purpose as the masonry walls will fail relatively easily
upon impact and the soil behind will absorb the energy rather than
transfer it back into the vehicle.


-----Original Message-----
From: Paul Crocker [mailto:PaulC(--nospam--at)ckcps.com]
Sent: Thursday, July 29, 1999 12:43 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Design of bollards



ASQUILALA(--nospam--at)aol.com wrote:

> I think some of our list members misundertood the above statement.  My
> understanding is that speed bumps are placed before the bollard to slow down
> the vehicle before hitting the bollards.  This is the proper way to make
sure
> that the vehicle will not hit the bollard at top speed.
> Placing only speed bumps instead of bollards will definitely won't gonna
> work.

As I understand several of the post, people are questioning whether
using speed
bumps to limit the speed at which a vehicle can hit a bollard is
effective, since
vehicles can cross speed bumps at very high speeds if damage to the
vehicle is
not an issue.  A speed bump may be sufficient to limit the speed if your
concern
about the bollard capacity is mainly for minor accidents and superficial
damage
to a building exterior (such as a fast food drive through), but a speed
bump
probably does not help reduce the speed of impact if you are concerned
about
deliberate acts of violence or high speeds accidents in general.  If
life safety
is the issue, it might be advisable to design the bollard for a high
speed
impact, regardless of the presence of speed bumps.  If the bollard
cannot
tolerate such impacts, there are many option, such as jersey barriers,
large
planters, etc.  The massive concrete flower planters springing up around
government buildings around the country aren't just for looks, after
all.
Forcing a vehicle to make a right angle turn immediately before
approaching
whatever your don't want to get hit is also effective (assuming the
approach is
sufficiently limited that a vehicle can't just come straight at the
location some
other way, like across a lawn), since the speed that a vehicle can
negotiate a
sharp turn is limited.  That approach has been used in front gate
designs since
Biblical times (since sharp turns also slow down unruly mobs and
charging armies)
and is evident in fast food drive throughs.  Even in small spaces,
speeds can get
very high, so it pays to be careful.  A vehicle in a parking garage near
my
office went out of control last year (driver had a heart attack) and hit
a
concrete column at an estimated 70 mph.  I wouldn't have guessed that
you could
get up to 70 mph in a parking garage straight-away.  It was a big car,
too, and
managed to put some large cracks in the column.