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RE: Guard Rail

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The old BOCA and National Building Codes had provisions for vehicular impact.  After an incident in California in the early 1990's, the UBC picked up requirements for vehicular impact in parking garages for passenger cars. 
It was not predicated on testing, it was just predicated on what other codes had done. 
The theoretical vehicle is generally considered rigid, the arresting cables are not and will resolve the force into tension in the cables.  The problem is nonlinear and will not be the same as for rigid linear response. 
The AASHTO information is predicated on testing.  The Department of State also has information for resisting vehicular impact.  It is also predicated on testing. 

You can run all of the sophistocated computer analysis you want, and the testing will show that you are wrong. 

Harold Sprague

> Date: Sat, 26 Jul 2008 13:42:10 -0700
> From: MRKGP(--nospam--at)
> To: dmerrick(--nospam--at); seaint(--nospam--at)
> Subject: Guard Rail
> The new code requires a bollard to be designed for 6000lb, 18" above
> ground. The load is required to be increased to an unknown amount for
> trucks and buses.
> What testing is this based on? car weight? speed? Car model crushing
> energy absorption?
> I found where a tested medium sized truck at 120 mph is stopped with
> about a 17000 lb rigid capacity.
> So the code vehicle load must be for something traveling at least 60mph.
> Bollards, in a parking lot to prevent parking on a sidewalk, is an
> example where a lower speed impact might be more reasonable.
> I know that there is a liability to have rigid barriers along a highway
> due to the potential injuries to the vehicle occupants and so yielding
> barriers are part of highway designs. Looking at their post embeddments,
> the capacity is no where near to the 6000 lb as specified in the
> building code and using the code capacity for poles cantilevered into soil.
> Does one need to design for more than the legal speed limit?
> Does the impact reduce by the velocity squared?
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