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RE: Design of bollards[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Design of bollards
- From: "Jeffery Seegert (x 485)" <jbseegert(--nospam--at)matrixti.com>
- Date: Thu, 29 Jul 1999 14:15:26 -0400
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.
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