Bollard Design 1

[msquared48]

Ran into this thread linking to a good article from "Structure" magazine from 10/08.

Need to confirm bollard design for vehicle impact

thread507-244205

My question, though, is, in the circumstance where there is a 6" precast vehicular curb before the bollard/guardrail, has anyone run across any allowance for decreased impact momentum in the design of the bollard below what is recommended on page 6 of the article in the graph?

Seems like some energy would either be absorbed, or translated into vertical motion. Quantifying that is the problem. Additionally, I am concerned about is the normally very nominal degree of attachment of the precaast curb to the parking area - a couple of pieces of 1/2" rebar 2' long into the paving and soil substructure. I have seen a lot of these precast units failed in shear/lateral soil bearing at the top of the A/C paving giving me little hope of generating much energy absorbtion relatred to the recommended design forces seen in the article.

My instinct tells me to ignore the curb.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Teguci]

No energy loss assumed due to curb. Usually detailed a 30" long, 3/4" dia coil rod cast into the wash between the precast spandrel and precast double tee. Never made me feel warm and fuzzy, but is industry norm.

 

[msquared48]

Thanks. You confirned my suspicions.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ACtrafficengr]

How far apart are the bollard and the curb? What is the speed and angle of impact? Above ~40 mph, the vehicle may vault over an obstacle between 1 and 10 feet from the curb.

A bit beyond 10 feet, the vehilcle is likely to hit lower than expected, as the vehicle comes down and the suspension compresses.

There was a multiple fatality accident in NYC a month or so ago where a vehicle hit a curbed "safety walk" on a bridge, and went over the side of the bridge. The guiderail was completely untouched.