Parking Lot Entrance Gate Bollard Foundation 2

oengineer · Jan 12, 2018

Does anyone have an expression, or a procedure, document, or a spreadsheet for determining the depth and diameter for entrance gate pole foundation? I am treating the foundation like a bollard.

Any suggestions/comments are appreciated.

JAE · Jan 12, 2018

Bollards are either psychological barriers (won't actually resist an impact but scare people away from trying)....

or....

They are fully functional impact resistant bollard systems designed (well not really) to resist a particular mass traveling at a particular speed.

The first is whatever you want to do relative to foundations - a small diameter concrete pier x 4 ft. deep with the pipe bollard set into it.
The second is a fabricated and field tested product. There aren't many calculation procedures, if any, to get you a "design".

For an entrance gate - with a pier taking lateral loads, there's this old nomograph (see also pdf attached):

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azcats · Jan 12, 2018

I see so many gates that sag due to foundation movement. I've never investigated enough to see if they are just shallow piers that have been under designed or not designed at all. You wouldn't need to convince me very much to put an extra foot or two on my design. Or neglect the top foot or two of earth.

Anyway - the chapter 18 IBC equations are my go to for pole embedment. (1807.3.2.1 in 2012 IBC) It is iterative.

This online calculator appears to match my spreadsheet. Although it does not limit 'd' to 12' as described in that code section.

https://www.engineersedge.com/calculators/flagpole-base-design-calculator.htm

SlideRuleEra · Jan 12, 2018

Agree with JAE about two "uses" of bollards. I had the opportunity to design a few for our electric generating stations, then see how they performed over the next several years. Our goal was to have sacrificial, impact resistant bollards. That is, the pipe survives (more or less unbent) but the bollard is "uprooted" when hit. The idea being to minimize damage to the impacting vehicle, but also stop it in a short distance - before striking important equipment or groundwater monitoring wells.

For low-speed (say 25 MPH, or less) autos, pickups, small forklifts, etc. we found that nominal 4" diameter, schedule 40 steel pipe, filled with concrete was a good compromise. For low-speed off-road trucks, bulldozers, large front end loaders, etc., 6" diameter was better.

Details of embeddment depend on the soil. We typically had poor soil, so would embed the 4" pipe about 4', the 6" pipe about 5'. The pipe was encased in a concrete cylinder with a diameter 3 times the pipe diameter (12" diameter for 4" pipe... 18" diameter for 6" pipe). For a few feet in all directions, the bollard is surrounded only by soil - to make sure the bollard "uproots" cleanly.

The 6" diameter bollards worked well... when hit by the intended heavy equipment. The 4" bollards, perhaps a little too "strong". I would cut down 4" pipe embedment a little.

http://www.SlideRuleEra.net